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GCE-LTER Journal Articles

Alber, M. 2002. A Conceptual Model of Estuarine Freshwater Inflow Management. Estuaries. 25(6B):1246-1261.

Abstract
As humans continue to influence the quantity, timing, and quality of freshwater input to estuaries, an increasing number of places are working to set minimum inflow requirements for their systems. This paper puts forth a conceptual model that explores the roles that science, management, and society play when it comes to setting inflow policy. The premise is straightforward: freshwater inflow affects estuarine conditions, which in turn impacts estuarine resources. The scientist works to quantify the relationships among these components and to understand their causative mechanisms, and policies in different estuaries have been set based on the response of one or another of these components to changes in inflow. However, it is important to recognize the influence of both society and management on this process. Whereas an estuarine scientist might identify an indicator species as an estuarine resource and work to establish the link between salinity and its distribution, 1) this specific species will not necessarily have broad general appeal as a resource to society, and 2) a manager cannot directly change its distribution. Society generally acts to protect those estuarine resources and functions that have been identified as "valued" by a broad coalition of stakeholders. The management options available to protect these resources, however, are almost invariably restricted to factors that directly affect inflow (e.g. evaluating withdrawal applications, establishing release schedules for dams) because this is where humans have control over the process. This conceptual model is used to provide an overview of the impacts of decreases in freshwater inflow to estuaries, and to explore the inflow-based, condition-based, and resource-based approaches that have been taken in several systems to establish estuarine inflow requirements.

Alber, M. and O'Connell, J. 2019. Elevation drives gradients in surface soil temperature within salt marshes. Geophysical Research Letters. 46:5313-5322. (DOI: https://doi.org/10.1029/2019GL082374)

Abstract
Elevation differences in salt marshes result in numerous ecological consequences as a result of variation in tidal flooding. We demonstrate here that elevation differences are also negatively correlated with soil temperature on the marsh platform, irrespective of tidal flooding. Field observations of soil temperature at 10‐cm depth in a Georgia marsh showed that elevation increases of 0.5 m corresponded to decreases in average soil temperature of 0.9–1.7°C during both winter and summer. Landsat 8 estimates of land surface temperatures across the marsh in dry (nonflooded) scenes also showed that temperature decreased with increasing elevation, which was consistent with soil observations. Similar satellite results were also found in a test marsh in Virginia. Biological reactions are temperature‐dependent, and these findings indicate that metabolic processes will vary over short distances. This is important for accurately estimating marsh metabolism and predicting how changes in temperature will affect future productivity.

Alber, M., Reed, D. and McGlathery, K. 2013. Coastal Long Term Ecological Research: Introduction to the Special Issue. Special Issue: Coastal Long Term Ecological Research. Oceanography. 26(3):14 - 17.

Abstract
The US National Science Foundation's Long Term Ecological Research (LTER) network was established in 1980 to provide the scientific expertise, research platforms, and long-term data sets necessary to document and analyze environmental change (http://www.lternet.edu). There are currently 25 sites in the US LTER network representing a range of ecosystems, including deserts, prairies, forests, tundra, lakes, urban areas, estuaries, coastal reefs, the pelagic ocean, and production agriculture. Although the research questions being addressed vary across the network, each site collects data on primary production, population dynamics, the cycling of both organic and inorganic matter, and disturbance patterns. Long-term data in these core areas enable changes in critical ecological processes to be tracked over time and facilitate comparisons among different ecosystem types.

Alber, M., Swenson, E.M., Adamowicz, S.C. and Mendelssohn, I.A. 2008. Salt marsh dieback: An overview of recent events in the US. Estuarine, Coastal and Shelf Science. 80:1-11. (DOI: 10.1016/j.ecss.2008.08.009)

Abstract
This paper provides an overview of the marsh dieback events that have been observed along the east and gulf coasts of the U.S. over the past decade. It is likely that some of the recently reported changes in marsh vegetation were affected by physical or biotic disturbances that are known to generate bare areas, such as overgrazing or wrack smothering. Other areas may be experiencing a state change such as that caused by long-term changes in sea level. However, sites in many areas are not readily explained by these causes and are considered to have experienced “sudden dieback.” In such cases, there are observations that the above-ground plant material thinned or browned or, in some cases, failed to re-emerge in the spring; the dieback occurred over a period of months and usually affected multiple sites within the area; and there is evidence that these events are transient (through successful transplants or natural regrowth/recovery), although some areas take years to recover. We explored the potential linkage of dieback with drought (as characterized by the Palmer Severity Drought Index), and found that there is evidence for an association in the southeast (GA and SC) and the Gulf (LA), but not in the mid-Atlantic (DE, VA) or northeast (ME, RI, CT). We also review the evidence for potential causes of sudden dieback, including changes in soil chemistry, fungal pathogens, top–down consumer controls, and multiple stressors. There is currently no single explanation that can be applied to recent dieback. We highlight the need for the development of improved diagnostics that will allow us to better classify dieback areas and provide evidence for (or against) potential causes.

Alberti, J., Casariego, A.M., Daleo, P., Fanjul, E., Silliman, B.R., Bertness, M.D. and Iribarne, O. 2010. Abiotic stress mediates top-down and bottom-up control in a Southwestern Atlantic salt marsh. Oecologia. 163:181-191. (DOI: 10.1007/s00442-009-1504-9)

Abstract
Increasing evidence has shown that nutrients and consumers interact to control primary productivity in natural systems, but how abiotic stress affects this interaction is unclear. Moreover, while herbivores can strongly impact zonation patterns in a variety of systems, there are few examples of this in salt marshes. We evaluated the effect of nutrients and herbivores on the productivity and distribution of the cordgrass Spartina densiflora along an intertidal stress gradient, in a Southwestern Atlantic salt marsh. We characterized abiotic stresses (salinity, ammonium concentration, and anoxia) and manipulated nutrients and the presence of the herbivorous crab Neohelice (Chasmagnathus) granulata, at different tidal heights with a factorial experiment. Abiotic stress increased at both ends of the tidal gradient. Salinity and anoxia were highest at the upper and lower edge of the intertidal, respectively. Nutrients and herbivory interacted to control cordgrass biomass, but their relative importance varied with environmental context. Herbivory increased at lower tidal heights to the point that cordgrass transplants onto bare mud substrate were entirely consumed unless crabs were excluded, while nutrients were most important where abiotic stress was reduced. Our results show how the impact of herbivores and nutrients on plant productivity can be dependent on environmental conditions and that the lower intertidal limits of marsh plants can be controlled by herbivory.

Alberts, J.J., Takacs, M. and Schalles, J.F. 2004. Ultraviolet-Visible and Fluorescence Spectral Evidence of Natural Organic Matter (NOM) Changes along an Estuarine Salinity Gradient. Estuaries. 27(2):296-310. (DOI: 10.1007/BF02803386)

Abstract
A transect of the St Marys River estuary fronl above the point of maximum salt wedge penetration to coastal salinities was conducted in July 1999. None of the parameters examined - dissolved organic carbon (DOC) content, UV light absorbance at 254 nm and Total Luminescence spectra follow the rule of conservative mixing. The characteristics of the different molecular size fractions of the St Marys River natural organic matter (NOM), as well as the results of a laboratory mixing experiment, provided evidence that loss of larger molecular size compounds from riverine NOM may occur by coagulation at salinities up to 10. An apparent gain of carbon in the lower estuary was attributed to exports from abundant coastal marshes in this area. The Total Luminescence spectra of the riverine NOM can be described by two peaks, centered respectively around 340/445 nm, and 230/430 nm Excitation/Emission Wavelength Pair (EEWP), which are characteristic of humic materials of aquatic origin. The samples from the high salinity stations exhibit peaks at lower emission wavelength EEWP 320/424 nm which can be considered as marine humic-like material. The presence of amino acid-tryptophan like peaks were observed, with EEWP 300/350 nm in some of the high salinity samples. This peak was of high relative fluorescence intensity. It is hypothesized that the intense biological activity of the salt marsh and near coastal area is responsible for the carbon addition as well as the appearance of the highly fluorescence amino acid-protein like material.

Alexander, C.R. Jr., Hodgson, J. and Brandes, J. 2017. Sedimentary processes and products in a mesotidal salt marsh environment: insights from Groves Creek, Georgia. Geo-Marine Letters. 37:345-359. (DOI: 10.1007/s00367-017-0499-1)

Abstract
Southeastern salt marshes are important repositories of sediment and carbon, and their formation is heavily dependent on deposition and accumulation of inorganic sediment. This study examined Groves Creek marsh near Savannah, GA, a typical Spartina alterniflora salt marsh of the southeastern US. Analyses were focused on the character, deposition and accumulation of material within the marsh on daily, monthly, decadal and centennial timescales, to determine the dominant factors in material supply and redistribution, and on its stratigraphy to determine the 1,000-year history of Groves Creek salt marsh development. Modern processes create gradients in grain size, which shows little variation from the tidal channel flanks up to mean sea level, and which coarsens with distance into the marsh from mean sea level to mean high water. This unexpected result suggests that,although floc transport is an important mechanism of sediment supply near the channel margins, energetic events must supply coarser materials to the marsh platform, where they are notreadily removed by typical energy regimes. Daily deposition can approach ~3 g/cm2 year; however, centennial accumulation rates are orders of magnitude lower (0.11±0.05 g/cm2 year) and are similar to those present over the past 300 years (0.05–0.2 g/cm2 year), indicating that much of the daily deposition is remobilized. Stable isotopic δ13C (average –18.7‰) and δ15N (average 5.7‰) values most likely indicate a large contribution from S. alterniflora as a carbon source throughout the marsh, although heavier δ15N on the channel flanks suggest that benthic algae may be locally important. Geologic, geochemical and microfossil evidence suggests that depositional conditions in the Groves Creek marsh have changed significantly over the past ~1,000 years, creating a distinct fining-upward sequence. This sequence preserves the signature (from bottom to top) of subtidal flats grading to intertidal sandflats, an erosional lag created by a migrating tidal channel, point bar deposits, channel fill deposits, and a capping salt marsh. A significant change in environmental conditions occurred between 360–500 cal years BP, which changed the character of geological, geochemical and microfossil components in the marsh, and, because this observation is robust throughout the southeastern US, hints at a major change in estuarine and coastal systems at this time.

Altieri, A.H., van Wesenbeeck, B.K., Bertness, M.D. and Silliman, B.R. 2010. Facilitation cascade explains positive relationship between native biodiversity and invasion success. Ecology. 91:1269-1275. (DOI: 10.1890/09-1301.1)

Abstract
The pervasive impact of invasive species has motivated considerable research to understand how characteristics of invaded communities, such as native species diversity, affect the establishment of invasive species. Efforts to identify general mechanisms that limit invasion success, however, have been frustrated by disagreement between landscape-scale observations that generally find a positive relationship between native diversity and invasibility and smaller-scale experiments that consistently reveal competitive interactions that generate the opposite relationship. Here we experimentally elucidate the mechanism explaining the large-scale positive associations between invasion success and native intertidal diversity revealed in our landscape-scale surveys of New England shorelines. Experimental manipulations revealed this large-scale pattern is driven by a facilitation cascade where ecosystem-engineering species interact nonlinearly to enhance native diversity and invasion success by alleviating thermal stress and substrate instability. Our findings reveal that large-scale diversity–invasion relationships can be explained by small-scale positive interactions that commonly occur across multiple trophic levels and functional groups. We argue that facilitation has played an important but unrecognized role in the invasion of other well studied systems, and will be of increasing importance with anticipated climate change.

Andrus, C.F. and Thompson, V.D. 2012. Determining the Habitats of Mollusk Collection at the Sapelo Island Shell Ring Complex, USA using Oxygen Isotope Sclerochronology. Journal of Archaeological Science. 39:215-228. (DOI: 10.1016/j.jas.2011.08.002)

Abstract
Sequential oxygen isotope analysis was performed on Mercenaria spp. (n = 41) and Crassostrea virginica (n = 17) valves excavated from the Sapelo Island Shell Ring complex, coastal Georgia, USA. The data were analyzed to determine the habitats in which the mollusks were harvested in order to gain insight into the subsistence practices of the site occupants. The rationale for this study is based on the observation that temperatures are similar in all of the habitats surrounding the island, but the δ18Owater trends across the habitats co-vary with salinity. Accordingly, the shells grown in these habitats contain sinusoidal oscillations in δ18O through ontogeny due primarily to seasonal temperature variation, but the absolute values reflect the salinity ranges of each habitat. Assuming a relatively constant oxygen isotope/salinity gradient since the time of site occupation, it appears that both of these mollusks were exploited over nearly the full range of their salinity tolerances. While a precise estimate of travel distance during collection cannot be made, these data suggest that mollusks were harvested at distances from the site greater than would be predicted using terrestrial foraging models. In addition to providing insight into past subsistence strategies in this region, this research establishes a new method of assessing catchment area and mobility practices.

Angelini, C. and Briggs, K. 2015. Spillover of Secondary Foundation Species Transforms Community Structure and Accelerates Decomposition in Oak Savannas. Ecosystems. 18:780-791. (DOI: 10.1007/s10021-015-9862-0)

Abstract
Secondary foundation species facilitate biodiversity by providing complex habitat within the protective structures of many primary foundation species; whether they retain this role when they are dispersed in novel environments is unclear. Here, we explore how secondary foundation species’ density within hosts controls the rate at which individuals accrue and test if dislodged secondary foundation species then bolster the abundance and diversity of associated species and decomposition in a widespread system: southern live oaks, Quercus virginiana, hosting festoons of the bromeliad, Tillandsia usneoides, in southeastern US savannas. One year of monitoring showed that as Tillandsia density within oaks increases, Tillandsia deposition beneath oaks increases linearly in kind. Once on the ground, two manipulative experiments revealed that: on small scales, individual festoons retain moisture, reduce temperature, and facilitate invertebrates and fungi which combine to accelerate litter decomposition and, on larger scales, continual deposition of festoons dramatically reduces grass cover and increases litter layer depth, invertebrate and fungi richness and density, and decomposition. Surveys further suggest that Tillandsia populations within oaks, in moderating festoon accumulation, are shaping understory communities throughout this geographic region. Thus, disturbance-induced spillover enables secondary foundation species to define biodiversity and ecosystem functioning beyond the boundaries of their hosts.

Angelini, C. and Silliman, B.R. 2012. Patch size-dependent community recovery after massive disturbance. Ecology. 93(1):101–110. (DOI: 10.1890/11-0557.1)

Abstract
Massive anthropogenic and climate-related disturbances are now common in ecosystems worldwide, generating widespread die-off and subsequent community recovery dominated by remnant-patch dynamics rather than open-gap dynamics. Whether communities can recover and, if so, which factors mediate recolonization rate and extent remain unresolved. Here we evaluate recolonization dynamics of southern U.S. salt marshes that experienced extensive, drought-induced die-off of the foundation species Spartina alterniflora over the previous decade. Surveys of Georgia (USA) salt marshes showed little seedling recruitment in die-off areas but persistence of Spartina particularly in large, rather than small, remnant patches. Given this natural variation in remnant patch size, we conducted field experiments to test whether key plant-controlling biotic (grazing, plant neighbor presence) and abiotic (water availability) factors differentially impact Spartina recolonization at small and large-patch scales. In the small-patch (,1 m2) experiment in 2009, removing grazers and plant neighbors prompted dramatically higher expansion and growth of Spartina relative to controls, while adding freshwater to reduce water limitation had little effect. In contrast, large-patch (.20 m2) borders advanced significantly over the same time period regardless of grazer or neighbor removal. We continued the large-patch experiments in 2010, a year that experienced drought, and also added freshwater or salt to borders to modify ambient drought stress; overall, borders advanced less than the previous year but significantly more where neighbors were removed or freshwater added. Thus, water availability appears to mediate Spartina recovery by fueling large-patch expansion during wet summers and intensifying interspecific competition during drought. Combined, these findings suggest ecosystems can recover from massive disturbance if remnant foundation species’ patches are large enough to overcome biotic inhibition and successfully expand during periods of relaxed abiotic stress.

Angelini, C. and Silliman, B.R. 2014. Secondary foundation species as drivers of trophic and functional diversity: evidence from a tree-epiphyte system. Ecology. 95(1):185-196.

Abstract
Facilitation cascades arise where primary foundation species facilitate secondary (dependent) foundation species, and collectively, they increase habitat complexity and quality to enhance biodiversity. Whether such phenomena occur in nonmarine systemsand if secondary foundation species enhance food web structure (e.g., support novel feeding guilds) and ecosystem function (e.g., provide nursery for juveniles) remain unclear. Here we report on field experiments designed to test whether trees improve epiphyte survival and epiphytes secondarily increase the number and diversity of adult and juvenile invertebrates in a potential live oak–Tillandsia usneoides (Spanish moss) facilitation cascade. Our results reveal that trees reduce physical stress to facilitate Tillandsia, which, in turn, reduces desiccation and predation stress to facilitate invertebrates. In experimental removals, invertebrate total density, juvenile density, species richness and H0 diversity were 16, 60, 1.7, and 1.5 times higher, and feeding guild richness and H0 were 5 and 11 times greater in Tillandsia-colonized relative to Tillandsia-removal limb plots. Tillandsia enhanced communities similarly in a survey across the southeastern United States. These findings reveal that a facilitation cascade organizes this widespread terrestrial assemblage and expand the role of secondary foundation species as drivers of trophic structure and ecosystem function. We conceptualize the relationship between foundation species’ structural attributes and associated species abundance and composition in a Foundation Species–Biodiversity (FSB) model. Importantly, the FSB predicts that, where secondary foundation species form expansive and functionally distinct structures that increase habitat availability and complexity within primary foundation species, they generate and maintain hot spots of biodiversity and trophic interactions.

Angelini, C., Alteiri, A., Silliman, B.R. and Bertness, M.D. 2011. Interactions among Foundation Species and Their Consequences for Community Organization, Biodiversity, and Conservation. BioScience. 61(10):782-789. (DOI: 10.1525/bio.2011.61.10.8)

Abstract
Foundation species create complex habitats in which associated organisms find refuge from biological and physical stress; these foundation species are thus fundamental to the structure and resilience of terrestrial and marine ecosystems. In the present article, we develop an approach to understanding foundation species' effects in communities that are maintained not by a single foundation species, as has been the focus of research to date, but by multiple, co-occurring foundation species. Using examples from diverse ecosystems, we illustrate the prevalence of multiple-foundation-species assemblages and hypothesize that the nature of foundation-species interactions has important consequences for community structure. We predict where positive and negative interactions among foundation species will occur and suggest that they organize communities hierarchically in nested or adjacent assemblages that underlie landscape-scale patterns in species distribution. Elucidating the predictable nature of foundation-species interactions may be key to understanding and managing the biodiversity and functioning of many ecosystems.

Angelini, C., Crotty, S.M., Sharp, S., Prince, K., Cronk, K., Johnson, E. and Bersoza, A.C. 2018. Foundation species patch configurations mediates biodiversity, stability and multifunctionality. Ecology Letters. (DOI: 10.1111/ele.13146)

Abstract
Foundation species enhance biodiversity and multifunctionality across many systems; however, whether foundation species patch configuration mediates their ecological effects is unknown. In a 6‐month field experiment, we test which attributes of foundation species patch configuration – i.e. patch size, total patch area, perimeter, area‐perimeter ratio, or connectivity – control biodiversity, stability and multifunctionality by adding a standardised density of mussel foundation species in patches of 1, 5, 10, 30, 60, 90 or 180 individuals to a southeastern US salt marsh. Over 67% of response variables increased with clustering of mussels, responses that were driven by increases in area–perimeter ratio (33%), decreases in perimeter (29%), or increases in patch size (5%), suggesting sensitivity to external stressors and/or dependence on foundation species‐derived niche availability and segregation. Thus, mussel configuration – by controlling the relative distribution of multidimensional patch interior and edge niche space – critically modulates this foundation species’ effects on ecosystem structure, stability and function.

Angelini, C., Griffin, J., van de Koppel, J., Derksen-Hooijberg, M., Lamers, L., Smolders, A.J.P., van der Heide, T. and Silliman, B.R. 2016. A keystone mutualism underpins resilience of a coastal ecosystem to drought. Nature Communications. 7:12473. (DOI: 10.1038/ncomms12473)

Abstract
Droughts are increasing in severity and frequency, yet the mechanisms that strengthen ecosystem resilience to this stress remain poorly understood. Here, we test whether positive interactions in the form of a mutualism between mussels and dominant cordgrass in salt marshes enhance ecosystem resistance to and recovery from drought. Surveys spanning 250 km of southeastern US coastline reveal spatially dispersed mussel mounds increased cordgrass survival during severe drought by 5- to 25-times. Surveys and mussel addition experiments indicate this positive effect of mussels on cordgrass was due to mounds enhancing water storage and reducing soil salinity stress. Observations and models then demonstrate that surviving cordgrass patches associated with mussels function as nuclei for vegetative re-growth and, despite covering only 0.1–12% of die-offs, markedly shorten marsh recovery periods. These results indicate that mutualisms, in supporting stress-resistant patches, can play a disproportionately large, keystone role in enhancing ecosystem resilience to climatic extremes.

Angelini, C., van der Heide, J., Griffin, J., Derksen-Hooijberg, M., Lamers, L., Smolders, A.J.P. and Silliman, B.R. 2015. Foundation species' overlap enhances biodiversity and ecosystem multifunctionality from the patch to landscape scale. Proceedings of the Royal Society B. (DOI: 10.1098/rspb.2015.0421)

Abstract
Although there is mounting evidence that biodiversity is an important and widespread driver of ecosystem multifunctionality, much of this research has focused on small-scale biodiversity manipulations. Hence, which mechanisms maintain patches of enhanced biodiversity in natural systems and if these patches elevate ecosystem multifunctionality at both local and landscape scales remain outstanding questions. In a 17 month experiment conducted within southeastern United States salt marshes, we found that patches of enhanced biodiversity and multifunctionality arise only where habitat-forming foundation species overlap--i.e. where aggregations of ribbed mussels (Geukensia demissa) form around cordgrass (Spartina alterniflora) stems. By empirically scaling up our experimental results to the marsh platform at 12 sites, we further show that mussels--despite covering only approximately 1% of the marsh surface--strongly enhance five distinct ecosystem functions, including decomposition, primary production and water infiltration rate, at the landscape scale. Thus, mussels create conditions that support the co-occurrence of high densities of functionally distinct organisms within cordgrass and, in doing so, elevate salt marsh multifunctionality from the patch to landscape scale. Collectively, these findings suggest that patterns in foundation species' overlap drive variation in biodiversity and ecosystem functioning within and across natural ecosystems.We therefore argue that foundation species should be integrated in our conceptual understanding of forces that moderate biodiversity--ecosystem functioning relationships, approaches for conserving species diversity and strategies to improve the multifunctionality of degraded ecosystems.

Angelini, C., van Montfrans, S., Hensel, M.S., He, Q. and Silliman, B.R. 2018. The importance of an underestimated grazer under climate change: how crab density, consumer competition, and physical stress affect salt marsh resilience. Oecologia. 187(1):205-217. (DOI: 10.1007/s00442-018-4112-8)

Abstract
Climate change and consumer outbreaks are driving ecosystem collapse worldwide. Although much research has demonstrated that these factors can interact, how heterogeneity in top–down control intensity and physical forcing modulates ecosystem resilience to climate stress remains poorly understood. Here, we explore whether the nocturnal herbivorous crab Sesarma reticulatum can control spatially dominant cordgrass (Spartina alterniflora) growth and how its top–down effects vary with crab density, drought stress, and large-scale disturbance in southeastern US salt marshes. In multiple field experiments and surveys, we show that Sesarma depresses cordgrass growth and that its effects increase in a saturating manner with increasing crab density, such that the highest naturally occurring densities of this consumer can trigger local cordgrass die-off. This top–down effect of Sesarma is similar in magnitude to what is thought to be the dominant grazer in the system, the marsh periwinkle snail Littoraria irrorata. In a drought stress by Sesarma density experiment, we further show that salinity stress and intensive crab herbivory additively suppress cordgrass drought resistance. After drought subsides, surveys and experiments reveal that Sesarma also stifles cordgrass re-growth into existing die-off areas. Together, these results show that multiple grazers powerfully regulate the productivity and drought resilience of these intertidal grasslands and that heterogeneity in physical stress and consumer density can dictate when and where top–down forcing is important. More generally, this work provides a rare, experimental demonstration of the critical role top–down control can play across the initiation and recovery stages of ecosystem die-off.

Aretxabaleta, A., Nelson, J.R., Blanton, J.O., Seim, H.E., Werner, F.E., Bane, J.M. and Weisberg, R. 2006. Cold event in the South Atlantic Bight during summer of 2003: Anomalous hydrographic and atmospheric conditions. Journal of Geophysical Research. 111:C06007. (DOI: 10.1029/2005JC003105)

Abstract
Unusually cold seawater temperatures were observed along much of the U.S. eastern seaboard during the summer of 2003. In this study, hydrographic and atmospheric observations from spring through summer were analyzed to track the evolution of the cold water event in the South Atlantic Bight (SAB) and investigate links to various forcing mechanisms. The hydrographic observations included 13 cross-shelf transects over the central region of the SAB, surface temperature time series from several NDBC stations, and bottom temperatures from a mid shelf mooring. Atmospheric data were obtained from NDBC stations. Additional data included water level from NOS stations and river discharge from USGS stations. The conditions observed during spring and summer of 2003 were compared with climatological values. Record precipitation and increased river discharge during spring produced strong salinity stratification over the inner and mid shelf. Anomalously intense and persistent upwelling-favorable winds were present from May until August. On the mid and outer shelf the resulting upwelling and subsurface shoreward penetration of cold water acted as a feedback mechanism to preserve the stratified conditions through the summer. The characteristics of the upwelled water corresponded to water from the lower part of the Gulf Stream water column. On the shelf the resulting temperature values under the thermocline were significantly lower than climatological temperatures by 5°–7°C.

Atkins, R., Griffin, J.N., Angelini, C., O'Connor, M. and Silliman, B.R. 2015. Consumer- plant interaction strength: importance of body size, density and metabolic biomass. OIKOS. (DOI: 10.1111/oik.01966)

Abstract
Explaining variability in the strength and sign of trophic interactions between primary consumers and plants is a long-standing research challenge. Consumer density and body size vary widely in space and time and are predicted to have interactive effects on consumer–plant interactions. In a southern US salt marsh, we used replicate field enclosures to orthogonally manipulate the body size (mass) and density of a dominant consumer (a snail). We investigated impacts (leaf damage and biomass) on monocultures of cordgrass, the foundation species, over three months. Increasing consumer density and body size increased leaf damage additively and, as predicted, multiplicatively reduced plant biomass. Notably, size and density determined the sign of consumer impact on plants: low to medium densities of small consumers enhanced, while high densities of large consumers strongly suppressed plant biomass. Finally, total consumer metabolic biomass (mass0.75) within an enclosure parsimoniously explained plant biomass response, supporting theoretical predictions and suggesting that multiplicative effects of density and body size resulted from their effects on total metabolic biomass. The consequences of changes in consumer density and body size resulting from anthropogenic perturbations may therefore be predicted based on metabolic biomass.

Baas, P., Hester, M. and Joye, S.B. 2014. Benthic primary production and nitrogen cycling in Spartina alterniflora marshes: effect of restoration after acute dieback. Biogeochemistry. 117(2-3):511-524. (DOI: 10.1007/s10533-013-9897-2)

Abstract
The sudden and massive Spartina alterniflora dieback at the turn of the millennium generated numerous unanswered questions regarding its mechanistic causes and consequences. This study, conducted during 2007–2008, aimed to elucidate mechanisms of recovery and determine whether recovery was accelerated by replanting efforts. The onset of a severe drought during the summer of 2007, however, provided a potential glimpse into the mechanisms driving dieback events. Study sites were established in two of the hardest hit states, Georgia and Louisiana. Each site had a replicated block design consisting of the following four treatments: reference, dieback, dieback with low density replanting (90 cm spacing), and dieback with high density replanting (30 cm spacing). To assess biogeochemical cycling and ecosystem functioning, we quantified rates of nitrogen fixation, potential nitrification, potential denitrification, and benthic production biannually. All measured process rates decreased following the drought year of 2007. Nitrogen fixation was positively correlated with benthic production rates in Louisiana, while denitrification was positively correlated with benthic production rates in Georgia and Louisiana. The lack of decreased benthic production during the 2007 drought could indicate that benthic microphytes cope with better with drought than plants, but may be outcompeted during non-drought years. Replanting efforts significantly increased ecosystem recovery in Louisiana and to a lesser extent in Georgia.

Barbier, E.B., Hacker, S.D., Koch, E.W., Stier, A. and Silliman, B.R. 2011. The Value of Estuarine and Coastal Ecosystem Services. Ecological Monographs. 81:169-193.

Abstract
The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat–fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat–fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land–sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

Bauer, J., Cai, W.-J., Raymond, P., Bianchi, T.S., Hopkinson, C.S. and Regnier, P.A.G. 2013. The changing carbon cycle of the coastal ocean. Nature. 504:61-70. (DOI: 10.1038/nature12857)

Abstract
The carbon cycle of the coastal ocean is a dynamic component of the global carbon budget. But the diverse sources and sinks of carbon and their complex interactions in these waters remain poorly understood. Here we discuss the sources, exchanges and fates of carbon in the coastal ocean and how anthropogenic activities have altered the carbon cycle. Recent evidence suggests that the coastal ocean may have become a net sink for atmospheric carbon dioxide during post-industrial times. Continued human pressures in coastal zones will probably have an important impact on the future evolution of the coastal ocean's carbon budget.

Bertness, M.D. and Silliman, B.R. 2008. Consumer Control of Salt Marshes Driven by Human Disturbance. Conservation Biology. 22(3):618-623. (DOI: 10.1111/j.1523-1739.2008.00962.x)

Abstract
Salt marsh ecosystems are widely considered to be controlled exclusively by bottom–up forces, but there is mounting evidence that human disturbances are triggering consumer control in western Atlantic salt marshes, often with catastrophic consequences. In other marine ecosystems, human disturbances routinely dampen (e.g., coral reefs, sea grass beds) and strengthen (e.g., kelps) consumer control, but current marsh theory predicts little potential interaction between humans and marsh consumers. Thus, human modification of top–down control in salt marshes was not anticipated and was even discounted in current marsh theory, despite loud warnings about the potential for cascading human impacts from work in other marine ecosystems. In spite of recent experiments that have challenged established marsh dogma and demonstrated consumer-driven die-off of salt marsh ecosystems, government agencies and nongovernmental organizations continue to manage marsh die-offs under the old theoretical framework and only consider bottom–up forces as causal agents. This intellectual dependency of many coastal ecologists and managers on system-specific theory (i.e., marsh bottom–up theory) has the potential to have grave repercussions for coastal ecosystem management and conservation in the face of increasing human threats. We stress that marine vascular plant communities (salt marshes, sea grass beds, mangroves) are likely more vulnerable to runaway grazing and consumer-driven collapse than is currently recognized by theory, particularly in low-diversity ecosystems like Atlantic salt marshes.

Bhatti, A., Rundquist, D., Schalles, J.F., Ramirez, L. and Nasu, S. 2009. A comparision between above-water surface and subsurface spectral reflectances collected over inland waters. GeoCarto International. 24(2):133-141. (DOI: 10.1080/10106040802460707)

Abstract
The objective of the research was to undertake a quantitative comparison of spectral reflectance measurements made slightly above the surface of water bodies with themeasurements made slightly below the surface. The study is focused on three rivers; two in Georgia, USA and one in Japan. As expected, the differences in reflectance are not constant and vary with the wavelength. The contribution of surface-reflection effects to the surface reflectance measured slightly above the water is both pronounced and highlyvariable, but while they do alter the magnitude of the upwelling signal, they do notchange the general shape of the spectral profiles. The correction of surface-reflectioneffects by assuming a proportionality factor (ρ) is not considered to be efficient forinland fresh water bodies. For in-situ spectroscopy, the recommended approach is tomeasure upwelling radiance slightly below the water’s surface as a means of minimizingextraneous noise. Researchers should be aware of the potential for diminishing thevalidity of findings because of measurement errors.

Biers, E.J., Zepp, R.G. and Moran, M.A. 2007. The role of nitrogen in chromophoric and fluorescent dissolved organic matter formation. Marine Chemistry. 103:46-60. (DOI: 10.1016/j.marchem.2006.06.003)

Abstract
Microbial and photochemical processes affect chromophoric dissolved organic matter (CDOM) dynamics in the ocean. Some evidence suggests that dissolved nitrogen plays a role in CDOM formation, although this has received little systematic attention in marine ecosystems. Coastal seawater incubations were carried out in the presence of model dissolved organic nitrogen (DON: amino sugars and amino acids) and dissolved inorganic nitrogen (DIN) compounds to assess their role in biological and photochemical production of CDOM. For several of the dissolved N compounds, microbial processing resulted in a pulse of CDOM that was mainly labile, appearing and disappearing within 7 days. In contrast, a net loss of CDOM occurred when no N was added to the microbial incubations. The greatest net biological CDOM formation was found upon addition of amino sugars (formation of fluorescent, mostly labile CDOM) and tryptophan (formation of non-fluorescent, refractory CDOM). Photochemical formation of CDOM was only found with tryptophan, the one aromatic compound tested. This CDOM was highly fluorescent, with excitation–emission matrices (EEMs) resembling those of terrestrial, humic-like fluorophores. The heterogeneity in CDOM formation from this collection of labile N-containing compounds was surprising. These compounds are common components of biopolymers and humic substances in natural waters and likely to contribute to microbially- and photochemically-produced CDOM in coastal seawater

Bishop, T.D., Miller, H.L. III, Walker, R.L., Hurley, D., Menken, T. and Tilburg, C.E. 2010. Blue crab (Callinectes sapidus Rathbun, 1896) settlement at three Georgia (USA) estuarine sites. Estuaries and Coasts. 33:688-698. (DOI: 10.1007/s12237-009-9259-4)

Abstract
The blue crab, Callinectes sapidus Rathbun, 1896, represents the second most important fishery for coastal Georgia; yet, little is known about environmental forces that affect planktonic postlarval settlement in the region. Here, we describe a study to examine the physical mechanisms responsible for blue crab settlement in the extensive salt marsh system of coastal Georgia. Bottom and surface samplers were placed at three sites along a salinity gradient from a low-salinity site in the Altamaha River to a high-salinity area of the Duplin River, Sapelo Island, GA, USA during 2005. Megalopae and juvenile monitoring occurred from July through December. The majority of both megalopae (86.8%) and juvenile (89.3%) blue crabs were recovered in bottom samplers at the low-salinity Altamaha River site during August and early September. Few megalopae were collected at the surface of the Altamaha River or at the two higher-salinity sites in the Duplin and North Rivers. Downwelling winds were unable to explain all settlement events; however, winds with an onshore component regularly preceded settlement events. The use of a multiple-regression model revealed a lagged relationship (r = 0.5461, lag = 0–2 days) between wind events, temperature, salinity, maximum tidal height, and settlement.

Blanton, J.O. and Andrade, F.A. 2001. Distortion of tidal currents and the lateral transfer of salt in a shallow coastal plain estuary. Estuaries. 24:467-480.

Abstract
We describe the tidal circulation of a coastal plain estuary across a flood tide delta located at its entrance. The area connects the downstream portion of the main estuary extending 30-40km inland to the more complex delta reach that consists of a shallow main channel and a series of smaller side channels. The delta acts as a frictionally dominated zone that modifies the tidal wave from a simple sinusoid to one with ebb currents that accelerate to maximum early in the tidal cycle and last more than one-half of the tidal cycle. Along smaller side channels, the tidal currents favor stronger flood or ebb currents, depending upon the local surrounding morphology. The phase difference between ebb currents in the small channels relative to those in the main channel cause some of the salt to be retained thus reducing the tendency of freshwater discharge to flush salt out of the system. This mechanism of retention differs from the selective withdrawal mechanism described for this estuary in Blanton et al. (2000).

Blanton, J.O., Andrade, F.A. and Ferreira, M.A. 2000. Effect of a broad shallow sill on the tidal circulation and salt transport in the entrance to a coastal plain estuary (Mira - Vila Nova de Milfontes, Portugal). Estuaries. 23:293-304.

Abstract
The dynamics of tidal intrusion fronts across sills and selective withdrawal (aspiration) in deeper channels control the exchange of seawater with the estuary. During neap tide and strong vertical stratification, flooding seawater plunges beneath less dense estuarine water somewhere on the sill. Turbulence on the sill in the intruding bottom layer promotes entrainment of fluid from the surface layer, and seawater along the sill bottom is diluted with estuarine water. Ebb flow effectively traps high salinity landward of the sill in a stagnant zone between the aspiration depth and the bottom, where it can be advected farther upstream by subsequent flood currents. During spring tide, the plunge point moves landward and off the sill, stratification is weakened in the deep channel, and aspiration during ebb extends to the bottom. This prevents the formation of stagnant water near the bottom, and the estuary is flooded with high salinity water far inland. The neap-spring cycle of tidal intrusion fronts on flood coupled with aspiration during ebb interacts with sills at the entrances of estuaries to play an important role in the transport and retention of salt within the estuary.

Blanton, J.O., Garrett, A., Bollinger, J., Hayes, D., Koffman, L. and Amft, J. 2009. Transport and dispersion of a conservative tracer in coastal waters with large intertidal areas. Estuaries and Coasts. 32:573-592. (DOI: DOI 10.1007/s12237-009-9141-4)

Abstract
In late December 1991, an accidental release of 5,700 CI of tritiated water (HTO) from the Savannah River Site was transported via site streams into the Savannah River where it was carried downstream to the coastal zone. HTO released into a semitropical Georgia estuary was forced into the tidal marshes surrounding the estuary as well as discharged directly into the Atlantic Ocean. The spreading of HTO was studied with a 3D hydrodynamic model (ALGE) that includes flooding and draining of intertidal areas. Comparisons of model simulations to measured HTO concentration showed that ALGE simulated well the general increase and decrease of HTO as its plume passed a given area. The “sheet flow” approximation for marsh and small tidal creek flow largely compensated for lack of model resolution and accurate bathymetry in areas with numerous small to medium-sized tidal creeks. The water volume of the unresolved tidal creeks had to be accounted for in the simulations by increasing the initial water depth over the marshes. ALGE and a simple box model both reproduced the trapping of HTO in intertidal areas. The time scale over which intertidal areas import and export HTO back to the tidal channels varies between 10 and 30 days.

Blanton, J.O., Garrett, A., Bollinger, J., Hayes, D., Koffman, L., Amft, J. and Moore, T.C. 2010. Transport and retention of a conservative tracer in an isolated creek–marsh system. Estuarine, Coastal and Shelf Science. 87:333-345. (DOI: 10.1016/j.ecss.2010.01.010)

Abstract
A study of tracer transport and retention in a small tidal creek and marsh system located in the southeastern US was conducted using a three-dimensional hydrodynamic model and data from a dye tracer release. The model simulated tidally driven flow, including inundation and drying out of the marshes and the dispersal of the dye tracer. Flow measurements in the tidal creek showed that the simulations appeared to generally duplicate the tidally driven flow into and out of the tidal creeks and marshes. The dye tracer experiment was conducted to test the hydrodynamic model’s ability to simulate dispersal of a point release of pollutants into the creek during an incoming tide. The simulations reproduced much of the experimental measurements, but bathymetric errors and lack of resolution of the smallest arms of the tidal creeks affected the ability to faithfully reproduce the initial peak in measured dye tracer concentrations at a sampling location far from the boundary. The lack of the smallest tidal creeks led to some trapping of water and dye in the marshes. Two independent estimates of flushing time yielded values between 1.6 and 2.4 days. An uncertainty analysis indicates that model simulations are sensitive to variations in parameters such as water depth and marsh grass density. On the other hand, omission of the smallest tidal creeks in simulations may be partially offset by decreasing marsh grass density. Further improvements must rely on more accurate and detailed bathymetric data that resolves the smaller arms of the tidal creeks and includes quantitative information about the density and distribution of marsh grass.

Blanton, J.O., Lin, G. and Elston, S.A. 2002. Tidal current asymmetry in shallow estuaries and tidal creeks. Continental Shelf Research. 22:1731-1743.

Abstract
We examine tidal asymmetry in a 100-km long coastal plain estuary, a 15-km long tidal creek closed at the end, and a small side channel of a coastal plain estuary closed at low water. Current meter and water depth data were harmonically analyzed for M2 and the M4 and M6 overtide. The results are displayed in a plot of tidal current versus water level and the effects of the M2, M2+M4, and M2+M4+M6 are compared in order to show how overtides affect tidal asymmetry in the different systems. The long estuary showed a gradual increase in tidal current asymmetry. The current takes on a more progressive nature as it goes into the estuary, as indicated by increasing lags between high or low water and the corresponding slack water. On the other hand, the tidal creek has its reflection point at the head, a relatively short distance from the observations, which reflects the incident tidal wave more efficiently. The tidal creek has a high salt marsh which is covered only an hour or so before high water. Since its intertidal areas flood and drain near the time of high water, maximum flood and ebb currents occur a short time before and after high water slack throughout the tidal creek. Most of the tidal energy is dissipated at the end of the creek where M6/M2 of the tidal current almost doubles. The small side channel has tidal flats that become covered soon after the time of low water. The relative time of maximum flood and ebb currents occurs much closer to the time of low-water-slack, which contrasts significantly to the timing in the tidal creek channel surrounded by high salt marsh.

Blanton, J.O., Seim, H.E., Alexander, C., Amft, J. and Kineke, G. 2003. Transport of salt and suspended sediments in a curving channel of a coastal plain estuary: Satilla River, GA. Estuarine, Coastal and Shelf Science. 57:993-1006.

Abstract
This study describes the transport of salt and suspended sediment in a curving reach of a shallow mesotidal coastal plain estuary. Circulation data revealed a subtidal upstream bottom flow during neap tide, indicating the presence of a gravitational circulation mode throughout the channel. During spring tide, landward bottom flow weakened considerably at the upstream end of the channel and changed to seaward in the middle and downstream areas of the reach, suggesting the importance of tidal pumping. Salt flux near-bottom was landward at both ends of the channel during neap tide. At spring, however, the salt flux diverged along the bottom of the thalweg suggesting that tidal pumping caused a transfer of salt vertically and laterally into the intertidal zone. Thus, landward flux of salt is maintained even in the presence of subtidal seaward flow along the bottom at the downstream end of the channel. Landward bottom stress is greater than seaward stress, preferentially transporting suspended sediments upstream. Compared with salt, however, the weight of the suspended sediments causes less upward transfer of sediments into the intertidal zone. Flood flow carried more suspended sediments landward at the upstream end compared with the downstream end. We speculate that secondary flow in the curving channel picks up increasing amounts of suspended sediments along the sides during flood and adds them to the axial flow in the thalweg. Since the landward flow along the bottom of the thalweg weakens and even reverses during spring tide, there appears to be a complex re-circulation system for sediments re-suspended in curving channels that complicates the picture of a net transport of sediments landward.

Borst, A., van der Heide, T., Verbeek, W., Schotanus, J., Christianen, M., Derksen-Hooijberg, M. and Angelini, C. 2018. Foundation species enhance food web complexity through non-trophic facilitation. PloS ONE. (DOI: 10.1371/journal.pone.0199152)

Abstract
Food webs are an integral part of every ecosystem on the planet, yet understanding the mechanisms shaping these complex networks remains a major challenge. Recently, several studies suggested that non-trophic species interactions such as habitat modification and mutualisms can be important determinants of food web structure. However, it remains unclear whether these findings generalize across ecosystems, and whether non-trophic interactions affect food webs randomly, or affect specific trophic levels or functional groups. Here, we combine analyses of 58 food webs from seven terrestrial, freshwater and coastal systems to test (1) the general hypothesis that non-trophic facilitation by habitat-forming foundation species enhances food web complexity, and (2) whether these enhancements have either random or targeted effects on particular trophic levels, functional groups, and linkages throughout the food web. Our empirical results demonstrate that foundation species consistently enhance food web complexity in all seven ecosystems. Further analyses reveal that 15 out of 19 food web properties can be well-approximated by assuming that foundation species randomly facilitate species throughout the trophic network. However, basal species are less strongly, and carnivores are more strongly facilitated in foundation species' food webs than predicted based on random facilitation, resulting in a higher mean trophic level and a longer average chain length. Overall, we conclude that foundation species strongly enhance food web complexity through non-trophic facilitation of species across the entire trophic network. We therefore suggest that the structure and stability of food webs often depends critically on non-trophic facilitation by foundation species.

Brittain, R. and Craft, C.B. 2012. Effects of Sea-Level Rise and Anthropogenic Development on Priority Bird Species Habitats in Coastal Georgia, USA. Environmental Management. 49:473-482. (DOI: 10.1007/s00267-011-9761-x)

Abstract
We modeled changes in area of five habitats, tidal-freshwater forest, salt marsh, maritime shrub-scrub (shrub), maritime broadleaf forest (oak) and maritime narrowleaf (pine) forest, in coastal Georgia, USA, to evaluate how simultaneous habitat loss due to predicted changes in sea level rise (SLR) and urban development will affect priority bird species of the south Atlantic coastal plain by 2100. Development rates, based on regional growth plans, were modeled at 1% and 2.5% annual urban growth, while SLR rates, based on the Intergovernmental Panel on Climate Change’s A1B mean and maximum scenarios, were modeled at 52 cm and 82 cm, respectively. SLR most greatly affected the shrub habitat with predicted losses of 35–43%. Salt marsh and tidal forest also were predicted to lose considerable area to SLR (20–45 and 23–35%, respectively), whereas oak and pine forests had lesser impact from SLR, 18–22% and 11–15%, respectively. Urban development resulted in losses of considerable pine (48–49%) and oak (53–55%) habitat with lesser loss of shrub habitat (21–24%). Under maximum SLR and urban growth, shrub habitat may lose up to 59–64% compared to as much as 62–65% pine forest and 74–75% oak forest. Conservation efforts should focus on protection of shrub habitat because of its small area relative to other terrestrial habitats and use by Painted Buntings (Passerina ciris), a Partners In Flight (PIF) extremely high priority species. Tidal forests also deserve protection because they are a likely refuge for forest species, such as Northern Parula and Acadian Flycatcher, with the decline of oak and pine forests due to urban development.

Brittain, R., Meretsky, V.J. and Craft, C.B. 2010. Avian communities of the Altamaha River estuary in Georgia, USA. The Wilson Journal of Ornithology. 122(3):532–544. (DOI: 10.1676/09-186.1)

Abstract
We surveyed male breeding birds in five habitats (bottomland forest, maritime oak [Quercus spp.], pine [Pinus spp.] forest, maritime shrub, saltmarsh) of coastal Georgia, USA using distance-sampling methods to estimate population densities. We examined species-habitat relationships using indicator species analysis (ISA). Acadian Flycatcher (Empidonax virescens) in bottomland forest, Northern Parula (Parula americana) in maritime oak, Brown-headed Nuthatch (Sitta pusilla) in pine forest, Clapper Rail (Rallus longirostris) in saltmarsh, and White-eyed Vireo (Vireo griseus) in shrub habitat ranked highest for Partners in Flight (PIF) priority species by densities. The ISA indicated fewer PIF priority species were associated with saltmarsh, but more species (6) were unique to saltmarsh than any other habitat. Indicator species occurred more often in maritime oak than bottomland forest (8 vs. 6), but both habitats had similar numbers of PIF priority species (4). Shrub habitat covered the smallest area (,0.2%) and had three PIF priority species, including Painted Bunting (Passerina ciris), the only PIF species with extremely high priority in this study.

Brittain, R., Schimmelmann, A., Parkhurst, D. and Craft, C. 2012. Habitat Use by Coastal Birds Inferred from Stable Carbon and Nitrogen Isotopes. Estuaries and Coasts. 35:633-645.

Abstract
Conservationists need to know the degree of habitat fidelity for species of conservation concern. Stable Isotope Analysis in R quantified the contribution of terrestrial vs. saltmarsh primary production sources to terrestrial passerine food webs from four habitats of Sapelo Island, Georgia (USA), saltmarsh, maritime scrub–shrub, maritime broadleaf (oak), and maritime narrowleaf (pine) forests, using delta-13C and delta-15N. Models suggested Northern Parula (Parula americana) in oak forests, White-eyed Vireos (Vireo griseus) in shrub, and Brown-headed Nuthatches (Sitta pusilla) in pine forests derived most of their food from habitats they occupied (53–100%). Saltmarsh provided 47–94% of Painted Bunting (Passerina ciris) food sources, supporting previous findings by Springborn and Meyers (2005). Thus, Painted Bunting conservation in the Southeastern USA should focus on Springborn and Meyers' suggestion of maritime scrub–shrub habitat and forests with <75% canopy, >50% ground cover, and patches of shrubs that are within 700 m of saltmarsh.

Bromberg-Gedan, K. and Silliman, B.R. 2009. Using Facilitation Theory to Enhance Mangrove Restoration. Ambio. 38(2):109.

Abstract
Despite advances in positive interactions and facilitation theory in ecological research (1, 2), the concepts have failed to make a big impact on mangrove restoration ecology. Restoration applications of facilitation include reaping the community benefits of foundation species, positive density dependence, and facilitation cascades (3). In their June 2008 article, ‘‘Growth Performance of Planted Mangroves in the Philippines: Revisiting Forest Management Strategies,’’ Samson and Rollon discuss failed mangrove restoration projects in the Philippines and suggest that the poor growth and mortality of Rhizophora spp. seedlings were due to inappropriate placement of seedlings in low intertidal mudflat and seagrass habitats, instead of being planted in existing or deforested mangrove areas (many of which are now privately controlled). Planting mangrove seedlings at appropriate elevations to limit abiotic stress on seedlings is a major tenet of recent mangrove restoration work (4), and Samson and Rallon expand on this to say it must be the primary focus of future efforts if restoration is to succeed. This conclusion is overly narrow, whereas incorporating positive interactions into restoration practices will be complementary to ongoing approaches and result in mangrove forest restoration efforts having greater success under a wider range of environmental conditions.

Bromberg-Gedan, K., Kirwan, M., Barbier, E.B., Wolanski, E. and Silliman, B.R. 2011. The present and future role of coastal wetland vegetation in protecting shorelines: answering recent challenges to the paradigm. Climatic Change. 106:7-29.

Abstract
For more than a century, coastal wetlands have been recognized for their ability to stabilize shorelines and protect coastal communities. However, this paradigm has recently been called into question by small-scale experimental evidence. Here, we conduct a literature review and a small meta-analysis of wave attenuation data, and we find overwhelming evidence in support of established theory. Our review suggests that mangrove and salt marsh vegetation afford context-dependent protection from erosion, storm surge, and potentially small tsunami waves. In biophysical models, field tests, and natural experiments, the presence of wetlands reduces wave heights, property damage, and human deaths. Meta-analysis of wave attenuation by vegetated and unvegetated wetland sites highlights the critical role of vegetation in attenuating waves. Although we find coastal wetland vegetation to be an effective shoreline buffer, wetlands cannot protect shorelines in all locations or scenarios; indeed large-scale regional erosion, river meandering, and large tsunami waves and storm surges can overwhelm the attenuation effect of vegetation. However, due to a nonlinear relationship between wave attenuation and wetland size, even small wetlands afford substantial protection from waves. Combining man-made structures with wetlands in ways that mimic nature is likely to increase coastal protection. Oyster domes, for example, can be used in combination with natural wetlands to protect shorelines and restore critical fishery habitat. Finally, coastal wetland vegetation modifies shorelines in ways (e.g. peat accretion) that increase shoreline integrity over long timescales and thus provides a lasting coastal adaptation measure that can protect shorelines against accelerated sea level rise and more frequent storm inundation. We conclude that the shoreline protection paradigm still stands, but that gaps remain in our knowledge about the mechanistic and context-dependent aspects of shoreline protection.

Bromberg-Gedan, K., Silliman, B.R. and Bertness, M.D. 2009. Centuries of human-driven change in salt marsh ecosystems. Annual Review of Marine Science. 1:117-141. (DOI: 10.1146/annurev.marine.010908.163930)

Abstract
Salt marshes are among the most abundant, fertile, and accessible coastal habitats on earth, and they provide more ecosystem services to coastal populations than any other environment. Since the Middle Ages, humans have manipulated salt marshes at a grand scale, altering species composition, distribution, and ecosystem function. Here, we review historic and contemporary human activities in marsh ecosystems—exploitation of plant products; conversion to farmland, salt works, and urban land; introduction of non-native species; alteration of coastal hydrology; and metal and nutrient pollution. Unexpectedly, diverse types of impacts can have a similar consequence, turning salt marsh food webs upside down, with dramatic consumer control replacing bottom-up control, the long-accepted regulating force. Of the various impacts, invasive species, runaway consumer effects, and sea level rise represent the greatest threats to salt marsh ecosystems.We conclude that the best way to protect salt marshes and the services they provide is through the integrated approach of ecosystem-based management.

Buchan, A., Newell, S.Y., Butler, M., Biers, E.J., Hollibaugh, J.T. and Moran, M.A. 2003. Dynamics of bacterial and fungal communities on decaying salt marsh grass. Applied and Environmental Microbiology. 69:6676-6687.

Abstract
Both bacteria and fungi play critical roles in decomposition processes in many natural environments, yet only rarely have they been studied as an integrated microbial community. Here we describe the bacterial and fungal assemblages associated with two decomposition stages of Spartina alterniflora detritus in a productive southeastern U.S. salt marsh. 16S rRNA genes and 18S-to-28S internal transcribed spacer (ITS) regions were used to target the bacterial and ascomycete fungal communities, respectively, based on DNA sequence analysis of isolates and environmental clones and by using community fingerprinting based on terminal restriction fragment length polymorphism (T-RFLP) analysis. Seven major bacterial taxa (six affiliated with the alpha-Proteobacteria and one with the Cytophagales) and four major fungal taxa were identified over five sample dates spanning 13 months. Fungal terminal restriction fragments (T-RFs) were informative at the species level; however, bacterial T-RFs frequently comprised a number of related genera. Amplicon abundances indicated that the salt marsh saprophyte communities have little-to-moderate variability spatially or with decomposition stage, but considerable variability temporally. However, the temporal variability could not be readily explained by either successional shifts or simple relationships with environmental factors. Significant correlations in abundance (both positive and negative) were found among dominant fungal and bacterial taxa that possibly indicate ecological interactions between decomposer organisms. Most associations involved one of four microbial taxa: two groups of bacteria affiliated with the alpha-Proteobacteria and two ascomycete fungi (Phaeosphaeria spartinicola and environmental isolate "4clt").

Buchan, A., Newell, S.Y., Moreta, J.I.L. and Moran, M.A. 2002. Analysis of Internal Transcribed Spacer (ITS) Regions of rRNA Genes in Fungal Communities of a Southeastern U. S. Salt Marsh. Microbial Ecology. 43:329-340.

Abstract
The ascomycete community colonizing decaying Spartina alterniflora blades in a southeastern U.S. salt marsh was characterized by analysis of internal transcribed spacer (ITS) regions of fungal rRNA genes. ITS sequences were amplified with ascomycete-specific primers from DNA extracted from S. alterniflora blades at two stages of decay (early and late), and were identified based on sequence analysis of a companion ascomycete culture collection. The S. alterniflora ITS libraries were dominated by clones from three species of ascomycetes: Mycosphaerella sp. 2, Phaeosphaeria spartinicola, and Phaeosphaeria halima. ITS sequences from five other less abundant ascomycete species were also found in the clone libraries, only two of which could be identified based on the culture collection, Hydropisphaera erubescens and a new species nicknamed '4clt'. Ascospore expulsion assays indicated dominance by the same three species as the ITS analysis, although this non-molecular approach differed from the molecular method in relative ranking of the dominant species and in characterization of minor species. Analysis of ITS amplicons from three replicate plots by terminal restriction fragment length polymorphism (T-RFLP) analysis showed significant spatial homogeneity in ascomycete community composition for both early and late stage decay. ITS sequence analysis identified morphologically cryptic subgroups for two of the three dominant salt marsh ascomycetes.

Buck, T.L., Breed, G.A., Pennings, S.C., Chase, M.E., Zimmer, M. and Carefoot, T.H. 2003. Diet choice in an omnivorous salt marsh crab: different food types, claw allometry, and habitat complexity. Journal of Experimental Marine Biology and Ecology. 292:103-116.

Abstract
Studies of diet choice by omnivores have the potential to form conceptual links between studies of diet choice by herbivores, frugivores, detritivores, and predators. We examined diet choice in the omnivorous salt marsh crab Armases cinereum ( = Sesarma cinereum (Grapsidae)) in a series of laboratory experiments. Armases is sexually dimorphic, with larger males having relatively larger claws than females. In a growth experiment, an invertebrate diet supported better growth than any other single diet; however, growth also occurred on single diets of mud, leaf litter or fresh leaves. Mixed diets provided the best growth. If alternative foods were available, consumption of leaf litter and fresh leaves decreased, but these items were not dropped from the diet completely. In contrast, consumption of invertebrate prey was not affected by the availability of alternative foods. In a predation experiment, crustacean prey (an amphipod and an isopod) were more vulnerable to predation by Armases than were two small gastropod species. Only large male Armases were able to consume large numbers of gastropods. Environmental structure (plant litter or litter mimics) reduced predation rates, especially on crustaceans, which actively utilized the structure to hide from predators. Armases consumes a mixed diet because several factors (prey physical defenses, avoidance behavior of prey, growth benefits of a mixed diet) favor omnivory over a specialized diet.

Burns, C., Alber, M. and Alexander, C.R. Jr. 2020. Historical Changes in the Vegetated Area of Salt Marshes. Estuaries and Coasts. (DOI: https://doi.org/10.1007/s12237-020-00781-6)

Abstract
Salt marshes are valuable ecosystems, and there is concern that increases in the rate of sea level rise along with anthropogenic activities are leading to the loss of vegetated habitat. The area of vegetated marsh can change not only through advance and retreat of the open fetch edge, but also due to channel widening and contracting, formation and drainage of interior ponds, formation and revegetation of interior mud flats, and marsh migration onto upland areas, each of which is influenced by different processes. This study used historical aerial photographs to measure changes in the extent of vegetated marsh over approximately 70 years at study marshes located in three long-term ecological research (LTER) sites along the US East coast: Georgia Coastal Ecosystems (GCE), Virginia Coast Reserve (VCR), and Plum Island Ecosystems (PIE). Marsh features were categorized into vegetated marsh, ponds, interior mud flats, and channels for three time periods at each site. The three sites showed different patterns of change in vegetated marsh extent over time. At the GCE study site, losses in vegetated marsh, which were primarily due to channel widening, were largely offset by channel contraction in other areas, such that there was little to no net change over the study period. The study marsh at VCR experienced extensive vegetated marsh loss to interior mud flat expansion, which occurred largely in low-lying areas. However, this loss was counterbalanced by marsh gain due to migration onto the upland, resulting in a net increase in vegetated marsh area over time. Vegetated marsh at PIE decreased over time due to losses from ponding, channel widening, and erosion at the open fetch marsh edge. Digital elevation models revealed that the vegetated areas of the three marshes were positioned at differing elevations relative to the tidal frame, with PIE at the highest and VCR at the lowest elevation. Understanding the patterns of vegetation loss and gain at a given site provides insight into what factors are important in controlling marsh dynamics and serves as a guide to potential management actions for marsh protection.

Caffrey, J.M., Bano, N., Kalanetra, K. and Hollibaugh, J.T. 2007. Ammonia oxidation and ammonia-oxidizing Bacteria and Archaea populations from estuaries with differing histories of hypoxia. ISME Journal. 1:660-662. (DOI: 10.1038/ismej.2007.79)

Abstract
Nitrification, the oxidation of NH4+ to NO2- and subsequently to NO3-, plays a central role in the nitrogen cycle and is often a critical first step in nitrogen removal from estuarine and coastal environments. The first and rate limiting step in nitrification is catalyzed by the enzyme ammonia monooxygenase (AmoA). We evaluate the relationships between the abundance of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) amoA genes; potential nitrification rates; and environmental variables to identify factors influencing AOA abundance and nitrifier activity in estuarine sediments. Our results showed that potential nitrification rates increased as abundance of AOA amoA increased. In contrast, there was no relationship between potential nitrification rates and AOB amoA abundance. This suggests that AOA are significant in estuarine nitrogen cycling. Surprisingly, more of the variability in potential nitrification rates was predicted by salinity and pore water sulfide than by dissolved oxygen history.

Caffrey, J.M., Hollibaugh, J.T. and Mortazavi, B. 2016. Living oysters and their shells as sites of nitrification and denitrification. Marine Pollution Bulletin. (DOI: 10.1016/j.marpolbul.2016.08.038.)

Abstract
Oysters provide a critical habitat, are a food resource for higher trophic levels and support important commercial fisheries throughout the world. Oyster reefs can improve water quality by removing phytoplankton.While sediment denitrification may be enhanced adjacent to oyster reefs, little is known about nitrification and denitrification associated with living oysters and their shells. Wemeasured nitrification and denitrification in living oysters (Crassostrea virginica and Crassostrea gigas) and empty oyster shells. Nitrification was similar between live oysters and empty oyster shells, however, denitrification was enhanced significantly on living oysters compared to shells. This is the first demonstration of nitrification and denitrification associated with living oysters and their shells. Our data suggest that loss of historic oyster reefs has likely affected the resilience of estuaries to eutrophication. The additional benefit of oystermediated denitrification should be considered in restoration of oyster reefs as a tool for managing eutrophication.

Caffrey, J.M., Hollibaugh, J.T., Bano, N. and Haskins, J. 2010. Effects of upwelling on short term variability in microbial processes in estuarine sediments. Aquatic Microbial Ecology. 58:261-271. (DOI: 10.3354/ame01387)

Abstract
We examined short-term variability in sediment microbial processes and biogeochemistry in response to decreased irradiance accompanying an upwelling event. Potential nitrification, extractable nutrients, solid phase iron and pore water sulfide concentrations were measured several times at 3 locations in Elkhorn Slough, California, USA. Benthic fluxes of nitrate+nitrite, ammonium, phosphate, sediment oxygen consumption and denitrification from N2/Ar flux were also measured. Fog that was associated with upwelling in Monterey Bay reduced photosynthetically active radiation in Elkhorn Slough, which led to increased duration of water column hypoxia. Solid phase Fe3+ concentrations and potential nitrification rates declined while pore water sulfide increased over this period. While potential nitrification rates from this study are lower than rates from estuaries that do not experience hypoxia or anoxia, nitrifiers in Elkhorn Slough appear to be capable of adjusting to changing environmental conditions, specifically of tolerating low levels of sulfide. The nitrifying assemblage was similar to the community of ammonia-oxidizing bacteria and ammonia-oxidizing archaea that was previously reported from this system. Eutrophic shallow estuaries like Elkhorn Slough are delicately poised such that their sediment biogeochemistry responds quickly to relatively small changes in the light environment.

Cai, W.-J. 2003. Riverine inorganic carbon flux and rate of biological uptake in the Mississippi River plume. Geophysical Research Letters. 30(2):1032-1035.

Abstract
Inorganic carbon parameters were studied for the first time in the Mississippi River estuary and plume. Area-integrated biological uptake rates (1.5–3 gC m^-2 d^-1) derived from riverine total dissolved inorganic carbon (DIC) and total alkalinity (TAlk) fluxes as well as that based on the consumptions of DIC and TAlk in the plume are comparable to earlier results of 14C incubation in individual water samples. This rate is among the highest in the estuaries and plumes of the world’s largest rivers. Fluvial DIC flux (13.5 x 10^12 gC yr^-1) indicates a 16% increase in the inorganic carbon flux over the earlier estimate and perhaps an increase in the weathering rate in the Mississippi River basin over the past four decades.

Cai, W.-J. 2011. Estuarine and Coastal Ocean Carbon Paradox: CO2 Sinks or Sites of Terrestrial Carbon Incineration? Annual Review of Marine Science. 3:123-145. (DOI: 10.1146/annurev-marine-120709-142723)

Abstract
Estuaries are a major boundary in the land-ocean interaction zone where organic carbon (OC) and nutrients are being processed, resulting in a high water-to-air carbon dioxide (CO2) flux (0.25 Pg C y−1). The continental shelves, however, take up CO2 (0.25 Pg C y−1) from the atmosphere, accounting for approximately 17% of open ocean CO2 uptake (1.5 Pg C y−1). It is demonstrated here that CO2 release in estuaries is largely supported by microbial decomposition of highly productive intertidal marsh biomass. It appears that riverine OC, however, would bypass the estuarine zone, because of short river-transit times, and contribute to carbon cycling in the ocean margins and interiors. Low-latitude ocean margins release CO2 because they receive two-thirds of the terrestrial OC. Because of recent CO2 increase in the atmosphere, CO2 releases from low latitudes have become weaker and CO2 uptake by mid- and high-latitude shelves has become stronger, thus leading to more dissolved inorganic carbon export to the ocean.

Cai, W.-J. and Dai, M. 2004. Comment on "Enhanced open ocean storage of CO2 from shelf sea pumping". Science. 306:1477c.

Abstract
In a well-designed North Sea study, Thomas et al. found that atmospheric carbon dioxide (CO2) was absorbed by continental shelf water and was eventually exported into the North Atlantic Ocean. The work confirmed preliminary observations in the same area and provided support for the continental shelf pump hypothesis. Thomas et al. then extrapolated "the CO2 uptake by the North Sea to the global scale" and inferred a net oceanic uptake of atmospheric CO2 by coastal oceans of 0.4 Pg C year^–1. A previous global extrapolation based on limited observations in the East China Sea (ECS) suggested an even greater air-sea CO2 flux of 1.0 Pg C year^–1 in the world's continental shelf. We are concerned with such extrapolations of regional studies to the global scale without cautioning readers that no current consensus exists on this issue.

Cai, W.-J., Dai, M. and Wang, Y. 2006. Air-sea exchange of carbon dioxide in ocean margins: A province-based synthesis. Geophysical Research Letters. 33:L12603. (DOI: 10.1029/2006GL026219)

Abstract
In determining global sea-to-air CO2 flux from measurements or models, the ocean margin has not been resolved from the land or the open ocean. Recent studies have indicated that shelves can be either a large sink or a source for atmospheric CO2. This CO2 sink/source term may substantially alter our current view of the global carbon budget for land and oceans. However, past fieldwork and synthesis have focused on a few shelves in the northern temperate zone while the vast majority of other shelves are ignored. By dividing the highly heterogeneous shelves into seven provinces, we suggest that the continental shelves are a sink for atmospheric CO2 at mid-high latitudes (-0.33 Pg C a-1) and a source of CO2 at low latitudes (0.11 Pg C a-1). Warm temperature and high terrestrial organic carbon input are most likely responsible for the CO2 release in low latitude shelves.

Cai, W.-J., Dai, M., Wang, Y., Zhai, W., Chen, T.H.S., Zhang, F., Chen, Z. and Wang, Z. 2004. The biogeochemistry of inorganic carbon and nutrients in the Pearl River estuary and the adjacent Northern South China Sea. Continental Shelf Research. 24:1301-1319.

Abstract
The Zhu-jiang (Pearl River) estuary and its adjacent continental shelf in the Northern South China Sea (SCS) is unique in that its drainage basin is located entirely in a subtropical zone with heavy population development, and therefore represents an important regime for biogeochemical studies on how large rivers influence continental shelves. The near-zero salinity end member has high nutrient concentrations (silicate 130–140 uM, nitrate 75–100 uM and phosphate 0.2–1.2 uM) and relatively high total dissolved inorganic carbon (DIC) (1500 uM) and alkalinity (~1650 uM) values. Water column DIC, alkalinity, and nutrient in the estuary are largely controlled by mixing of waters from different tributaries with different drainage basin chemistry, anthropogenic influence, and degree of estuarine recycling. Biological uptake of nutrients and inorganic carbon occur in the outer estuary and inner shelf areas supported by riverine nutrients. The N/Pand Si/P ratios are generally very high within the estuary. The summertime area-integrated biological production rate of 0.8 gCm^-2 d^-1 is estimated based on the depletion of DIC and alkalinity relative to the conservative mixing line and a plume travel time. This estimate agrees reasonably well with 14C based primary production rates (PP) and with that from effective river phosphate flux. Biological production decreases about 10-fold in the open continental shelf and slope and is largely supported by mixing with subsurface water. A comparison of DIC, phosphate, and nitrate concentrations in the surface mixing layer and at the bottom of the euphotic zone with the 14C-based PP (0.13 gCm^-2 d^-1) suggests that the surface water residence time in the Northern SCS is B1.3 years. The N/P, Si/P, and Si/C ratios are 15, 25, and 0.15, respectively. The subtropical Pearl River study is also compared to other large rivers with regard to differences in both natural processes (i.e., weathering rates) and anthropogenic influences (i.e., nutrient input) between these different river–estuary systems.

Cai, W.-J., Hu, X., Huang, W.-J., Jiang, L., Wang, Y. and Peng, T.-H. 2010. Alkalinity distribution in the western North Atlantic Ocean margins. Journal of Geophysical Research. 115(C08014):15. (DOI: 10.1029/2009JC005482)

Abstract
Total alkalinity (TA) distribution and its relationship with salinity (S) along the western North Atlantic Ocean (wNAO) margins from the Labrador Sea to tropical areas are examined in this study. Based on the observed TA-S patterns, the mixing processes that control alkalinity distribution in these areas can be categorized into a spectrum of patterns that are bracketed by two extreme mixing types, i.e., alongshore current-dominated and river-dominated. Alongshore current-dominated mixing processes exhibit a segmented mixing line with a shared mid-salinity end-member. In such cases (i.e., Labrador Sea, Gulf of Maine, etc.), the y-intercept of the high salinity segment of the mixing line is generally higher than the local river alkalinity values, and it reflects the mixing history of the alongshore current. In contrast, in river-dominated mixing (Amazon River, Caribbean Sea, etc.), good linear relationships between alkalinity and salinity are generally observed, and the zero salinity intercepts of the TA-S regressions roughly match those of the regional river alkalinity values. TA-S mixing lines can be complicated by rapid changes in the river end-member value and by another river nearby with a different TA value (e.g., Mississippi-Atchafalaya/Gulf of Mexico). In the wNAO margins, regression intercepts and river end-members have a clear latitudinal distribution pattern, increasing from a low of ∼300 µmol kg^−1 in the Amazon River plume to a high value between ∼500–1100 µmol kg^−1 in the middle and high latitude margins. The highest value of ∼2400 µmol kg^−1 is observed in the Mississippi River influenced areas. In addition to mixing control, biological processes such as calcification and benthic alkalinity production may also affect ocean margin alkalinity distribution. Therefore, deriving inorganic carbon system information in coastal oceans using alkalinity-salinity relationships, in particular, those of generic nature, may lead to significant errors.

Cai, W.-J., Wang, Y., Krest, J. and Moore, W.S. 2003. The geochemistry of dissolved inorganic carbon in a surficial groundwater aquifer in North Inlet, South Carolina and the carbon fluxes to the coastal ocean. Geochimica et Cosmochimica Acta. 67(5):631-637.

Abstract
Abstract—We report measurements of pH, total dissolved inorganic carbon (DIC), total or titration alkalinity (TAlk), Ca2+, Mg2+, sulfate, and sulfide data at the seawater-freshwater interface in a shallow groundwater aquifer in North Inlet, South Carolina. These measurements and a diagenetic modeling analysis indicate that the groundwaters at North Inlet are mixtures of seawater and freshwater end-members and are seriously modified by carbon dioxide inputs from organic carbon degradation via SO42- reduction across the entire salinity range and fermentation and CaCO3 dissolution in the low-salinity region. DIC and TAlk are several times higher than the theoretical dilution line, whereas Ca2+ is slightly higher and SO4^2- is somewhat lower than the dilution line. Partial pressure of CO2 in the groundwater is extremely high (0.05 to 0.12 atm). These deviations are consistent with theoretical predictions from known diagenetic reactions. Estimated groundwater DIC fluxes to the South Atlantic Bight from either the surficial aquifer (via salt marshes) or the Upper Floridan Aquifer (direct input) are significant when compared to riverine flux in this area.

Cai, W.-J., Wang, Z. and Wang, Y. 2003. The role of marsh-dominated heterotrophic continental margins in transport of CO2 between the atmosphere, the land-sea interface and the ocean. Geophysical Research Letters. 30(16):1849.

Abstract
Recent air-to-sea CO2 flux measurements at several major continental shelves suggest that shelves may act as a one-way pump and absorb atmospheric CO2 into the ocean. The U.S. South Atlantic Bight (SAB) contrasts these findings in that it acts as a source of CO2 to the atmosphere while simultaneously exporting dissolved inorganic carbon (DIC) to the open ocean. The shelf-wide heterotrophy and carbon exports in the SAB are subsidized by the export of organic carbon from the abundant intertidal marshes, which are a sink for atmospheric CO2. It is proposed here that the SAB represents a marsh-dominated heterotrophic ocean margin as opposed to river-dominated autotrophic margins. Based on this and other studies, DIC export flux from margins to the open ocean must be significant in the overall global ocean carbon budget.

Cai, W.-J., Wiebe, W.J., Wang, Y. and Sheldon, J.E. 2000. Intertidal marsh as a source of dissolved inorganic carbon and a sink of nitrate in the Satilla River-estuarine complex in the southeastern U.S. Limnology & Oceanography. 45:1743-1752.

Abstract
Total dissolved inorganic carbon (DIC), total alkalinity (TA), pH, and nitrate + nitrite (NOx) data collected during the summer of 1996 in the Satilla River estuary in the southeastern U.S. were used to assess fluxes of DIC and NOx between intertidal marshes and estuarine waters and to model system NOx dynamics. Nitrate and nitrite are produced in the low-salinity portion of the estuary. The intertidal marshes are sites of intensive respiration that export DIC to the estuary and remove NOx. An integrated view is presented on the nitrification and denitrification processes in the marsh/estuarine complex and their relationship to CO2 generation rates. The distribution of NOx in the marsh and estuarine waters indicates that all NOx generated in the marsh–estuary system is removed in the intertidal marshes, most likely via denitrification. Model analysis of NOx and river flow data for three seasons indicates that NOx distribution in the estuarine water is also determined by river flow rates. Export fluxes of NOx to the coastal ocean are insignificant in all seasons when compared to NOx production rates in the entire system; however, they are significantly higher than NOx inputs from the river end member in October 1996. Although only a small fraction (~10%) of DIC generated in the marshes is exported to the coastal sea and around 90% is lost to the atmosphere, it represents a nearly threefold increase in riverine DIC flux to the ocean.

Callaway, R.M., Pennings, S.C. and Richards, C.L. 2003. Phenotypic plasticity and interactions among plants. Ecology. 84(5):1115-1128.

Abstract
We know a great deal about the plastic responses of plant phenotypes to the abiotic and biotic environment, but very little about the consequences of phenotypic plasticity for plant communities. In other words, we know that plant traits can vary widely for a given genotype, but we know little about the importance of trait-mediated interactions (TMI) among plants. Here, we discuss three major factors that affect the expression of phenotypic plasticity: variation in the abiotic environment, variation in the presence or identity of neighbors, and variation in herbivory. We consider how plastic responses to these factors might affect interactions among plants. Plastic responses to the abiotic environment have important consequences for conditionality in competitive effects, to the point of causing shifts from competitive to facilitative interactions. Because plants show a high degree of plasticity in response to neighbors, and even to the specific identify of neighbors, phenotypic plasticity may allow species to adjust to the composition of their communities, promoting coexistence and community diversity. Likewise, plastic responses to consumers may have various and counterintuitive consequences: induction of plant resistance, compensatory growth, and increased resource uptake may affect interactions among plants in ways that cannot be predicted simply by considering biomass lost to consumers. What little we know about TMI among plants suggests that they should not be ignored in plant community theory. Although work to date on the community consequences of phenotypic plasticity has been hampered by experimental constraints, new approaches such as manipulating phenotypes by using signals instead of actual environmental conditions and the use of transgenic plants should allow us to rapidly expand our understanding of the community consequences of plant plasticity.

Campbell, J.L., Rustad, L.E., Porter, J.H., Taylor, J.R., Dereszynkski, E.W., Shanley, J.B., Gries, C., Henshaw, D.L., Martin, M.E., Sheldon, W.M. Jr. and Boose, E.R. 2013. Quantity is Nothing without Quality: Automated QA/QC for Streaming Environmental Sensor Data. BioScience. 63(7):574-585. (DOI: 10.1525/bio.2013.63.7.10)

Abstract
Sensor networks are revolutionizing environmental monitoring by producing massive quantities of data that are being made publicly available in near-real-time. These new data streams pose a challenge for ecologists because traditional approaches to quality assurance and quality control are no longer practical when confronted with extremely large data sets. Automated methods for rapidly identifying and (ideally) correcting problematic data are necessary for handling the volume of data generated by streaming sensor networks. Advances in sensor hardware have outpaced software, creating a need for tools to implement automated quality assurance and quality control procedures, produce graphical and statistical summaries for review, and track the provenance of the data. Use of automated tools would enhance data integrity and reliability, and reduce delays in releasing data products. Development of community-wide standards for quality assurance and quality control can instill confidence in sensor data and improve interoperability across environmental sensor networks.

Cao, F., Mishra, D., Schalles, J.F. and Miller, W. 2018. Evaluating ultraviolet (UV) based photochemistry in optically complex coastal waters using the Hyperspectral Imager for the Coastal Ocean (HICO). Estuarine, Coastal and Shelf Science. 215. (DOI: 10.1016/j.ecss.2018.10.013)

Abstract
Knowledge of light partitioning into different optically active constituents, particularly chromophoric dissolved organic matter (CDOM) in the ultraviolet (UV) is indispensable for understanding UV dependent biogeochemical issues including photochemical processes in optically complex waters. Herein a new approach is presented to investigate photochemistry by blending two ocean color algorithms, namely the composite SeaUV (Cao et al., 2014) and the SeaCDOM (Cao and Miller, 2014) algorithms, and applying them to visible remote sensing reflectance (Rrs) measured using the Hyperspectral Imager for the Coastal Ocean (HICO). As illustrated using photochemical carbon monoxide (CO) production from CDOM, this model approach allows high resolution examination of UV optical details with estimates of both depth specific and depth-integrated photoproduction rates in a dynamic estuarine/coastal environment. Decoupled retrievals of inherent and apparent optical properties (i.e. diffuse attenuation coefficient (Kd) and CDOM absorption coefficient (ag)) using two distinct ocean color algorithms over the entire UV spectrum allow a synoptically dynamic view of CDOM’s contribution to light attenuation (ag/Kd). This provides new potential to probe UV processes in complex coastal waters on regional as well as global scales using remote sensing of ocean color.

Chalifour, B., Hoogveld, J., Derksen-Hooijberg, M., Harris, K., Uruena, J., Sawyer, W., van der Heide, T. and Angelini, C. 2019. Drought alters the spatial distribution, grazing patterns, and radula morphology of a fungal-farming salt marsh snail. Marine Ecology Progress Series. 620:1-13. (DOI: 10.3354/meps12976)

Abstract
Climate change is altering consumer−plant interactions in ecosystems worldwide. How consumers alter their spatial distribution, grazing activities, and functional morphology in response to climate stress can determine whether their effects on plants intensify or relax. Few studies have considered multiple consumer response metrics to elucidate the mechanisms underpinning the resulting changes in consumer−plant interactions. Here, we tested how drought stress influences the interaction between the dominant consumer, the fungal-farming periwinkle snail Littoraria irrorata, and a foundational plant, cordgrass Spartina alterniflora, in a southeastern US salt marsh. In a 4 mo field experiment, we maintained moderate snail densities in mesh control chambers and clear plastic climate chambers that simulated drought by elevating temperatures and drying soils. Monitoring revealed that snails more often congregated on cordgrass stems than leaves in climate chambers than in controls. Image analyses indicated that this behavioral shift corresponded to snails inflicting shorter, but more numerous, fungal-infested scars on cordgrass leaves, and causing less plant damage in climate chambers than controls. Coincident with their net reduction in grazing, snails maintained longer radulae, whose central teeth were blunter and lateral teeth were sharper, in climate chambers compared to controls. These results suggest that under drought, snail radulae may experience less frictional wear and that, at inter mediate densities, snail− cordgrass interactions re lax. Together with prior research showing that at high densities, snails can denude cordgrass during drought, we conclude that consumer density, behavior, and morphological responses must be integrated in predictions of how climate change will affect the direction, strength, and stability of consumer− plant interactions.

Cheong, S.M., Silliman, B.R., Wong, P., Wesienback, B., Kim, C. and Guannel, G. 2013. Coastal Adaptation Defense with Ecological Engineering. Nature Climate Change. 3:787 - 791. (DOI: 10.1038/NCLIMATE1854)

Abstract
The use of combined approaches to coastal adaptation in lieu of a single strategy, such as sea-wall construction, allows for better preparation for a highly uncertain and dynamic coastal environment. Although general principles such as mainstreaming and no- or low-regret options exist to guide coastal adaptation and provide the framework in which combined approaches operate, few have examined the interactions, synergistic effects and benefits of combined approaches to adaptation. This Perspective provides three examples of ecological engineering — marshes, mangroves and oyster reefs — and illustrates how the combination of ecology and engineering works.

Clark, C.M., Cleland, E.E., Collins, S.L., Fargione, J.E., Gough, L., Gross, K.L., Pennings, S.C., Suding, K.N. and Grace, J.B. 2007. Environmental and plant community determinants of species loss following nitrogen enrichment. Ecology Letters. 10:596-607.

Abstract
Global energy use and food production have increased nitrogen inputs to ecosystems worldwide, impacting plant community diversity, composition, and function. Previous studies show considerable variation across terrestrial herbaceous ecosystems in the magnitude of species loss following nitrogen (N) enrichment. What controls this variation remains unknown. We present results from 23 N-addition experiments across North America, representing a range of climatic, soil and plant community properties, to determine conditions that lead to greater diversity decline. Species loss in these communities ranged from 0 to 65% of control richness. Using hierarchical structural equation modelling, we found greater species loss in communities with a lower soil cation exchange capacity, colder regional temperature, and larger production increase following N addition, independent of initial species richness, plant productivity, and the relative abundance of most plant functional groups. Our results indicate sensitivity to N addition is co-determined by environmental conditions and production responsiveness, which overwhelm the effects of initial community structure and composition.

Cleland, E.E., Clark, C.M., Collins, S.L., Fargione, J.E., Gough, L., Gross, K.L., Milchunas, D.G., Pennings, S.C., Bowman, W.D., Burke, I.C., Lauenroth, G.P., Robertson, J.C., Simpson, J.C., Tilman, D. and Suding, K.N. 2008. Species responses to nitrogen fertilization in herbaceous plant communities, and associated species traits. Ecology. 89:1175.

Abstract
This synthetic dataset contains plant species relative abundance measures from 35 nitrogen (N) fertilization experiments conducted at 10 sites across North America. The dataset encompasses the fertilization responses of 691 species from 1,159 experimental plots. The methodology varied among experiments, in particular with regards to the type and amount of N added, plot size, species composition measure (biomass harvest, pin count or percent cover), additional experimental manipulations, and experimental duration. At each site, each species has been classified according to a number of easily identified categorical functional traits, including life history, life form, the number of cotyledons, height relative to the canopy, potential for clonal growth, and nativity to the United States. Additional data are available for many sites, indicated by references to publications and websites. Analyses of these data have shown that N enrichment significantly alters community composition in ways that are predictable on the basis of plant functional traits as well as environmental context. This dataset could be used to answer a variety of questions about how plant community composition and structure respond to environmental changes.

Cleland, E.E., Clark, C.M., Collins, S.L., Fargione, J.E., Gough, L., Gross, K.L., Pennings, S.C. and Suding, K.N. 2011. Patterns of trait convergence and divergence among native and exotic species in herbaceous plant communities are not modified by nitrogen enrichment. Journal of Ecology. 99:1327-1338. (DOI: 10.1111/j.1365-2745.2011.01860.x)

Abstract
1. Community assembly theories predict that the success of invading species into a new community should be predictable by functional traits. Environmental filters could constrain the number of successful ecological strategies in a habitat, resulting in similar suites of traits between native and successfully invading species (convergence). Conversely, concepts of limiting similarity and competitive exclusion predict native species will prevent invasion by functionally similar exotic species, resulting in trait divergence between the two species pools. Nutrient availability may further alter the strength of convergent or divergent forces in community assembly, by relaxing environmental constraints and/or influencing competitive interactions.2. To investigate how nutrient availability influences forces of divergence and convergence during the invasion of exotic species into native communities, we conducted multivariate analyses of community composition and functional traits from naturally assembled plant communities in long-term nitrogen (N) addition experiments across North America.3. Relative abundances of key functional traits differed between the native and exotic plant communities, consistent with limiting similarity or a trait bias in the exotic species pool. Environmental context also played an important role in invasion because sites varied in the identity of the traits that predicted dissimilarity between native and exotic communities. Nitrogen enrichment did not alter these patterns.4. Nitrogen enrichment tended to increase exotic abundance, but this result was driven by a dramatic increase in exotics in only a few experiments. When similarity between native and exotic communities was included in the statistical model, N enrichment no longer predicted an increase in exotic relative abundance. Instead, sites with the highest abundance of exotic species were the ones where native and exotic communities had the highest trait similarity.5. Synthesis. Our analysis of natural patterns of invasion across herbaceous communities in North America found evidence of both divergent and convergent forces on community assembly with exotic species. Together, these results suggest that while functionally dissimilar exotic species may be more likely to invade, they are unlikely to become abundant unless they have traits pre-adapting them to environmental conditions in their invaded range. Contrary to prior studies, invasion was not consistently promoted by N enrichment.

Collins, S.L., Suding, K.N., Cleland, E.E., Batty, M., Pennings, S.C., Gross, K.L., Grace, J.B., Gough, L., Fargione, J.E. and Clark, C.M. 2008. Rank clocks and plant community dynamics. Ecology. 89(12):3534-3541. (DOI: 10.1890/07-1646.1)

Abstract
Summarizing complex temporal dynamics in communities is difficult to achieve in a way that yields an intuitive picture of change. Rank clocks and rank abundance statistics provide a graphical and analytical framework for displaying and quantifying community dynamics. We used rank clocks, in which the rank order abundance for each species is plotted over time in temporal clockwise direction, to display temporal changes in species abundances and richness. We used mean rank shift and proportional species persistence to quantify changes in community structure in long-term data sets from fertilized and control plots in a late successional old field, frequently and infrequently burned tallgrass prairie, and Chihuahuan desert grassland and shrubland communities. Rank clocks showed that relatively constant species richness masks considerable temporal dynamics in relative species abundances. In the old field, fertilized plots initially experienced high mean rank shifts that stabilized rapidly below that of unfertilized plots. Rank shifts were higher in infrequently burned vs. annually burned tallgrass prairie and in desert grassland compared to shrubland vegetation. Proportional persistence showed that arid grasslands were more dynamic than mesic grasslands. We conclude that rank clocks and rank abundance statistics provide important insights into community dynamics that are often hidden by traditional univariate approaches.

Craft, C.B. 2001. Soil organic carbon, nitrogen and phosphorus as indicators of recovery in restored Spartina marshes. Ecological Restoration. 19:87-91.

Abstract
Scientists frequently measure soil properties, such as organic matter, nutrient content and particle size (sand, silt, clay), to gauge the development of functional equivalence in terrestrial and wetland restoration projects (Dancer and others, 1977; Marrs and others, 1981, Craft and others, 1988, 1999; Langis and others, 1991; Li and Daniels, 1994, Daniels and Zipper, 1995; Bishel-Machung and others, 1996; Piehler and others, 1998). Organic matter and nitrogen content are especially useful because they serve as indicators of energy flow (carbon) and nutrient (nitrogen) cycles. Because many ecosystems are nitrogen limited, ecosystem development during primary succession or succession on created, restored, or rehabilitated sites depends on accumulation of nitrogen in the soil and plant biomass (Marrs and others, 1981). In detritus-based ecosystems, such as forests and wetlands, soil organic matter supports secondary production by contributing detritus to hetertrophic organisms (Craft and others, 1999) and labile carbon (C) to fuel microbial processes like denitrification (Thompson and others, 1995) and nitrogen (N) fixation (Piehler and others, 1998).

Craft, C.B. 2007. Freshwater input structures soil properties, vertical accretion, and nutrient accumulation of Georgia and U.S. tidal marshes. Limnology & Oceanography. 52(3):1220-1230.

Abstract
To identify relationships between freshwater input and marsh soil properties, measurements of bulk density, nutrients (carbon [C], nitrogen [N], phosphorus [P]), accretion, and accumulation were compared in tidal marshes of three estuaries of Georgia that varied in delivery of freshwater. Soil organic C and N (0-30 cm) were two times greater in marshes of the freshwater-dominated Altamaha River than in the salt marshes of Doboy Sound and Sapelo River. 137Cs accretion and accumulation of organic C and N were three to five times greater in freshwater-dominated marshes than in salt marshes. The patterns observed in Georgia marshes were geographically general; data for tidal freshwater and brackish marsh soils compiled from 61 studies in the conterminous United States showed lower bulk density and higher percent organic C and N than salt marshes, regardless of geographic region. Salinity, a proxy for freshwater input, was inversely correlated with percent soil organic C and N and with vertical accretion in Georgia marshes and in marshes elsewhere in the conterminous United States. There was no relationship between above- or belowground emergent plant production and salinity of Georgia marshes but the rate of root decomposition was positively related to salinity, and decomposition rate was negatively related to percent soil organic C and C accumulation. In Georgia tidal marshes and elsewhere, soil organic matter content and accumulation are mediated by freshwater through its effects on decomposition.

Craft, C.B. 2012. Tidal freshwater forest accretion does not keep pace with sea level rise. Global Change Biology. 18:3615-3623. (DOI: 10.1111/gcb.12009)

Abstract
Soil properties, accretion, and accumulation were measured in tidal freshwater forests (tidal forests) of the Ogeechee, Altamaha, and Satilla rivers of the South Atlantic (Georgia USA) coast to characterize carbon (C) sequestration and nutrient (nitrogen-N, phosphorus-P) accumulation in these understudied, uncommon, and ecologically sensitive wetlands. Carbon sequestration and N and P accumulation also were measured in a tidal forest (South Newport River) that experiences saltwater intrusion to evaluate the effects of sea level rise (SLR) and saltwater intrusion on C, N and P accumulation. Finally, soil accretion and accumulation of tidal forests were compared with tidal fresh, brackish and salt marsh vegetation downstream to gauge how tidal forests may respond to SLR. Soil accretion determined using 137C and 210Pb averaged 1.3 and 2.2 mm yr−1, respectively, and was substantially lower than the recent rate of SLR along the Georgia coast (3.0 mm yr−1). Healthy tidal forest soils sequestered C (49–82 g m−2 yr−1), accumulated N (3.2–5.3 g m−2 yr−1) and P (0.29–0.56 g m−2 yr−1) and trapped mineral sediment (340–650 g m−2 yr−1). There was no difference in long-term accretion, C sequestration, and nutrient accumulation between healthy tidal forests and tidal forests of the South Newport River that experience saltwater intrusion. Accelerated SLR is likely to lead to decline of tidal forests and expansion of oligohaline and brackish marshes where soil accretion exceeds the current rate of SLR. Conversion of tidal forest to marshes will lead to an increase in the delivery of some ecosystem services such as C sequestration and sediment trapping, but at the expense of other services (e.g. denitrification, migratory songbird habitat). As sea level rises in response to global warming, tidal forests and their delivery of ecosystem services face a tenuous future unless they can migrate upriver, and that is unlikely in most areas because of topographic constraints and increasing urbanization of the coastal zone.

Craft, C.B., Clough, J., Ehman, J., Joye, S.B., Park, R., Pennings, S.C., Guo, H. and Machmuller, M. 2009. Forecasting the effects of accelerated sea level rise on tidal marsh ecosystem services. Frontiers in Ecology and the Environment. 7(2):73-78. (DOI: 10.1890/070219)

Abstract
We used field and laboratory measurements, geographic information systems, and simulation modeling to investigate the potential effects of accelerated sea-level rise on tidal marsh area and delivery of ecosystem services along the Georgia coast. Model simulations using the Intergovernmental Panel on Climate Change (IPCC) mean and maximum estimates of sea-level rise for the year 2100 suggest that salt marshes will decline in area by 20% and 45%, respectively. The area of tidal freshwater marshes will increase by 2% under the IPCC mean scenario, but will decline by 39% under the maximum scenario. Delivery of ecosystem services associated with productivity (macrophyte biomass) and waste treatment (nitrogen accumulation in soil, potential denitrification) will also decline. Our findings suggest that tidal marshes at the lower and upper salinity ranges, and their attendant delivery of ecosystem services, will be most affected by accelerated sealevel rise, unless geomorphic conditions (ie gradual increase in elevation) enable tidal freshwater marshes to migrate inland, or vertical accretion of salt marshes to increase, to compensate for accelerated sea-level rise.

Craft, C.B., Clough, J., Ehman, J., Joye, S.B., Park, R., Pennings, S.C., Guo, H. and Machmuller, M. 2009. SLR and ecosystem services: a response to Kirwan and Guntenspergen. Frontiers in Ecology and the Environment. 7:127-128.

Abstract
We respond to four points made by Kirwan and Guntenspergen (K&G). First, K&G mention that uncertainties exist with model inputs in regard to the accuracy of source data and their reference to different datums, which are mathematical surfaces on which mapping and coordinate systems are based. The “sea level affects marshes model” (SLAMM) used elevation data based on light detection and ranging (LIDAR), where available, or more commonly the National Elevation Dataset (NED). Prior to input, the NED, wetland cover, and tidal data were all standardized to the same horizontal and vertical datums. K&G cite the 2.44-m root mean square error estimate for the NED that, although applicable to the entire dataset, underestimates accuracy within our study region for two reasons: (1) throughout our study region, the NED was produced from 1:24000-scale hypsography, using the two methods with the highest accuracy (Gesch 2007), thereby reducing errors relative to the entire NED; (2) the 5-ft (~1.5-m) contour intervals in our study domain are smaller than the 10-ft (~3-m) intervals typical in inland areas, again reducing errors relative to the NED as a whole. Nevertheless, K&G are correct that SLAMM did not incorporate error estimates into this analysis. We recognize that the ability to perform uncertainty analysis is a desirable model feature and plan to implement it for future publications. Producing detailed maps for local planning purposes, however, was not the goal of our paper.

Craft, C.B., Herbert, E., Li, F., Smith, D., Schubauer-Berigan, J.P., Widney, S., Angelini, C., Pennings, S.C., Medeiros, P.M., Byers, J. and Alber, M. 2016. Climate change and the fate of coastal wetlands. Wetland Science and Practice. 33(3):70-73.

Abstract
Coastal wetlands, including tidal marshes and forests, provide a number of key ecosystem services, including habitat for recreationally and commercially important finfish and shellfish, protection from wind, waves, storms and floods, and removal of excess nutrients, namely nitrogen (N) and phosphorus (P), from agricultural and urban runoff (e.g., Tiner 2013). Along the coast, climate change will be manifested as rising sea level with attendant coastal flooding and saltwater intrusion. A more immediate impact which has already been experienced is drought, particularly in late summer and fall. These processes will lead to migration of tidal wetlands inland, where possible, and changes in habitat as freshwater wetlands convert to brackish marsh or open water. As part of the National Science Foundation’s Georgia Coastal Ecosystems Long Term Ecological Research (GCE LTER) project, scientists from seven institutions of higher learning, including the University of Georgia, Indiana University, Virginia Institute of Marine Sciences, University of Houston, University of Florida, Georgia Southern University, College of Coastal Georgia, and the U.S. Environmental Protection Agency, initiated a field experiment - Seawater Addition Long Term Experiment or SALTEx - to investigate how saltwater intrusion and increased flooding will alter the direction and pace of change of microbial, plant, and animal communities and key biogeochemical processes in a tidal freshwater marsh. SALTEx consists of an array of field plots that are used to answer three main questions regarding sea level rise and saltwater intrusion: 1. How does long-term, chronic (“press”) addition of diluted seawater affect tidal freshwater marsh structure and function? 2. What are the effects of periodic pulsing of diluted seawater to simulate low river flow or drought conditions? 3. What are the effects of freshwater additions?

Crotty, S.M., Ortals, C., Pettengill, T.M., Shi, L., Olabarrieta, M., Joyce, M.A., Altieri, A.H., Morrison, E., Bianchi, T.S., Craft, C.B., Bertness, M.D. and Angelini, C. 2020. Sea-level rise and the emergence of a keystone grazer alter the geomorphic evolution and ecology of southeast US salt marshes. PNAS. (DOI: https://doi.org/10.1073/pnas.1917869117)

Abstract
Keystone species have large ecological effects relative to their abundance and have been identified in many ecosystems. However, global change is pervasively altering environmental conditions, potentially elevating new species to keystone roles. Here, we reveal that a historically innocuous grazer—the marsh crab Sesarma reticulatum—is rapidly reshaping the geomorphic evolution and ecological organization of southeastern US salt marshes now burdened by rising sea levels. Our analyses indicate that sea-level rise in recent decades has widely outpaced marsh vertical accretion, increasing tidal submergence of marsh surfaces, particularly where creeks exhibit morphologies that are unable to efficiently drain adjacent marsh platforms. In these increasingly submerged areas, cordgrass decreases belowground root:rhizome ratios, causing substrate hardness to decrease to within the optimal range for Sesarma burrowing. Together, these bio-physical changes provoke Sesarma to aggregate in high-density grazing and burrowing fronts at the heads of tidal creeks (hereafter, creekheads). Aerial-image analyses reveal that resulting “Sesarma-grazed” creekheads increased in prevalence from 10 ± 2% to 29 ± 5% over the past <25 y and, by tripling creek-incision rates relative to nongrazed creekheads, have increased marsh-landscape drainage density by 8 to 35% across the region. Field experiments further demonstrate that Sesarma-grazed creekheads, through their removal of vegetation that otherwise obstructs predator access, enhance the vulnerability of macrobenthic invertebrates to predation and strongly reduce secondary production across adjacent marsh platforms. Thus, sea-level rise is creating conditions within which Sesarma functions as a keystone species that is driving dynamic, landscape-scale changes in salt-marsh geomorphic evolution, spatial organization, and species interactions.

Daleo, P., Silliman, B.R., Alberti, J., Escapa, M., Canepuccia, A., Pena, N. and Iribarne, O. 2009. Grazer facilitation of fungal infection and the control of plant growth in south-western Atlantic salt marshes. Journal of Plant Ecology. 97:781-787. (DOI: 10.1111/j.1365-2745.2009.01508.x)

Abstract
While great effort has been made in documenting the processes that drive plant-induced susceptibility after herbivore attack and it is widely accepted that herbivores can facilitate plant diseases, the relative importance of this interaction in controlling plant growth in natural systems remains largely unexplored.2. In south-western Atlantic salt marshes, we investigated the importance of disease after herbivory by examining: (i) whether or not a herbivorous crab facilitates disease (i.e. fungus infection) in marsh plants (Spartina alterniflora and S. densiflora) when clipping off small portions of leaves and (ii) the separate and interactive effects of crab grazing but fungal infection in controlling marsh plant growth.3.Our results show that crab grazing facilitates fungal infection in Spartina leaves. A factorial field experiment shows that both direct crab herbivory and fungal infection strongly suppress plant production (by more than 50%).4.Synthesis. These experimental results demonstrate that fungal infection following herbivory attack can decrease salt marsh plant production and that increased disease susceptibility can be a fundamental factor in controlling plant production in natural ecosystems, even in cases where herbivores do not directly inoculate the pathogen but only damage plant tissue.

Damashek, J., Tolar, B., Liu, Q., Okotie-Oyekan, A., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2018. Microbial oxidation of nitrogen supplied as selected organic nitrogen compounds in the South Atlantic Bight. Limnology and Oceanography. In press. (DOI: 10.1002/lno.11089)

Abstract
Dissolved organic nitrogen (DON) can account for a large fraction of the dissolved nitrogen (N) pool in the ocean, but the cycling of marine DON is poorly understood. Recent discoveries that urea- and cyanate-N can be oxidized by some strains of Thaumarchaeota suggest that these abundant microbes may be able to access and oxidize a fraction of the DON pool. However, measurements of the oxidation of N supplied as DON compounds are scarce. Here, we compare oxidation rates of N supplied as a variety of DON compounds in samples from Georgia coastal waters, where nitrifier communities are numerically dominated by Thaumarchaeota. Our data indicate that polyamine-N is particularly amenable to oxidation compared to the other DON compounds tested. Oxidation of N supplied as putrescine (1,4-diaminobutane) was generally higher than that of N supplied as glutamate, arginine, or urea, and was consistently 5–10% of the ammonia oxidation rate. Our data also suggest that the oxidation rate of polyamine-N may increase as the length of the carbon skeleton increases. Oxidation of N supplied as putrescine, urea, and glutamate were all highest near the coast and lower further offshore, consistent with patterns of ammonia oxidation in these waters. Though it is unclear whether oxidation of polyamine-N reflects direct oxidation by Thaumarchaeota or combines remineralization and subsequent ammonia oxidation, more rapid oxidation of N from putrescine compared to amino acids or urea suggests that polyamine-N may contribute significantly to nitrification in the ocean.

Davidson, A., Griffin, J., Atkins, R., Angelini, C., Coleman, F. and Silliman, B.R. 2015. Non-consumptive predator effects intensify grazer-plant interactions by driving vertical habitat shifts. Marine Ecology Progress Series. 537:49-58. (DOI: 10.3354/meps11419)

Abstract
Predators non-consumptively induce prey habitat shifts, driving trait-mediated indirect interactions (TMIIs) with basal resources. Whether prey seek refuge within or avoid predator-containing patches determines the spatial re-distribution of prey and influences the nature of resulting TMIIs. In a southeastern US salt marsh we tested how two species of sit-and-wait benthic predatory crab non-consumptively affect the habitat choices of grazing snails and how the resultant behavior affects cordgrass health. We first observed that snails climb higher on cordgrass around naturally-occurring crab burrows and that this habitat shift corresponds with increased cordgrass leaf damage, suggesting a localized TMII. Then, by adding caged crabs to artificial burrows in the field, we found causative evidence that either crab species could drive snails upwards to the cordgrass canopy, thereby increasing leaf damage within a ~12 cm radius, but found no evidence that experimentally added crabs induce horizontal dispersal of snails. Next, in a marsh undergoing die-off, we added caged crabs to remnant cordgrass patches being rapidly colonized by snails. Crabs did not affect the rate of snail colonization of remnant patches, but did drive snails upwards once they had colonized a patch, suggesting snails do not preferentially avoid - but alter how they locally utilize - patches of cordgrass in marsh die-off contexts. Our documentation of the spatial-scale and dimensionality of TMIIs in the field paves the way for spatially- explicit models of this interaction. More generally, our results suggest that TMIIs may be consistent, predictable and tractable, lending themselves to incorporation into food-web models.

Derksen-Hooijberg, M., Angelini, C., Hoogveld, J., Lamers, L., Borst, A., Smolders, A.J.P., Harpenslager, S.F., Govers, L.L. and van der Heide, T. 2019. Repetitive desiccation events weaken a salt marsh mutualism. Journal of Ecology. 107(5):2415-2426. (DOI: 10.1111/1365-2745.13178)

Abstract
Salt marshes suffered large‐scale degradation in recent decades. Extreme events such as hot and dry spells contributed significantly to this, and are predicted to increase not only in intensity, but also in frequency under future climate scenarios. Such repetitive extreme events may generate cumulative effects on ecosystem resilience. It is therefore important to elucidate how marsh vegetation responds to repetitive stress, and whether changes in key species interactions can modulate vegetation resilience.In this study, we investigated how moderate but repetitive desiccation events, caused by the combined effects of drought and high temperatures, affect cordgrass (Spartina alterniflora), the dominant habitat‐forming grass in southeastern US salt marshes. In a 4‐month field experiment, we simulated four consecutive desiccation events by periodically excluding tidal flooding and rainfall, while raising temperature. We crossed this desiccation treatment with the presence/absence of ribbed mussels (Geukensia demissa) – a mutualist of cordgrass known to enhance its desiccation resilience – and with grazing pressure by the marsh periwinkle (Littoraria irrorata) that is known to suppress cordgrass’ desiccation resilience.We found that each subsequent desiccation event deteriorated sediment porewater conditions, resulting in high salinity (53 ppt), low pH‐levels (3.7) and increased porewater Al and Fe concentrations (≈800 µmol/L and ≈1,500 µmol/L) upon rewetting. No effects on porewater chemistry were found as a result of snail grazing, while ribbed mussels strongly mitigated desiccation effects almost to control levels and increased cordgrass biomass by approximately 128%. Importantly, although cordgrass generally appeared healthy above‐ground at the end of the experiment, we found clear negative responses of the repetitive desiccation treatment on cordgrass below‐ground biomass, on proline (osmolyte) levels in shoots and on the number of tillers (−40%), regardless of mussel and/or snail presence.Synthesis. Even though the mutualism with mussels strongly mitigated chemical effects in the sediment porewater throughout the experiment, mussels could not buffer the adverse ecophysiological effects observed in cordgrass tissue. Our results therefore suggest that although mussels may alleviate desiccation stress, the predicted increased frequency and intensity of hot dry spells may eventually affect saltmarsh resilience by stressing the mutualism beyond its buffering capacity.

Derksen-Hooijberg, M., Angelini, C., Lamers, L., Borst, A., Smolders, A.J.P., Hoogveld, J., de Paoli, H., Silliman, B.R. and van der Heide, T. 2017. Mutualistic interactions amplify saltmarsh restoration success. Journal of Applied Ecology. 2017:1-10. (DOI: 10.1111/1365-2664.12960)

Abstract
1. Mounting evidence shows that the functioning and stability of coastal ecosystemsoften depends critically on habitat-forming foundation species such as seagrasses, mangroves and saltmarsh grasses that engage in facultative mutualistic interactions. However, although restoration science is now gradually expanding its longstanding paradigm of minimizing competition to including intraspecific, or within species, facilitation in its designs, the potential of harnessing mutualistic interactions between species for restoration purposes remains uninvestigated.2. Here, we experimentally tested whether a previously documented mutualism between marsh-forming Spartina alterniflora (cordgrass) and Geukensia demissa (mussels) can increase restoration success in degraded US saltmarshes.3. We found that co-transplanted mussels locally increased nutrients and reduced sulphide stress, thereby increasing cordgrass growth and clonal expansion by 50%. We then removed above-ground vegetation and mussels to simulate a disturbance event and discovered that cordgrass co-transplanted with mussels experienced three times greater survival than control transplants.4. Synthesis and applications. Our findings indicate that mussels amplify cordgrass recolonization and resilience over spatial and temporal scales that exceed those of their actual mutualistic interaction. By experimentally demonstrating that mutualistic partners can enable foundation species to overcome stress barriers to establish and persist, we highlight that coastal restoration needs to evolve beyond the sole inclusion of intraspecific-positive interactions. In particular, we suggest that integrating mutualisms in restoration designs may powerfully enhance long-term restoration success and ecosystem resilience in the many coastal ecosystems where mutualisms involving foundation species are important ecosystem-structuring interactions.

Di Iorio, D. and Castelao, R. 2013. The Dynamical Response of Salinity to Freshwater Discharge and Wind Forcing in Adjacent Estuaries on the Georgia Coast. Special Issue: Coastal Long Term Ecological Research. Oceanography. 26(3):44–51. (DOI: 10.5670/oceanog.2013.44)

Abstract
Ten years of oceanic and meteorological monitoring data were collected in order to understand the spatial and temporal patterns of salinity distribution across three adjacent estuaries in the Georgia Coastal Ecosystems Long Term Ecological Research domain. Empirical orthogonal function analysis shows that 95% of the subtidal salinity variability can be explained by two principle modes. The first mode is dominated by river discharge, and causes system-wide freshening throughout the domain. The second mode, which explains 8% of the variability, is correlated with subtidal sea surface height and, hence, alongshore winds. The response in Sapelo and Doboy Sounds to this second mode, however, is out of phase with that of Altamaha Sound. During upwelling-favorable winds when coastal sea surface height decreases, Altamaha Sound freshens, and salinity increases in Doboy and Sapelo Sounds. On the other hand, freshening in Doboy and Sapelo Sounds and a salinity increase in Altamaha Sound accompany downwelling-favorable winds. A regional ocean model of a highly idealized coastal domain of three adjacent estuaries connected by the Intracoastal Waterway is consistent with the observations—river discharge and upwelling-favorable winds freshen the coastal domain so that when downwelling-favorable winds occur, the coastal freshwater originating in the Altamaha River is transported into Sapelo and Doboy Sounds. Model results suggest that the Intracoastal Waterway and the complex network of channels that connects the sounds play a dominant role in water exchange between the adjacent estuaries.

Di Iorio, D. and Kang, K. 2007. Variations of turbulent flow with river discharge in the Altamaha River Estuary, Georgia. Journal of Geophysical Research - Oceans. 112:C05016. (DOI: 10.1029/2006JC003763)

Abstract
Turbulent flow characteristics under two significantly different river discharge periods were studied in the Altamaha River Estuary, GA using a variety of moored instrumentation, combined with detailed water column profiling from an anchored vessel. Estimates of the Reynolds stress, shear production (P), and dissipation rate (epsilon) were derived and compared for the two contrasting river conditions which essentially characterized the estuary as weakly stratified during low discharge (2001) and partially mixed during high discharge (2003). Wave effects were removed from the measurement of turbulent kinetic energy (TKE) using a linear filtration method and a -5/3 slope was fit for an indirect measurement of epsilon. We suggest two possible mechanisms for observed flood/ebb asymmetries in the shear production of energy: wave-induced bottom roughness change or the competing effects of the barotropic and baroclinic pressure gradients. For 2001 the buoyancy flux was estimated by calculating the dissipation of temperature variance from rapidly sampled temperature time series over two different tidal cycles. The mixing efficiency tau approached 0.25 but was on average 0.05. The mixing rate depended on the flow and stratification with highest values of 200 cm2/s during maximum flow and weakest stratification and lowest values of .1 cm2/s during low flow and greater stratification. A balance of production and dissipation of energy was achieved only during ebb tide in 2001, implying that turbulent transport of TKE maybe a consideration since buoyancy dissipation is too small for 2001 and would only enhance the imbalance further in 2003 because of strong stratification that exists during the flood and ebb tide.

Diaz-Ferguson, E., Haney, A., Wares, J.P. and Silliman, B.R. 2012. Genetic structure and connectivity patterns of two Caribbean rocky-intertidal gastropods. Journal of Molluscan Studies. 78:112 - 118. (DOI: 10.1093/mollus/eyr050)

Abstract
The extent of gene flow in Caribbean marine communities has been investigated primarily in taxa from coral reef habitats, particularly in corals and reef fishes. Results from empirical population genetic studies in those taxa have indicated the presence of an east–west genetic break between 67° and 70°W longitude, and isolation of populations in the Bahamas. Hydrodynamic modelling has further suggested the presence of four connectivity regions that may contribute to genetic isolation. In this study we test for the presence of genetic structure in two gastropods (Cenchritis muricatus and Echinolittorina ziczac) from poorly sampled rocky-intertidal habitats, using mitochondrial sequence data. Significant genetic structure was found in C. muricatus (Snn = 0.29, P< 0.001; Fst = 0.022, P< 0.001), but not in E. ziczac (Snn = 0.17, P= 0.48; Fst = 0.022, P= 0.48), in spite of similar larval life histories. The pattern of differentiation does not match a simple east–west model in either species, nor a four-region model, nor do the Bahamas show evidence of isolation. However, the genetic differentiation of Bonaire from other sites that is observed in C. muricatus and E. ziczac is consistent with the previously observed isolation of this location in the trochid gastropod Cittarium pica.

Diaz-Ferguson, E., Robinson, J.D., Silliman, B.R. and Wares, J.P. 2010. Comparative Phylogeography of East Coast American Salt Marsh Communities. Estuaries and Coasts. 33:828-839. (DOI: 10.1007/s12237-009-9220-6)

Abstract
Identifying differential population structure within metacommunities is key toward describing the mechanisms that maintain biodiversity in natural systems. At both local and regional scales on the North American Atlantic coast, we assessed phylogeographic and genetic diversity patterns of six common salt marsh invertebrates using equivalent sampling schemes and sequence data from the same mitochondrial locus. In general, our results suggest little genetic structure across four previously sampled biogeographic regions and a slight increase in genetic diversity from northern to southern areas; however, two of the species (Geukensia demissa and Uca pugilator) exhibited significant differentiation between the northernmost populations and other regions, consistent with a number of previous studies. Although the minimal genetic structure recovered in this community is consistent with expectations based on the larval life history of the species examined, confirmation of this result suggests that latitudinal shifts in ecological interactions in salt marsh systems are environmentally driven, rather than due to heritable adaptation.

Dong, Y., Guerrero, S. and Moran, M.A. 2008. Using DNA technology to explore marine bacterial diversity in a coastal Georgia salt marsh. The American Biology Teacher. 70:279-283.

Abstract
An important aspect of teaching biology is to expose students to the concept of biodiversity. For this purpose, bacteria are excellent examples. Prokaryotes were the first inhabitants on Earth, surviving and even thriving under very harsh conditions as new species continuously evolved. In fact, it is believed that there are more than 5 x 10^30 prokaryotes living on Earth today (Whitman et al., 1998). Our current knowledge of these tiny organisms is very limited, and less than 1% of all bacterial species have been described (Horner-Devine et al., 2004). However, the prominent roles bacteria play in nature are not easy to overlook: Their functions range from providing essential nutrients to plants through nitrogen-fixation (such as for Rhizobium leguminosarum) to enhancement of nutrient absorption in animal intestines (such as for Escherichia coli). As a result, identifying unknown species of bacteria and extending our understanding of known ones are important tasks for 21st Century scientists.

Drake, K., Halifax, H., Adamowicz, S.C. and Craft, C.B. 2015. Carbon sequestration in tidal salt marshes of the Northeast United States. Environmental Management. 56(4):998-1008. (DOI: 10.1007/s00267-015-0568-z)

Abstract
Tidal salt marshes provide important ecological services, habitat, disturbance regulation, water quality improvement, and biodiversity, as well as accumulation and sequestration of carbon dioxide (CO2) in vegetation and soil organic matter. Different management practices may alter their capacity to provide these ecosystem services. We examined soil properties (bulk density, percent organic C, percent N), C and N pools, C sequestration and N accumulation at four marshes managed with open marsh water management (OMWM) and four marshes that were not at U.S. Fish and Wildlife National Wildlife Refuges (NWRs) on the East Coast of the United States. Soil properties (bulk density, percent organic C, percent N) exhibited no consistent differences among managed and non-OMWM marshes. Soil organic carbon pools (0-60-cm depth) also did not differ. Managed marshes contained 15.9 kg C/m(2) compared to 16.2 kg C/m(2) in non-OMWM marshes. Proportionately, more C (per unit volume) was stored in surface than in subsurface soils. The rate of C sequestration, based on Cs-137 and Pb-210 dating of soil cores, ranged from 41 to 152 g/m(2)/year. Because of the low emissions of CH4 from salt marshes relative to freshwater wetlands and the ability to sequester C in soil, protection and restoration of salt marshes can be a vital tool for delivering key ecosystem services, while at the same time, reducing the C footprint associated with managing these wetlands.

Dugan, J., Emery, K., Alber, M., Alexander, C.R. Jr., Byers, J., Gehman, A., McLenaghan, N.A. and Sojka, S. 2018. Generalizing Ecological Effects of Shoreline Armoring Across Soft Sediment Environments. Estuaries and Coasts. 41(1):180-196. (DOI: 10.1007/s12237-017-0254-x)

Abstract
Despite its widespread use, the ecological effects of shoreline armoring are poorly synthesized and difficult to generalize across soft sediment environments and structure types. We developed a conceptual model that scales predicted ecological effects of shore-parallel armoring based on two axes: engineering purpose of structure (reduce/slow velocities or prevent/stop flow of waves and currents) and hydrodynamic energy (e.g., tides, currents, waves) of soft sediment environments. We predicted greater ecological impacts for structures intended to stop as opposed to slow water flow and with increasing hydrodynamic energy of the environment. We evaluated our predictions with a literature review of effects of shoreline armoring for six possible ecological responses (habitat distribution, species assemblages, trophic structure, nutrient cycling, productivity, and connectivity). The majority of studies were in low-energy environments (51 of 88), and a preponderance addressed changes in two ecological responses associated with armoring: habitat distribution and species assemblages. Across the 207 armoring effects studied, 71% were significantly negative, 22% were significantly positive, and 7% reported no significant difference. Ecological responses varied with engineering purpose of structures, with a higher frequency of negative responses for structures designed to stop water flow within a given hydrodynamic energy level. Comparisons across the hydrodynamic energy axis were less clear-cut, but negative responses prevailed (>78%) in high-energy environments. These results suggest that generalizations of ecological responses to armoring across a range of environmental contexts are possible and that the proposed conceptual model is useful for generating predictions of the direction and relative ecological impacts of shoreline armoring in soft sediment ecosystems.

Edmonds, J.W., Weston, N.B., Joye, S.B. and Moran, M.A. 2008. Variation in Prokaryotic Community Composition as a Function of Resource Availability in Tidal Creek Sediments. Applied and Environmental Microbiology. 74(6):1836-1844. (DOI: 10.1128/AEM.00854-07)

Abstract
n anaerobic coastal sediments, hydrolytic and/or fermentative bacteria degrade polymeric material and produce labile intermediates, which are used by terminal metabolizers to complete the conversion of organic material to CO2. We used molecular approaches to evaluate the response of two bacterial terminal metabolizer groups from a coastal tidal creek sediments, sulfate reducers and methanogens, to controlled changes in carbon resource supply. Tidal creek sediment bioreactors were established in April and August 2004. For each date, intact sediment sections were continuously supplied with flowthrough seawater that was either unamended or amended with the high-molecular-weight polysaccharide dextran. Biogeochemical data indicate that the activity of fermenting bacteria and the terminal metabolizers was limited by organic carbon supply during both experiments, with a significant increase in net volatile fatty acid (VFA) production and rates of sulfate reduction and methanogenesis following dextran addition. Community composition (measured by using terminal restriction fragment length polymorphism analysis, and functional gene [dsrA, mcrA] clone libraries) changed from April to August. However, community composition was not different between amended and unamended cores within each month, despite the change in resource level. Moreover, there was no relationship between community richness and evenness with resource level. This lack of variation in community composition with C addition could be attributed to the dynamic environment these sediment communities experience in situ. Fluctuations in VFA concentrations are most likely very high, so that the dominant bacterial species must be able to outcompete other species at both high and low resource levels.

Edmonds, J.W., Weston, N.B., Joye, S.B., Mou, X. and Moran, M.A. 2009. Microbial Community Response to Seawater Amendment in Low-Salinity Tidal Sediments. Microbial Ecology. 58(3):558-568. (DOI: 10.1007/s00248-009-9556-2)

Abstract
Rising sea levels and excessive water withdrawals upstream are making previously freshwater coastal ecosystems saline. Plant and animal responses to variation in the freshwater-saline interface have been well studied in the coastal zone; however, microbial community structure and functional response to seawater intrusion remains relatively unexplored. Here, we used molecular approaches to evaluate the response of the prokaryotic community to controlled changes in porewater salinity levels in freshwater sediments from the Altamaha River, Georgia, USA. This work is a companion to a previously published study describing results from an experiment using laboratory flow-through sediment core bioreactors to document biogeochemical changes as porewater salinity was increased from 0 to 10 over 35 days. As reported in Weston et al. (Biogeochemistry, 77:375-408, 62), porewater chemistry was monitored, and cores were sacrificed at 0, 9, 15, and 35 days, at which time we completed terminal restriction fragment length polymorphism and 16S rRNA clone library analyses of sediment microbial communities. The biogeochemical study documented changes in mineralization pathways in response to artificial seawater additions, with a decline in methanogenesis, a transient increase in iron reduction, and finally a dominance of sulfate reduction. Here, we report that, despite these dramatic and significant changes in microbial activity at the biogeochemical level, no significant differences were found between microbial community composition of control vs. seawater-amended treatments for either Bacterial or Archaeal members. Further, taxa in the seawater-amended treatment community did not become more "marine-like" through time. Our experiment suggests that, as seawater intrudes into freshwater sediments, observed changes in metabolic activity and carbon mineralization on the time scale of weeks are driven more by shifts in gene expression and regulation than by changes in the composition of the microbial community.

Evans, T. and Wilson, A.M. 2017. Submarine groundwater discharge and solute transport under a transgressive barrier island. Journal of Hydrology. 547:97-110. (DOI: 10.1016/j.jhydrol.2017.01.028)

Abstract
Many recent investigations of groundwater dynamics in beaches employed groundwater models that assumed isotropic, numerically-convenient hydrogeological conditions. Real beaches exhibit local variability with respect to stratigraphy, sediment grain size and associated topographic profile, so that groundwater flow may diverge significantly from idealized models. We used a combination of hydrogeologic field methods and a variable-density, saturated-unsaturated, transient groundwater flow model to investigate SGD and solute transport under Cabretta Beach, a small transgressive barrier island seaward of Sapelo Island, Georgia. We found that the inclusion of real beach heterogeneity drove important deviations from predictions based on theoretical beaches. Cabretta Beach sustained a stronger upper saline plume than predicted due to the presence of a buried silty mud layer beneath the surface. Infiltration of seawater was greater for neap tides than for spring tides due to variations in beach slope. The strength of the upper saline plume was greatest during spring tides, contrary to recent model predictions. The position and width of the upper saline plume was highly dynamic through the lunar cycle. Our results suggest that field measurements of salinity gradients may be useful for estimating rates of tidally and density driven recirculation through the beach. Finally, our results indicate that several important biogeochemical cycles recently studied at Cabretta Beach were heavily influenced by groundwater flow and associated solute transport.

Ewers, C., Beiersdorf, A., Wieski, K., Pennings, S.C. and Zimmer, M. 2012. Predator/prey-interactions promote decomposition of low-quality detritus. Wetlands. 32:931-938. (DOI: 10.1007/s13157-012-0326-4)

Abstract
Predation on detritivores is expected to decelerate detritivore-mediated decomposition processes. In field mesocosms, we studied whether the decomposition of leaf and needle litter of live oak (Quercus virginiana) and loblolly pine (Pinus taeda), respectively, was affected by saltmarsh detritivores (Gastropoda: Littoraria irrorata and Melampus bidentatus) and predacious omnivores (Decapoda: Armases cinereum) and their interactions. Both crabs and snails alone increased decomposition (mass loss) rates of oak litter, while a combination of both resulted in the same mass loss as in animal-free controls, probably due to crabs feeding on snails rather than litter. Neither crabs nor snails alone affected mass loss of pine litter, but a combination of both significantly increased decomposition rates. Irrespective of the litter type, crabs significantly increased mortality of the snails but gained biomass only on pine litter and only when detritivorous snails were present. Our findings suggest that unidirectional facilitation of omnivorous semi-terrestrial crabs by their detritivorous prey (saltmarsh snails) promotes the decomposition of low-quality (pine) litter. On high-quality (oak) litter, by contrast, negative effects of the predator prevail, resulting in a drop of decomposition rates when crabs were present, probably owing to predation on detritivorous snails. Thus, the effects of predator/prey-interactions on decomposition processes are context-dependent and are controlled by resource quality.

Fagherazzi, S., Kirwan, M.L., Mudd, S.M., Guntenspergen, G.R., Temmerman, S., D'Alpaos, A., van de Koppel, J., Craft, C.B., Rybczyk, J., Reyes, E. and Clough, J. 2012. Numerical models of salt marsh evolution: Ecological, geomorphic and climatic factors. Reviews of Geophysics. 50(RG1002). (DOI: 10.1029/2011RG000359)

Abstract
Salt marshes are delicate landforms at the boundary between the sea and land. These ecosystems support a diverse biota that modifies the erosive characteristics of the substrate and mediates sediment transport processes. Here we present a broad overview of recent numerical models that quantify the formation and evolution of salt marshes under different physical and ecological drivers. In particular, we focus on the coupling between geomorphological and ecological processes and on how these feedbacks are included in predictive models of landform evolution. We describe in detail models that simulate fluxes of water, organic matter, and sediments in salt marshes. The interplay between biological and morphological processes often produces a distinct scarp between salt marshes and tidal flats. Numerical models can capture the dynamics of this boundary and the progradation or regression of the marsh in time. Tidal channels are also key features of the marsh landscape, flooding and draining the marsh platform and providing a source of sediments and nutrients to the marsh ecosystem. In recent years several numerical models have been developed to describe the morphogenesis and long-term dynamics of salt marsh channels. Finally, salt marshes are highly sensitive to the effects of long-term climatic change. We therefore discuss in detail how numerical models have been used to determine salt marsh survival under different scenarios of sea level rise.

Farina, J., Silliman, B.R. and Bertness, M.D. 2009. Can conservation biologists rely on established community structure rules to manage novel systems? . . Not in salt marshes. Ecological Applications. 19(2):413–422. (DOI: 10.1890/07-1000.1)

Abstract
We experimentally examined plant zonation in a previously unstudied Chilean salt marsh system to test the generality of mechanisms generating zonation of plants across intertidal stress gradients. Vertical zonation in this system is striking. The low-lying clonal succulent, Sarcocornia fruticosa, dominates the daily flooded low marsh, while intermediate elevations are dominated by the much taller Spartina densiflora. Irregularly flooded higher elevations are dominated by Schoenoplectus californicus, with the small forb, Selliera radicans, found associated with Schoenoplectus at its base. Transplant studies of all four species into each zone both with and without competition revealed the mechanisms driving these striking patterns in plant segregation. In the regularly flooded low marsh, Sarcocornia and Spartina grow in the zone that they normally dominate and are displaced when reciprocally transplanted between zones with neighbors, but without neighbors they grow well in each other’s zone. Thus, interspecific competition alone generates low marsh zonation as in some mediterranean marshes, but differently than most of the Californian marshes where physical stress is the dominant factor. In contrast, mechanisms generating high marsh patterns are similar to New England marshes. Schoenoplectus dies when transplanted to lower elevations with or without neighbors and thus is limited from the low marsh by physical stress, while Selliera grows best associated with Schoenoplectus, which shades and ameliorates potentially limiting desiccation stress. These results reveal that mechanisms driving community organization across environmental stress gradients, while generally similar among systems, cannot be directly extrapolated to unstudied systems. This finding has important implications for ecosystem conservation because it suggests that the mechanistic understanding of pattern generation necessary to manage and restore specific communities in novel habitats cannot rely exclusively on results from similar systems, and it identifies a critical role for experimental ecology in the management and conservation of natural systems and the services they provide.

Feagin, R.A., Forbrich, I., Huff, T.P., Barr, J.G., Ruiz-Plancarte, J., Fuentes, J.D., Najjar, R., Vargas, R., Vazquez-Lule, A.L., Windham-Myers, L., Kroeger, K.D., Ward, E.J., Moore, G.W., Leclerc, M.Y., Krauss, K.W., Stagg, C.L., Alber, M., Knox, S.H., Schafer, K.V.R., Bianchi, T.S., Hutchings, J.A., Nahrawi, H.B., Noormets, A., Mitra, B., Jaimes, A., Hinson, A.L., Bergamaschi, B. and King, J.S. 2020. Tidal wetland Gross Primary Production across the continental United States, 2000-2019. Globa

Abstract
We mapped tidal wetland gross primary production (GPP) with unprecedented detail for multiple wetland types across the continental United States (CONUS) at 16‐day intervals for the years 2000–2019. To accomplish this task, we developed the spatially explicit Blue Carbon (BC) model, which combined tidal wetland cover and field‐based eddy covariance tower data into a single Bayesian framework, and used a super computer network and remote sensing imagery (Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index). We found a strong fit between the BC model and eddy covariance data from 10 different towers (r2 = 0.83, p < 0.001, root‐mean‐square error = 1.22 g C/m2/day, average error was 7% with a mean bias of nearly zero). When compared with NASA's MOD17 GPP product, which uses a generalized terrestrial algorithm, the BC model reduced error by approximately half (MOD17 had r2 = 0.45, p < 0.001, root‐mean‐square error of 3.38 g C/m2/day, average error of 15%). The BC model also included mixed pixels in areas not covered by MOD17, which comprised approximately 16.8% of CONUS tidal wetland GPP. Results showed that across CONUS between 2000 and 2019, the average daily GPP per m2 was 4.32 ± 2.45 g C/m2/day. The total annual GPP for the CONUS was 39.65 ± 0.89 Tg C/year. GPP for the Gulf Coast was nearly double that of the Atlantic and Pacific Coasts combined. Louisiana alone accounted for 15.78 ± 0.75 Tg C/year, with its Atchafalaya/Vermillion Bay basin at 4.72 ± 0.14 Tg C/year. The BC model provides a robust platform for integrating data from disparate sources and exploring regional trends in GPP across tidal wetlands.

First, M.R. and Hollibaugh, J.T. 2008. Protistan bacterivory and benthic microbial biomass in an intertidal creek mudflat. Marine Ecology Progress Series. 361:59-68. (DOI: 10.3354/meps07422)

Abstract
We examined 8 sediment samples collected at 3 h intervals at Dean Creek (Sapelo Island, Georgia) to assess the impact of protist bacterivory on the standing crops of benthic bacterial biomass. The combined biomass of the benthic microalgae (BMA), bacteria, heterotrophic protists, and meiofauna ranged from 0.41 to 0.57 mg C g^–1 wet sediment (gws) in the samples examined. BMA represented >80% of total biomass and remained relatively stable throughout the study period. Bacterial biomass ranged from 28 to 91 ěg C gws^–1 (5 to 16% of total biomass) in the samples. Heterotrophic protists (mainly ciliates, flagellates, and testate amoeba) and meiofauna (mainly nematodes) each contributed small (<1% each) amounts to the total biomass. Protist grazing accounted for the loss of <1.1 and <4.7% h^–1 of the total and enzymatically active bacterial standing stock, respectively. Grazing rates were highest in the morning samples, concurrent with the highest portion of potentially active bacteria. However, there was no statistically significant change in grazing impact throughout the day and in most cases bacterivory would not reduce the standing bacterial biomass. Food web simulations demonstrate that the confluence of protist loss factors (such as meiofaunal predation) and reduced grazing at low bacterial concentrations can limit the production of bacterivorous protists and, in turn, their use of the large store of benthic bacterial biomass.

First, M.R. and Hollibaugh, J.T. 2009. The model high molecular weight DOC compound, dextran, is ingested by the benthic ciliate, Uronema marinum, but does not supplement ciliate growth. Aquatic Microbial Ecology. 57:79-87. (DOI: 10.3354/ame01338)

Abstract
Phagotrophic ciliates are capable of growth solely on dissolved compounds. Whether ciliates use dissolved compounds in the environment for growth is unclear. We investigated the ability of the marine benthic ciliate, Uronema marinum, to ingest a model high molecular weight dissolved organic carbon (HMW-DOC) compound, dextran, at concentrations typical for coastal salt marsh sediments (3µM – 3mM C). Ingestion was measured by incubating ciliates with fluorescein-labeled dextran (2,000 kDa) and measuring the fluorescence signal of the labeled compound in cells via flow cytometry. Ciliates accumulated dextran (relative to formalin-killed controls) at concentrations as low as 0.1mg l-1 dextran (3µM C). Labeled dextran accumulated in food vacuoles and near the buccal cavity, thus, the ingestion of dextran appears to be a consequence of feeding activities rather than transport across the cell membrane via parasomal sac formation. Dextran accumulation did not increase with higher bacterial ingestion rates. Instead, dextran accumulation was greatest at intermediate bacterial concentrations and grazing rates. Ciliate growth rates were measured in treatments amended with model carbon compounds – soluble starch, acetate, and glucose (3mM C, final concentrations). There was no significant increase in ciliate growth rates with these compounds in either bacteria-free or bacteria-enriched treatments. Rather, growth rates were significantly lower in treatments with DOC addition, indicating that processing of these DOC compounds may incur some energetic cost to these ciliates.

First, M.R. and Hollibaugh, J.T. 2010. Diel depth distributions of microbenthos in tidal creek sediments: high resolution mapping in fluorescently labeled embedded cores. Hydrobiologia. 655(1):149-158. (DOI: 10.1007/s10750-010-0417-2)

Abstract
Intertidal sediments experience substantial changes in temperature, salinity, and solar irradiation over short time periods. We applied the Fluorescently Labeled Embedded Core (FLEC) technique to map distribution patterns of microbenthos in tidal creek sediments. Our aims were to determine if micro-scale distributions varied over the course of a day and to test the null hypothesis that microbenthos are randomly distributed. Eight samples were collected at 3 h intervals from an intertidal sandflat on Sapelo Island, Georgia, USA. Cores were incubated with CellTracker Green (CMFDA, hereafter, CTG), a fluorogenic compounds that accumulates in metabolically active cells. Cores were embedded with epoxy and examined with laser scanning confocal microscopy. Image analysis was used to map the vertical locations of active microbenthos, which in these sediments consisted of benthic microalgae (BMA), ciliates, and flagellates. Microbenthos were abundant over the entire depth profiled (2 cm), although O2 microelectrode profiles indicate that only the top 3 mm of sediment was oxygenated during high light (1,000 µE m−2 s−1). More than 91% of organisms mapped were <22 µm in diameter and, based upon size and cell appearance, were BMA. Microbenthos accumulated in the top 1 mm at 0800 and 1100 h, corresponding to both low tide and high solar irradiation. This pattern conforms to BMA migratory rhythms determined by other methods. The standardized Morisita’s Index of dispersion determined that CTG-positive objects were significantly clumped at all time points and at each of the three spatial scales examined. This clumping pattern likely results from the heterogeneous distribution of resources, such as prey items for phagotrophs and dissolved nutrients or growth substrates for autotrophs or heterotrophs.

First, M.R. and Hollibaugh, J.T. 2010. Environmental Factors Shaping Microbial Community Structure in Salt Marsh Sediments. Marine Ecology Progress Series. 399:15-26. (DOI: 10.3354/meps08385)

Abstract
We examined benthic microbial communities in three contrasting subtidal salt marsh sediments over the course of a year to investigate the relationship between environmental conditions and benthic microbial community structure. Samples were collected monthly from a high energy, sandy beach, a tidal creek bed, and a Spartina alterniflora marsh border. The concentrations and biomasses of benthic microalgae (BMA), total and potentially active bacteria (measured by an enzyme-activated fluorogenic compound), heterotrophic protists, and metazoan meiofauna were measured at each location. Sediment grain size and porewater pH explained most of the variability in biomass distributions; variations in benthic biomass did not correlate well with temperature. There was a seasonal shift from a BMA-dominated community in the spring and summer months to bacteria-dominated communities in the autumn at all locations, when inactive bacteria were most abundant. When normalized to sediment porewater volume, benthic protists concentrations were not significantly related to sediment porosity. Benthic protist porewater concentrations (mean: 3.4x103, range: 0.1–9.3 x 103 protists ml-1) were comparable to protist concentrations in the water column. In contrast, bacteria were several orders of magnitude more concentrated in the sediments (mean: 4.2x109; range: 0.6 – 16x109 bacteria ml-1) than the water column. Low abundances of protists relative to bacteria appear to contribute to long bacterial turnover times, especially in fine grained sediments. We hypothesize that both grazing by meiofauna and low anaerobic growth efficiency lead to relatively low biomass of bacterivorous protists.

First, M.R., Miller, H.L. III, Lavrentyev, P.J., Pinckney, J.L. and Burd, A.B. 2009. Effects of microzooplankton growth and trophic interactions on herbivory in coastal and offshore environments. Aquatic Microbial Ecology. 54:255-267. (DOI: 10.3354/ame01271)

Abstract
We performed serial dilution experiments to estimate rates of gross phytoplankton growth (µ) and grazing mortality (m) in both eutrophic (Corpus Christi Bay, Texas, USA) and oligotrophic (offshore Gulf of Mexico) waters. Two parallel experiments were performed in both environments, with seawater pre-screened through 153 or 25 µm mesh to observe the responses of microzooplankton (MZP) to dilution treatments. MZP biomass changed over the duration of the experimental incubations; in several treatments, MZP net growth rates were >1 d–1. Patterns of growth varied between dilutions and initial screening size. In the eutrophic system, the ratio of phytoplankton grazing mortality rate to gross phytoplankton growth rate (m/µ) was 1.10 ± 0.54 (mean ± SD) versus 0.41 ± 0.65 when screened through 153 and 25 µm mesh, respectively. This difference was attributed to cascading trophic interactions among MZP size groups leading to suppression of the primary herbivores in the 25 µm fraction and, in turn, a lower value of m. A food web model consisting of multiple trophic levels was constructed to examine the role of MZP growth and trophic interactions on measurements of µ and m. The model, using 3 interacting groups of MZP, was able to reproduce experimental results. Model simulations demonstrated that MZP growth during incubation leads to an overestimation of m. Non-linearity in the phytoplankton growth response curves was due to MZP growth and trophic interactions in these model simulations, as variable feeding responses were not incorporated into the models. Trophic interactions among MZP can provide context to measurements of µ and m and insight into microbial food web efficiency.

First, M.R., Park, N.Y., Berrang, M.E., Meinersmann, R.J., Bernhard, J.M., Gast, R.J. and Hollibaugh, J.T. 2012. Ciliate Ingestion and Digestion: Flow Cytometric Measurements and Regrowth of a Digestion-Resistant Campylobacter jejuni. Journal of Eukaryotic Microbiology. 59(1):12 - 19. (DOI: 10.1111/j.1550-7408.2011.00589.x)

Abstract
We measured ingestion and digestion rates of the pathogenic bacterium Campylobacter jejuni by a freshwater ciliate Colpoda sp. to determine whether Campylobacter is able to resist protist digestion. Campylobacter and the nonpathogenic bacterium Pseudomonas putida LH1 were labeled with a 5-chloromethylfluorescein diacetate, which fluoresces in intact and active cells but fades when exposed to low pH environments, such as protistan food vacuoles. Ingestion and digestion rates were measured via flow cytometry as the change in ciliate fluorescence over time, which corresponded to the quantity of intracellular bacteria. The rate of Campylobacter ingestion exceeded the digestion rate. Ciliates retained labeled Campylobacter 5 h after ingestion was stopped. In contrast, ciliates grazing upon P. putida returned to baseline fluorescence within 5 h, indicating that P. putida were completely digested. The ability of intracellular Campylobacter to remain viable after ingestion was tested by sorting individual ciliates and bacterial cells into Campylobacter-selective media. Campylobacter growth occurred in 15% (± 5 SE) of wells seeded with highly fluorescent ciliates, whereas only 4% (± 1) of wells seeded with free-living Campylobacter exhibited growth. A key advantage of this approach is that it is rapid and should be applicable to other phagocytotis studies.

Fischman, H., Crotty, S.M. and Angelini, C. 2019. Optimizing coastal restoration with the stress gradient hypothesis. Proceedings of the Royal Society B. 286(1917):10. (DOI: 10.1098/rspb.2019.1978)

Abstract
Restoration efforts have been escalating worldwide in response to widespread habitat degradation. However, coastal restoration attempts notoriously vary in their ability to establish resilient, high-functioning ecosystems. Conventional restoration attempts disperse transplants in competition-minimizing arrays, yet recent studies suggest that clumping transplants to maximize facilitative interactions may improve restoration success. Here, we modify the stress gradient hypothesis to generate predictions about where each restoration design will perform best across environmental stress gradients. We then test this conceptual model with field experiments manipulating transplant density and configuration across dune elevations and latitudes. In hurricane-damaged Georgia (USA) dunes, grass transplanted in competition-minimizing (low-density, dispersed) arrays exhibited the highest growth, resilience to disturbance and dune formation in low-stress conditions. In contrast, transplants survived best in facilitation-maximizing (high-density, clumped) arrays in high-stress conditions, but these benefits did not translate to higher transplant growth or resilience. In a parallel experiment in Massachusetts where dune grasses experience frequent saltwater inundation, fewer transplants survived, suggesting that there are thresholds above which intraspecific facilitation cannot overcome local stressors. These results suggest that ecological theory can be used to guide restoration strategies based on local stress regimes, maximizing potential restoration success and return-on-investment of future efforts.

Fitzpatrick, S.M., Thompson, V.D., Poteate, A.S., Napolitano, M. and Erlandson, J.M. 2016. Marginalization of the Margins: The Importance of Smaller Islands in Human Prehistory. Special Issue: Small Islands in Prehistory. The Journal of Island and Coastal Archaeology. 11(2):155-170. (DOI: 10.1080/15564894.2016.1192568)

Abstract
Across the world's seas and oceans, archaeological research focused on islands has generally privileged those that are larger in size. Explanations for this phenomenon range from the (mis)perception by scholars that prehistoric peoples were more attracted to the presumed greater number and diversity of resources typically available on larger islands, to the ephemeral aspect of archaeological evidence on smaller land areas. These are coupled with logistical and infrastructure issues that often limit access to labor, equipment, and transportation to conduct field activities (e.g., remote atolls in the Pacific). A growing body of research demonstrates, however, that ancient peoples regularly and readily occupied and/or accessed many smaller islands for both terrestrial and marine resources. In some cases, within an archipelago, evidence shows an earlier occupation on smaller islands versus larger ones, or an attraction to the former given unique or seasonal resource availability and/or defensive capabilities. We describe cases from several areas of the world that highlight the importance of relatively small islands (∼1–500 km2) for understanding human adaptations in what many have considered to be among the most marginal of environments.

Foust, C.M., Preite, V., Schrey, A.W., Alvarez, M., Robertson, M.H., Verhoeven, K.J. and Richards, C.L. 2016. Genetic and epigenetic differences associated with environmental gradients in replicate populations of two salt marsh perennials. Special Issue: Epigenetic Studies in Ecology and Evolution. Molecular Ecology. 25:1639-1652. (DOI: 10.1111/mec.13522)

Abstract
While traits and trait plasticity are partly genetically based, investigating epigenetic mechanisms may provide more nuanced understanding of the mechanisms underlying response to environment. Using AFLP and methylation-sensitive AFLP, we tested the hypothesis that differentiation to habitats along natural salt marsh environmental gradients occurs at epigenetic, but not genetic loci in two salt marsh perennials. We detected significant genetic and epigenetic structure among populations and among subpopulations, but we found multilocus patterns of differentiation to habitat type only in epigenetic variation for both species. In addition, more epigenetic than genetic loci were correlated with habitat in both species. When we analysed genetic and epigenetic variation simultaneously with partial Mantel, we found no correlation between genetic variation and habitat and a significant correlation between epigenetic variation and habitat in Spartina alterniflora. In Borrichia frutescens, we found significant correlations between epigenetic and/or genetic variation and habitat in four of five populations when populations were analysed individually, but there was no significant correlation between genetic or epigenetic variation and habitat when analysed jointly across the five populations. These analyses suggest that epigenetic mechanisms are involved in the response to salt marsh habitats, but also that the relationships among genetic and epigenetic variation and habitat vary by species. Site-specific conditions may also cloud our ability to detect response in replicate populations with similar environmental gradients. Future studies analysing sequence data and the correlation between genetic variation and DNA methylation will be powerful to identify the contributions of genetic and epigenetic response to environmental gradients.

Franks, S.J., Richards, C.L., Gonzales, E., Cousins, J.C. and Hamrick, J.L. 2004. Multi-Scale Genetic Analysis of Uniola Paniculata (Poaceae): A Coastal Species with a Linear, Fragmented Distribution. American Journal of Botany. 91:1345-1351.

Abstract
Geographic and fine-scale population genetic structures of Uniola paniculata, the dominant coastal dune grass in the southeastern USA, were examined. The linear, naturally fragmented distribution of this native perennial was hypothesized to lead to high genetic structure and lower genetic diversity at the margin of the species range. The extensive ramet production and low seed germination of this species were also expected to cause populations to be dominated by a few large clones. At 20 sites throughout the range of the species, leaf tissue was collected from 48 individuals. Clonal structure was examined using leaf tissue collected from an additional 60 individuals, each in four patches at two sites. Starch gel electrophoresis was used to resolve 27 allozyme loci. The results indicated that Uniola had greater genetic structure (GST 5 0.304) than most other outcrossing species, indicating moderate barriers to gene flow. There was a weak but significant positive relationship between genetic distance and geographic distance, supporting an isolation-bydistance model of gene flow. There were no obvious disjunctions between regions. Genetic diversity (He) was relatively uniform throughout most of the range of the species but was lower in all western Gulf of Mexico populations. Clonal diversity varied both within and among sites, but clones were often small, suggesting that sexual reproduction and recruitment from seeds are important factors maintaining genetic diversity.

Freita, R., Schrack, E., He, Q., Silliman, B.R., Furlong, E.B., Telles, A.C. and Costa, C.S. 2016. Consumer control of the establishment of marsh foundation plants in intertidal mudflats. Marine Ecology Progress Series. 547:79-89. (DOI: 10.3354/meps11624)

Abstract
The establishment of foundation plants in bare mudflats is a critical process. While consumers are increasingly recognized to exert strong top-down control of plant performance in salt marshes, studies to date have focused on the effects of consumers on mature stands rather than on plants that are recolonizing after disturbance or where restoration has occurred. Furthermore, whether consumer-facilitated fungal infection differentially affects newly establishing plants in mudflats compared to mature stands remains poorly understood. In a salt marsh in southern Brazil, we examined the effects of herbivory by the crab Neohelice granulata and fungal infection on the survival and growth of Spartina alterniflora transplanted into mudflats. We additionally tested the effects of herbivory and fungi on newly established versus well-established stands of S. alterniflora. Highly intensive natural crab herbivory significantly reduced the development of S. alterniflora and increased its fungal infection by 50%. Light herbivory, removing only small areas of plant leaves, reduced the height growth and leaf production of directly affected tillers by about 14 to 18%, and both newly and well-established, clonally integrated stands of S. alterniflora allocated energy towards the formation of new tillers. While herbivory facilitated fungal infection and subsequent fungal damage in leaves, no significant effects of fungicide treatment or its interactions with crab grazing on S. alterniflora growth were detected, suggesting a saprophytic rather than a pathogenic role of fungi in this 3-species interaction. Here, we found that marsh grasses transplanted for restoration or those colonizing disturbance-generated mudflats may be facilitated by protection against consumers.

Freita, R., Schrack, L., Sieg, R.D., Silliman, B.R. and Costa, C. 2014. Grazing scar characteristics impact degree of fungal facilitation in /Spartina alterniflora/ leaves in a South American Salt Marsh. Brazilian Archives of Biology and Technology. 58(1):103-108. (DOI: 10.1590/S1516-8913201400030)

Abstract
Grazing scars of burrowing crabs and Hemiptera insects were simulated on leaves of the salt marsh grass Spartinaalterniflora. Simulations of crab feeding generated two-fold higher fungal (ergosterol) content in leaves incomparison to that generated by insect scar simulations (1.26 ± 0.55 and 0.57 ± 0.25 µg per cm˛, respe ctively). Thisstudy provided evidence that herbivory could facilitate microbial infection by fungi in dominant South American saltmarsh plants and indicated that specific feeding mechanisms used by different herbivores might differentially impactthe strength of this interaction

Frost, J.W., Schleicher, T. and Craft, C.B. 2009. Effects of nitrogen and phosphorus additions on primary production and invertebrate densities in a Georgia (USA) tidal freshwater marsh. Wetlands. 29(1):196-203. (DOI: 10.1672/07-79.1)

Abstract
We added nitrogen (N), phosphorus (P), and N+P to a Zizaniopsis miliacea (Giant Cutgrass) dominated tidal freshwater marsh in Georgia USA to investigate nutrient limitation of tidal freshwater marsh primary production and invertebrate densities. After two years, aboveground biomass was significantly greater in the plots receiving N (2130 g m-2), and N+P (2066 g m-2) than in the control (886 g m-2) and P (971 g m-2) only treatments. We observed no enrichment of leaf N or P in response to nutrient additions. Rather leaf N decreased and CN increased in plots receiving N, suggesting that leaf N was diluted by increased production of carbon laden structural components used to support increased plant height. NP ratios (molmol) of the plant tissue were consistently < 30 (14–27) in the treatment plots, also suggesting N limitation of primary production. Total densities of benthic invertebrates and oligochaete worms (primarily Tubificidae and Lumbriculidae) were significantly greater in the N+P plots than in the other treatments after two years of nutrient additions. There were no clear differences in diversity of benthic invertebrates among treatments. Our results suggest that tidal freshwater marsh primary and secondary production is limited or co-limited by N, and thus, like estuaries and salt marshes, are susceptible to N enrichment and eutrophication.

Garcia, E.A., Bertness, M.D., Alberti, J. and Silliman, B.R. 2011. Crab regulation of cross-ecosystem resource transfer by marine foraging fire ants. Oecologia. 166:1111-1119. (DOI: 10.1007/s00442-011-1952-x)

Abstract
Permeability of boundaries in biological systems is regulated by biotic and/or abiotic factors. Despite this knowledge, the role of biotic factors in regulating resource transfer across ecosystem boundaries has received little study. Additionally, little is known about how cross-ecosystem resource transfer affects source populations. We used experiments, observations and stable isotopes, to evaluate: (1) the proportion of intertidal-foraging black fire ant (Solenopsis richteri) diet derived from marine sources, (2) how black fire ant cross-ecosystem resource transfer is altered by the dominant bioengineer in the intertidal, a burrowing crab (Neohelice granulata), (3) the topdown impact of these terrestrial ants on a marine resource, and (4) the effect of marine resources on recipient black fire ants. We found that more than 85% of the black fire ant diet is derived from marine sources, the number of intertidal foraging ants doubles in the absence of crab burrows, and that ants cause a 50% reduction in intertidal polychaetes. Also, ant mound density is three times greater adjacent to marine systems. This study reveals that cross-ecosystem foraging terrestrial ants can clearly have strong impacts on marine resources. Furthermore, ecosystem engineers that modify and occupy habitat in these ecosystem boundaries can strongly regulate the degree of cross-ecosystem resource transfer and resultant top down impacts.

Gehman, A., Hall, R. and Byers, J. 2018. Host and parasite thermal ecology jointly determine the effect of climate warming on epidemic dynamics. Proceedings of the National Academy of Sciences. 115(4):744-749. (DOI: 10.1073/pnas.1705067115)

Abstract
Host–parasite systems have intricately coupled life cycles, but each interactor can respond differently to changes in environmental variables like temperature. Although vital to predicting how parasitism will respond to climate change, thermal responses of both host and parasite in key traits affecting infection dynamics have rarely been quantified. Through temperature-controlled experiments on an ectothermic host–parasite system, we demonstrate an offset in the thermal optima for survival of infected and uninfected hosts and parasite production. We combine experimentally derived thermal performance curves with field data on seasonal host abundance and parasite prevalence to parameterize an epidemiological model and forecast the dynamical responses to plausible future climate-warming scenarios. In warming scenarios within the coastal southeastern United States, the model predicts sharp declines in parasite prevalence, with local parasite extinction occurring with as little as 2 °C warming. The northern portion of the parasite’s current range could experience local increases in transmission, assuming no thermal adaptation of the parasite, but we find no evidence that the parasite will expand its range northward under warming. This work exemplifies that some host populations may experience reduced parasitism in a warming world and highlights the need to measure host and parasite thermal performance to predict infection responses to climate change.

Gehman, A., McLenaghan, N.A., Byers, J., Alexander, C.R. Jr., Pennings, S.C. and Alber, M. 2018. Effects of small-scale armoring and residential development on the salt marsh-upland ecotone. Estuaries and Coasts. 41(1):54-67. (DOI: 10.1007/s12237-017-0300-8)

Abstract
Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.

Gifford, S., Sharma, S., Rinta-Kanto, J. and Moran, M.A. 2011. Quantitative analysis of a deeply sequenced marine microbial metatranscriptome. International Society for Microbial Ecology. 5:461-472. (DOI: 10.1038/ismej.2010.141)

Abstract
The potential of metatranscriptomic sequencing to provide insights into the environmental factors that regulate microbial activities depends on how fully the sequence libraries capture community expression (that is, sample-sequencing depth and coverage depth), and the sensitivity with which expression differences between communities can be detected (that is, statistical power for hypothesis testing). In this study, we use an internal standard approach to make absolute (perliter) estimates of transcript numbers, a significant advantage over proportional estimates that can be biased by expression changes in unrelated genes. Coastal waters of the southeastern United States contain 1x10^12 bacterioplankton mRNA molecules per liter of seawater (~200 mRNA molecules per bacterial cell). Even for the large bacterioplankton libraries obtained in this study (~500 000 possible protein-encoding sequences in each of two libraries after discarding rRNAs andsmall RNAs from 41 million 454 FLX pyrosequencing reads), sample-sequencing depth was only 0.00001%. Expression levels of 82 genes diagnostic for transformations in the marine nitrogen, phosphorus and sulfur cycles ranged from below detection (<1x10^6 transcripts per liter) for 36 genes (for example, phosphonate metabolism gene phnH, dissimilatory nitrate reductase subunitnapA) to >2.7x10^9 transcripts per liter (ammonia transporter amt and ammonia monooxygenase subunit amoC). Half of the categories for which expression was detected, however, had too few copy numbers for robust statistical resolution, as would be required for comparative (experimental or time-series) expression studies. By representing whole community gene abundance and expressionin absolute units (per volume or mass of environment), ‘omics’ data can be better leveraged to improve understanding of microbially mediated processes in the ocean.

Givens, C., Ransom, B., Bano, N. and Hollibaugh, J.T. 2015. Comparison of the Gut Microbiomes of 12 Bony Fish and 3 Shark Species. Marine Ecology Progress Series. 518:209-223. (DOI: 10.3354/meps11034)

Abstract
We used massively parallel sequencing (pyrosequencing) of 16S rRNA genes to compare the composition of microbial communities in the guts of 12 bony fish and 3 shark species. The species analyzed encompass herbivores and carnivores with varied digestive physiologies, are classified as pelagic and demersal species, and reside in estuarine to marine environments. We also compared the gut microbial assemblages of wild and cultured Fundulus heteroclitus and of juvenile and adult Lagodon rhomboides. A total of 1 214 355 sequences were filtered, denoised, trimmed, and then sorted into operational taxonomic units (OTUs) based on 97% sequence similarity. Bacteria representing 17 phyla were found among the sampled fish, with most fish hosting between 7 and 15 phyla. Proteobacteria OTUs were present in all fish and often dominated the libraries (3.0 to 98%; average: 61%). Firmicutes were also prevalent, but at a lower relative abundance, ranging between 1.3 and 45% (average: 17%). In most cases, the gut microflora of individual fish of a given species contained many of the same OTUs; however, some species (e.g. great barracuda) shared few OTUs among the individuals sampled. Although no single OTU was shared among all fish species, many of the OTUs present in one species’ core group were also found in the core groups of other species. Several OTUs were consistently found in the guts of multiple species, suggesting that these OTUs may be important contributors to fish gut functions such as digestion, nutrient absorption, and immune response.

Goranson, C.E., Ho, C.-K. and Pennings, S.C. 2004. Environmental gradients and herbivore feeding preferences in coastal salt marshes. Oecologia. 140:591-600.

Abstract
Current theories of plant-herbivore interactions suggest that plants may differ in palatability to herbivores as a function of abiotic stress; however, studies of these theories have produced mixed results. We compared the palatability of eight common salt marsh plants that occur across elevational and salinity stress gradients to six common leaf-chewing herbivores to determine patterns of plant palatability. The palatability of every plant species varied across gradients of abiotic stress in at least one comparison, and over half of the comparisons indicated significant differences in palatability. The direction of the preferences, however, was dependent on the plant and herbivore species studied, suggesting that different types of stress affect plants in different ways, that different plant species respond differently to stress, and that different herbivore species measure plant quality in different ways. Overall, 51% of the variation in the strength of the feeding preferences could be explained by a knowledge of the strength of the stress gradient and the type of gradient, plant and herbivore studied. This suggests that the prospects are good for a more complex, conditional theory of plant stress and herbivore feeding preferences that is based on a mechanistic understanding of plant physiology and the factors underlying herbivore feeding preferences.

Gough, L., Gross, K.L., Cleland, E.E., Clark, C.M., Collins, S.L., Fargione, J.E., Pennings, S.C. and Suding, K.N. 2012. Incorporating clonal growth form clarifies the role of plant height in response to nitrogen addition. Oecologia. 169:1053-1062. (DOI: 10.1007/s00442-012-2264-5)

Abstract
Nutrient addition to grasslands consistentlycauses species richness declines and productivity increases.Competition, particularly for light, is often assumed to producethis result. Using a long-term dataset from North Americanherbaceous plant communities, we tested whether heightand clonal growth form together predict responses to fertilizationbecause neither trait alone predicted species loss in aprevious analysis. Species with a tall-runner growth formcommonly increased in relative abundance in response toadded nitrogen, while short species and those with a tallclumpedclonal growth form often decreased. The ability toincrease in size via vegetative spread across space, whilesimultaneously occupying the canopy, conferred competitiveadvantage, although typically only the abundance of a singlespecies within each height-clonal growth form significantlyresponded to fertilization in each experiment. Classifyingspecies on the basis of two traits (height and clonal growthform) increases our ability to predict species responses tofertilization compared to either trait alone in predominantlyherbaceous plant communities.

Granek, E.F., Polasky, S., Kappel, C.V., Reed, D., Stoms, D., Koch, E.W., Kennedy, C.J., Cramer, A., Hacker, S.D., Barbier, E.B., Aswani, S., Ruckelshaus, M., Perillo, M.E., Silliman, B.R., Muthiga, N., Bael, D. and Wolanski, E. 2010. Ecosystem services as a common language for coastal ecosystem-based management. Conservation Biology. 24:207-216. (DOI: 10.1111/j.1523-1739.2009.01355.x)

Abstract
Ecosystem-based management is logistically and politically challenging because ecosystems are inherently complex and management decisions affect a multitude of groups. Coastal ecosystems, which lie at the interface between marine and terrestrial ecosystems and provide an array of ecosystem services to different groups, aptly illustrate these challenges. Successful ecosystem-based management of coastal ecosystems requires incorporating scientific information and the knowledge and views of interested parties into the decision-making process. Estimating the provision of ecosystem services under alternative management schemes offers a systematic way to incorporate biogeophysical and socioeconomic information and the views of individuals and groups in the policy and management process. Employing ecosystem services as a common language to improve the process of ecosystem-based management presents both benefits and difficulties. Benefits include a transparent method for assessing trade-offs associated with management alternatives, a common set of facts and common currency on which to base negotiations, and improved communication among groups with competing interests or differing worldviews. Yet challenges to this approach remain, including predicting how human interventions will affect ecosystems, how such changes will affect the provision of ecosystem services, and how changes in service provision will affect the welfare of different groups in society. In a case study from Puget Sound, Washington, we illustrate the potential of applying ecosystem services as a common language for ecosystem-based management.

Gries, C., Budden, A., Laney, C., O'Brien, M., Servilla, M., Sheldon, W.M. Jr., Vanderbilt, K. and Vieglais, D. 2018. Facilitating and Improving Environmental Research Data Repository Interoperability. Data Science Journal. 17:22. (DOI: 10.5334/dsj-2018-022)

Abstract
Environmental research data repositories provide much needed services for data preservation and data dissemination to diverse communities with domain specific or programmatic data needs and standards. Due to independent development these repositories server their communities well, but were developed with different technologies, data models and using different ontologies. Hence, the effectiveness and efficiency of these services can be vastly improved if repositories work together adhering to a shared community platform that focuses on the implementation of agreed upon standards and best practices for curation and dissemination of data. Such a community platform drives forward the convergence of technologies and practices that will advance cross-domain interoperability. It will also facilitate contributions from investigators through standardized and streamlined workflows and provide increased visibility for the role of data managers and the curation services provided by data repositories, beyond preservation infrastructure. Ten specific suggestions for such standardizations are outlined without any suggestions for priority or technical implementation. Although the recommendations are for repositories to implement, they have been chosen specifically with the data provider/data curator and synthesis scientist in mind.

Griffin, J. and Silliman, B.R. 2011. Predator diversity stabilizes and strengthens trophic control of a keystone grazer. Biology Letters. 7:79-82. (DOI: 10.1098/rsbl.2010.0626)

Abstract
Despite the global vulnerability of predators to extinction, and the critical functional role they play in many ecosystems, there have been few realistic tests of the consequences of predator species deletion (conversely, predator diversity) in natural ecosystems. We performed a four-month field experiment in a southeastern United States salt marsh to test the role of predatory crab diversity in regulating populations of a keystone grazer that can decimate marsh vegetation at high densities. Our results revealed that a combination of this system's two resident predator species, in comparison to individual species, both stabilize and strengthen predation rates on the potent grazer. Monthly monitoring of predation rates from intense, hot summer months into the cooler autumn indicate this diversity benefit arises from predators responding differentially to changing environmental conditions across seasons. This study provides some of the first experimental field support for the insurance hypothesis from marine ecosystems, suggests that predator temporal complementarity may be more common than currently perceived, and argues for conservation of predator diversity to ensure reliable and effective control of potentially habitat-destroying grazers.

Griffin, J. and Silliman, B.R. 2011. Resource Partitioning and Why It Matters. Nature Education Knowledge. 2(1):8.

Abstract
Similar species commonly use limiting resources in different ways. Such resource partitioning helps to explain how seemingly similar species can coexist in the same ecological community without one pushing the others to extinction through competition. Understanding resource partitioning among species may help us to predict how ongoing species declines will impact the functioning of ecosystems.

Griffin, J. and Silliman, B.R. 2018. Predator size-structure and species identity determine cascading effects in a coastal ecosystem. Ecology and Evolution. (DOI: 10.1002/ece3.4571)

Abstract
Cascading consequences of predator extinctions are well documented, but impactsof perturbations to predator size‐structure and how these vary across species remainunclear. Body size is hypothesized to be a key trait governing individual predators’impact on ecosystems. Therefore, shifts in predator size‐structure should triggerecosystem ramifications which are consistent across functionally similar species.Using a US salt marsh as a model system, we tested this hypothesis by manipulatingsize class (small, medium, and large) and size diversity (combination of all three sizeclasses) within two closely related and functionally similar predatory crab speciesover 4 months. Across treatments, predators suppressed densities of a dominantgrazer and an ecosystem engineer, enhanced plant biomass, and altered sedimentproperties (redox potential and saturation). Over the metabolically equivalent experimentalpredator treatments, small size class predators had stronger average impactson response variables, and size class interacted with predator species identity todrive engineer suppression. Within both predator species, size diversity increasedcannibalism and slightly weakened the average impact. These results show that predatorimpacts in a salt marsh ecosystem are determined by both size class and sizediversity; they also highlight that size class can have species‐dependent and response‐dependent effects, underlining the challenge of generalizing trait effects.

Griffin, J., Butler, J., Soomsdat, N., Brun, K., Chejanovski, Z.A. and Silliman, B.R. 2011. Top predators suppress rather than facilitate plants in a trait-mediated tri-trophic cascade. Biology Letters. Published online. (DOI: 10.1098/rsbl.2011.0166)

Abstract
Classical ecological theory states that in tri-trophic systems, predators indirectly facilitate plants by reducing herbivore densities through consumption, while more recent work has revealed that predators can generate the same positive effect on plants non-consumptively by inducing changes in herbivore traits (e.g. feeding rates). Based on observations in US salt marshes dominated by vast monocultures of cordgrass, we hypothesized that sit-and-wait substrate-dwelling predators (crabs) could actually strengthen per capita impacts of potent grazers (snails), by non-consumptively inducing a vertical habitat shift of snails to their predation refuge high on canopy leaves that are vulnerable to grazing. A two-month field experiment supported this hypothesis, revealing that predators non-consumptively increased the mean climbing height of snails on grasses, increased grazing damage per leaf and ultimately suppressed cordgrass biomass, relative to controls. While seemingly counterintuitive, our results can be explained by (i) the vulnerability of refuge resources to grazing, and (ii) universal traits that drove the vertical habitat shift—i.e. relative habitat domains of predator and prey, and the hunting mode of the top predator. These results underline the fact that not only should we continue to incorporate non-consumptive effects into our understanding of top-down predator impacts, but we should do so in a spatially explicit manner.

Griffin, J.N., Toscano, B., Griffen, B. and Silliman, B.R. 2015. Does relative abundance modify multiple predator effects? Basic and Applied Ecology. 7:641-651. (DOI: 10.1016/j.baae.2015.05.003)

Abstract
Ecologists have long known that multiple predator species can interact with each other and thereby either strengthen or weaken overall prey regulation. With few exceptions, our understanding of such ‘multiple predator effects’ (MPEs) is based on exper-imental combinations of predators at a single relative density (usually 1:1). Because MPEs depend on interspecific interactions between predators, we hypothesized they would vary, potentially non-linearly, with predator species relative abundance. We tested this hypothesis in a southeastern US salt marsh by manipulating two species of predatory crab to generate a continuous relative abundance gradient. After four months, we evaluated the density of two shared prey species (snails and fiddler crabs) across this gradient, before explicitly testing for: (1) the presence of overall MPEs on the densities of these prey; (2) whether (and how) potential MPEs varied as a function of relative abundance; and (3) how indicators of predator–predator interactions (survivorship and limbs lost in contests) were affected by relative abundance. The final density of both prey species varied with relative abundance, but the sign of these effects switched depending on prey identity. The results failed to support an overall MPE on snail density, but final fiddler crab density was higher than expected (i.e., risk reduction, or an overall negative MPE on fiddler crab suppression). Counter to our prediction, this MPE did not vary as a function of relative abundance. Predator survivorship and limb loss indicated asymmetrical negative interactions that strongly impacted the predator species most effective at sup-pressing fiddler crabs, suggesting an explanation for the negative MPE observed for this prey species. Our findings suggest that MPEs are not always sensitive to species relative abundance, but given that shifts in predator relative abundance are frequently observed in nature, future studies should incorporate this aspect of biodiversity change into their designs wherever possible.

Guo, H. and Pennings, S.C. 2012. Mechanisms mediating plant distributions across estuarine landscapes in a low-latitude tidal estuary. Ecology. 93(1):90-100. (DOI: 10.1890/11-0487.1)

Abstract
Understanding of how plant communities are organized and will respond to global changes requires an understanding of how plant species respond to multiple environmental gradients. We examined the mechanisms mediating the distribution patterns of tidal marsh plants along an estuarine gradient in Georgia using a combination of field transplant experiments and monitoring. Our results could not be fully explained by the “competition-to-stress hypothesis” (the current paradigm explaining plant distributions across estuarine landscapes). This hypothesis states that the upstream limits of plant distributions are determined by competition, and the downstream limits by abiotic stress. We found that competition was generally strong in freshwater and brackish marshes, and that conditions in brackish and salt marshes were stressful to freshwater marsh plants, results consistent with the competition-to-stress hypothesis. Four other aspects of our results, however, were not explained by the competition-to-stress hypothesis. First, several halophytes found the freshwater habitat stressful, and performed best (in the absence of competition) in brackish or salt marshes. Second, the upstream distribution of one species was determined by the combination of both abiotic and biotic (competition) factors. Third, marsh productivity (estimated by standing biomass) was a better predictor of relative biotic interaction intensity (RII) than was salinity or flooding, suggesting that productivity is a better indicator of plant stress than salinity or flooding gradients. Fourth, facilitation played a role in mediating the distribution patterns of some plants. Our results illustrate that even apparently simple abiotic gradients can encompass surprisingly complex processes mediating plant distributions.

Guo, H. and Pennings, S.C. 2012. Post-mortem ecosystem engineering by oysters creates habitat for a rare marsh plant. Oecologia. 170:789-798. (DOI: 10.1007/s00442-012-2356-2)

Abstract
Oysters are ecosystem engineers in marine ecosystems, but the functions of oyster shell deposits in intertidal salt marshes are not well understood. The annual plant Suaeda linearis is associated with oyster shell deposits in Georgia salt marshes. We hypothesized that oyster shell deposits promoted the distribution of Suaeda linearis by engineering soil conditions unfavorable to dominant salt marsh plants of the region (the shrub Borrichia frutescens, the rush Juncus roemerianus, and the grass Spartina alterniflora). We tested this hypothesis using common garden pot experiments and field transplant experiments. Suaeda linearis thrived in Borrichia frutescens stands in the absence of neighbors, but was suppressed by Borrichia frutescens in the with-neighbor treatment, suggesting that Suaeda linearis was excluded from Borrichia frutescens stands by interspecific competition. Suaeda linearis plants all died in Juncus roemerianus and Spartina alterniflora stands, regardless of neighbor treatments, indicating that Suaeda linearis is excluded from these habitats by physical stress (likely water-logging). In contrast, Borrichia frutescens, Juncus roemerianus, and Spartina alterniflora all performed poorly in Suaeda linearis stands regardless of neighbor treatments, probably due to physical stresses such as low soil water content and low organic matter content. Thus, oyster shell deposits play an important ecosystem engineering role in influencing salt marsh plant communities by providing a unique niche for Suaeda linearis, which otherwise would be rare or absent in salt marshes in the southeastern US. Since the success of Suaeda linearis is linked to the success of oysters, efforts to protect and restore oyster reefs may also benefit salt marsh plant communities.

Guo, H., Chamberlain, S.A., Elhaik, E., Jalli, I., Lynes, A.R., Marczak, L., Sabath, N., Vargas, A., Wieski, K., Zelig, E. and Pennings, S.C. 2015. Geographic Variation in Plant Community Structure of Salt Marshes: Species, Functional and Phylogenetic Perspectives. PLOS ONE. 10(5). (DOI: 10.1371/journal.pone.0127781)

Abstract
In general, community similarity is thought to decay with distance; however, this view maybe complicated by the relative roles of different ecological processes at different geographicalscales, and by the compositional perspective (e.g. species, functional group and phylogeneticlineage) used. Coastal salt marshes are widely distributed worldwide, but nostudies have explicitly examined variation in salt marsh plant community compositionacross geographical scales, and from species, functional and phylogenetic perspectives.Based on studies in other ecosystems, we hypothesized that, in coastal salt marshes, communityturnover would be more rapid at local versus larger geographical scales; and thatcommunity turnover patterns would diverge among compositional perspectives, with agreater distance decay at the species level than at the functional or phylogenetic levels. Wetested these hypotheses in salt marshes of two regions: The southern Atlantic and GulfCoasts of the United States. We examined the characteristics of plant community compositionat each salt marsh site, how community similarity decayed with distance within individualsalt marshes versus among sites in each region, and how community similarity differedamong regions, using species, functional and phylogenetic perspectives. We found that resultsfrom the three compositional perspectives generally showed similar patterns: therewas strong variation in community composition within individual salt marsh sites across elevation;in contrast, community similarity decayed with distance four to five orders of magnitudemore slowly across sites within each region. Overall, community dissimilarity of saltmarshes was lowest on the southern Atlantic Coast, intermediate on the Gulf Coast, and highest between the two regions. Our results indicated that local gradients are relativelymore important than regional processes in structuring coastal salt marsh communities. Ourresults also suggested that in ecosystems with low species diversity, functional and phylogeneticapproaches may not provide additional insight over a species-based approach.

Guo, H., Wieski, K., Lan, Z. and Pennings, S.C. 2014. Relative influence of deterministic processes on structuring marsh plant communities varies across an abiotic gradient. Oikos. 123(2):173-178. (DOI: 10.1111/j.1600-0706.2013.00425.x)

Abstract
Understanding the processes determining community structure is one of the major goals of ecological research. Both deterministic and stochastic processes may shape community structure. The challenge is to understand the relative influence of each type of process across different environmental conditions. We investigated the influence of deterministic and stochastic processes on plant community assembly in tidal marshes across a strong abiotic (salinity) gradient in three estuaries in Georgia, USA using probabilistic Raup–Crick community dissimilarity. Our results indicated thatdeterministic processes had an increasingly important influence on structuring plant communities in salt and brackish marshes, probably due to high heterogeneity of microhabitats produced by the interplay between abiotic stress and biotic interactions. In contrast, the influence of deterministic processes on plant community assembly decreased in tidal freshwater marshes, suggesting an increasingly important role of stochastic processes in plant community assembly in tidal freshwater marshes, probably due to the higher species richness, higher recruitment from seed, and lower levels of abiotic stress in these habitats. At the estuarine scale (across tidal freshwater, brackish and salt marshes in each estuary), our results suggested that deterministic processes also had a relatively important influence on shaping plant communitystructure. Our results illustrated that plant community structure in tidal marshes is influenced by both deterministic and stochastic processes, but that the relative influence of these two types of processes varies across estuarine landscapes.

Guo, H., Zhang, Y., Lan, Z. and Pennings, S.C. 2013. Biotic interactions mediate the expansion of black mangrove (Avicennia germinans) into salt marshes under climate change. Global Change Biology. 19:2765 - 2744. (DOI: 10.1111/gcb.12221)

Abstract
Many species are expanding their distributions to higher latitudes due to global warming. Understanding the mechanisms underlying these distribution shifts is critical for better understanding the impacts of climate changes. The climate envelope approach is widely used to model and predict species distribution shifts with changing climates. Biotic interactions between species, however, may also influence species distributions, and a better understanding of biotic interactions could improve predictions based solely on climate envelope models. Along the northern Gulf of Mexico coast, USA, subtropical black mangrove (Avicennia germinans) at the northern limit of its distribution grows sympatrically with temperate salt marsh plants in Florida, Louisiana, and Texas. In recent decades, freeze‐free winters have led to an expansion of black mangrove into salt marshes. We examined how biotic interactions between black mangrove and salt marsh vegetation along the Texas coast varied across (i) a latitudinal gradient (associated with a winter‐temperature gradient); (ii) the elevational gradient within each marsh (which creates different marsh habitats); and (iii) different life history stages of black mangroves (seedlings vs. juvenile trees). Each of these variables affected the strength or nature of biotic interactions between black mangrove and salt marsh vegetation: (i) Salt marsh vegetation facilitated black mangrove seedlings at their high‐latitude distribution limit, but inhibited black mangrove seedlings at lower latitudes; (ii) mangroves performed well at intermediate elevations, but grew and survived poorly in high‐ and low‐marsh habitats; and (iii) the effect of salt marsh vegetation on black mangroves switched from negative to neutral as black mangroves grew from seedlings into juvenile trees. These results indicate that the expansion of black mangroves is mediated by complex biotic interactions. A better understanding of the impacts of climate change on ecological communities requires incorporating context‐dependent biotic interactions into species range models.

Gustafson, D.J., Kilheffer, J. and Silliman, B.R. 2006. Relative impacts of Littoraria irrorata and Prokelisia marginata on Spartina alterniflora growth. Estuaries and Coasts. 29(4):639-644.

Abstract
Spartina alterniflora salt marshes along the southeastern United States are some of the most productive and well studied ecosystems in the world. The role of physicochemical forces in regulating Spartina growth is well understood, while the importance of grazers remains less clear. Recent studies have shown that the abundant marsh periwinkle, Littoraria irrorata, can exert strong control over Spartina through its grazing activities, but relatively little is known about its relative effects in comparison to other marsh plant consumers. To test the relative importance of snail and insect consumers on Spartina biomass, we conducted a 7-mo field experiment testing top-down regulation of Spartina with all combinations of L. irrorata (removed, control, c. 215 periwinkles m22) and Spartina planthopper, Prokelisia marginata (removed, control). Snail removal resulted in a 50% increase in Spartina biomass while removal of planthoppers had no detectable effect. Planthopper density also increased by 50% when snails were excluded. In this South Carolina marsh, L. irrorata exerts a stronger top-down control of Spartina than P. marginata. These results indicate trophic cascade regulation of Spartina salt marsh is more likely to occur through the predator(s)-Littoraria-plant interaction than through the predator(s)-Prokelisia-plant relationship.

Hardy, D., Milligan, R.A. and Heynen, N. 2017. Racial coastal formation: The environmental injustice of colorblind adaptation planning for sea-level rise. Geoforum. 87(December 2017):62-72. (DOI: 10.1016/j.geoforum.2017.10.005)

Abstract
The United States’ deeply racialized history currently operates below the surface of contemporary apolitical narratives on vulnerability mitigation and adaptation to sea-level rise. As communities, regulatory agencies, and policy-makers plan for rising seas, it is important to recognize the landscapes of race and deep histories of racism that have shaped the socio-ecological formations of coastal regions. If this history goes unrecognized, what we label colorblind adaptation planning is likely to perpetuate what Rob Nixon calls the “slow violence” of environmental racism, characterized by policies that benefit some populations while abandoning others. By colorblind adaptation planning, we refer to vulnerability mitigation and adaptation planning projects that altogether overlook racial inequality—or worse dismiss its systemic causes and explain away racial inequality by attributing racial disparities to non-racial causes. We contend that responses to sea-level rise must be attuned to racial difference and structures of racial inequality. In this article, we combine the theory of racial formation with the geographical study of environmental justice and point to the ways racial formations are also environmental. We examine vulnerability to sea-level rise through the process of racial coastal formation on Sapelo Island, Georgia, specifically analyzing its deep history, the uneven racial development of land ownership and employment, and barriers to African American participation and inclusion in adaptation planning. Racial coastal formation’s potential makes way for radical transformation in climate change science not only in coastal areas, but other spaces as situated territorial racial formations.

Hauer, M., Evans, J. and Alexander, C.R. Jr. 2015. Sea-Level Rise and Sub-County Population Projections in Coastal Georgia. Population and the Environment. 37:44-62. (DOI: 10.1007/s11111-015-0233-8)

Abstract
It is increasingly apparent that stressors associated with anthropocentric climate change are likely to have dramatic effects on future human settlement patterns. Although sea-level rise is one of the best understood implications of climate change, geographically precise estimation of potential population displacement due to tidewater inundation has proven remarkably problematic. At least within the USA, these problems partially stem from methodological limitations of population projection methodology at sub-county scales. Using a case study of coastal Georgia, USA, this paper develops and demonstrates a new housing unitbased population projection method that is applied at the sub-county scale of Census Block Groups. These projections are then overlaid with spatiotemporally explicit assessments of future sea-level rise inundation provided through the Sea Level Affecting Marsh Model (SLAMM). We find that between 62,000 and 159,000 people are at risk of between 1 and 2 m of sea-level rise by 2100 in coastal Georgia.

Hawkes, A., Kemp, A., Donnelly, J., Horton, B., Peltier, W., Cahill, N., Hill, D., Ashe, E. and Alexander, C. 2016. Relative Sea-Level Change in Northeastern Florida (USA) During the Last ~8.0 KA. Quaternary Science Reviews. (DOI: 10.1016/j.quascirev.2016.04.016)

Abstract
An existing database of relative sea-level (RSL) reconstructions from the U.S. Atlantic coast lacked valid sea-level index points from Georgia and Florida. This region lies on the edge of the collapsing forebulge of the former Laurentide Ice Sheet making it an important location for understanding glacio-isostatic adjustment and the history of ice-sheet melt. To address the paucity of data, we reconstruct RSL in northeastern Florida (St. Marys) over the last ∼8.0 ka from samples of basal salt-marsh sediment that minimize the influence of compaction. The analogy between modern salt-marsh foraminifera and their fossil counterparts preserved in the sedimentary record was used to estimate paleomarsh surface elevation. Sample ages were determined by radiocarbon dating of identifiable and in-situ plant macrofossils. This approach yielded 25 new sea-level index points that constrain a ∼5.7 m rise in RSL during the last ∼8.0 ka. The record shows that no highstand in sea level occurred in this region over the period of the reconstruction. We compared the new reconstruction to Earth-ice models ICE 6G-C VM5a and ICE 6G-C VM6. There is good fit in the later part of the Holocene with VM5a and for a brief time in the earlier Holocene with VM6. However, there are discrepancies in model-reconstruction fit in the early to mid Holocene in northeastern Florida and elsewhere along the Atlantic coast at locations with early Holocene RSL reconstructions. The most pronounced feature of the new reconstruction is a slow down in the rate of RSL rise from approximately 5.0 to 3.0 ka. This trend may reflect a significant contribution from local-scale processes such as tidal-range change and/or change in base flow of the St. Marys River in response to paleoclimate changes. However, the spatial expression (local vs. regional) of this slow down is undetermined and corroborative records are needed to establish its geographical extent.

He, Q. and Silliman, B.R. 2015. Biogeographic consequences of nutrient enrichment for plant-herbivore interactions in coastal wetlands. Ecology Letters. 18:462–471. (DOI: 10.1111/ele.12429)

Abstract
A major challenge in ecology is to understand broadscale trends in the impact of environmental change. We provide the first integrative analysis of the effects of eutrophication on plants, herbivores, and their interactions in coastal wetlands across latitudes. We show that fertilisation strongly increases herbivory in salt marshes, but not in mangroves, and that this effect increases with increasing latitude in salt marshes. We further show that stronger nutrient effects on plant nitrogen concentration at higher latitudes is the mechanism likely underlying this pattern. This biogeographic variation in nutrient effects on plant–herbivore interactions has consequences for vegetation, with those at higher latitudes being more vulnerable to consumer pressure fuelled by eutrophication. Our work provides a novel, mechanistic understanding of how eutrophication affects plant–herbivore systems predictably across broad latitudinal gradients, and highlights the power of incorporating biogeography into understanding large-scale variability in the impacts of environmental change.

He, Q. and Silliman, B.R. 2016. Consumer control as a common driver of coastal vegetation worldwide. Ecological Monographs. 86(3):278-294. (DOI: 10.1002/ecm.1221)

Abstract
Rapid, global, anthropogenic alteration of food webs in ecosystems necessitates a better understanding of how consumers regulate natural communities. We provide a global synthesis of consumer control of vegetation in coastal wetlands, where the domineering role of physical factors such as nutrient and salinity, rather than consumers, has been emphasized for decades. Using a data set of 1748 measures of consumer effects reported in 443 experiments/observations on all continents except Antarctica, we examine the generality of consumer control in salt marshes and mangroves globally. Our analyses show that salt marsh herbivores, including insects, snails, crabs, waterfowl, small mammals, and livestock, generally and often strongly suppress plant survival, aboveground biomass, and height, while their effects on plant density, belowground biomass, reproduction, and cover are more variable. These effects occur in forbs, grasses, and shrubs, and in both seedlings and adult plants. Herbivores additionally affect plant nutrient stoichiometry, and mediate plant interactions, though their effects on plant diversity are less consistent. Higher trophic levels also affect plants, as predators facilitate plant growth through trophic cascades that suppress grazer abundance and grazing rate. In mangroves, there are also signs of consumer control, though the relatively few studies available have often focused on mangrove propagules and seedlings rather than adults. Our analyses further reveal that the strength of consumer control is regulated by many physical factors. Nutrient, disturbance, and flooding, for example, amplify the negative effects of herbivores. Along latitudinal gradients, increased temperature enhances the negative effects of ectothermic herbivores, but has no effect on those of endothermic herbivores. Consumer control of coastal plants is also apparent across study methodologies: in field and laboratory settings, in observational studies, in consumer exclusion and addition experiments, in natural and transplanted plants, and in experiments of various durations. The role of consumer control in coastal vegetation worldwide highlights the need to better recognize and theoretically conceptualize both top-down and bottom-up forcing and their interactions in coastal wetlands. Improved understanding and conservation of coastal wetlands will only occur if we incorporate what the science has revealed: trophic feedbacks are an important and pervasive determinant of coastal plant communities.

He, Q. and Silliman, B.R. 2019. Climate Change, Human Impacts, and Coastal Ecosystems in the Anthropocene. Current Biology. 29(19):1021-1035. (DOI: 10.1016/j.cub.2019.08.042)

Abstract
Coastal zones, the world’s most densely populated regions, are increasingly threatened by climate change stressors — rising and warming seas, intensifying storms and droughts, and acidifying oceans. Although coastal zones have been affected by local human activities for centuries, how local human impacts and climate change stressors may interact to jeopardize coastal ecosystems remains poorly understood. Here we provide a review on interactions between climate change and local human impacts (e.g., interactions between sea level rise and anthropogenic land subsidence, which are forcing Indonesia to relocate its capital city) in the coastal realm. We highlight how these interactions can impair and, at times, decimate a variety of coastal ecosystems, and examine how understanding and incorporating these interactions can reshape theory on climate change impacts and ecological resilience. We further discuss implications of interactions between climate change and local human impacts for coastal conservation and elucidate the context when and where local conservation is more likely to buffer the impacts of climate change, attempting to help reconcile the growing debate about whether to shift much of the investment in local conservation to global CO2 emission reductions. Our review underscores that an enhanced understanding of interactions between climate change and local human impacts is of profound importance to improving predictions of climate change impacts, devising climate-smart conservation actions, and helping enhance adaption of coastal societies to climate change in the Anthropocene.

He, Q., Bertness, M.D., Bruno, J.F., Li, B., Chen, G., Coverdale, T.C., Alteiri, A., Bai, J., Sun, T., Pennings, S.C., Liu, J., Ehrlich, P.R. and Cui, B. 2014. Economic development and coastal ecosystem change in China. Scientific Reports. 4(5995):9. (DOI: 10.1038/srep05995)

Abstract
Despite their value, coastal ecosystems are globally threatened by anthropogenic impacts, yet how these impacts are driven by economic development is not well understood. We compiled a multifaceted dataset to quantify coastal trends and examine the role of economic growth in China's coastal degradation since the 1950s. Although China's coastal population growth did not change following the 1978 economic reforms, its coastal economy increased by orders of magnitude. All 15 coastal human impacts examined increased over time, especially after the reforms. Econometric analysis revealed positive relationships between most impacts and GDP across temporal and spatial scales, often lacking dropping thresholds. These relationships generally held when influences of population growth were addressed by analyzing per capita impacts, and when population density was included as explanatory variables. Historical trends in physical and biotic indicators showed that China's coastal ecosystems changed little or slowly between the 1950s and 1978, but have degraded at accelerated rates since 1978. Thus economic growth has been the cause of accelerating human damage to China's coastal ecosystems. China's GDP per capita remains very low. Without strict conservation efforts, continuing economic growth will further degrade China's coastal ecosystems.

He, Y., Li, X., Craft, C.B., Ma, Z. and Sun, Y. 2011. Relationships between vegetation zonation and environmental factors in newly formed tidal marshes of the Yangtze River estuary. Wetlands Ecology and Management. 19:341-349.

Abstract
The Yangtze River delta is characterized by rapidly accreting sediments that form tidal flats that are quickly colonized by emergent vegetation including Scirpus mariqueter and the invasive species Spartina alterniflora. We measured soil surface elevation, water table depth, soil salinity, water content and compaction in the tidal flat, the Scirpus and Spartina zones and their borders to identify relationships between environmental factors and colonization by Scirpus and Spartina. With increasing elevation from tidal flat to Spartina, inundation frequency and duration, moisture and depth to water table decreased whereas soil salinity, temperature and compaction increased. High soil moisture and groundwater and low salinity were the characteristics of the tidal flat and its border with Scirpus. The Spartina zone and its border with Scirpus were characterized by greater salinity and elevation relative to the other zones. Our findings suggest that soil salinity controls patterns of plant zonation in the newly formed tidal salt marshes whereas elevation is of secondary importance. Our results suggest that patterns of vegetation zonation in tidal marshes of the Yangtze River delta are controlled by environmental factors, especially (low) salinity that favors colonization by Scirpus in the lower elevations of the marsh.

He, Y., Widney, S., Ruan, M., Herbert, E., Li, X. and Craft, C.B. 2016. Accumulation of soil carbon drives denitrification potential and labincubatedgas production along a chronosequence of salt marshdevelopment. Estuarine, Coastal and Shelf Science. 172(5):72-80. (DOI: 10.1016/j.ecss.2016.02.002)

Abstract
We measured sediment organic carbon and nitrogen accumulation and rates of denitrification enzyme activity and greenhouse gas (CO2, CH4, N2O) production from slurries of sediments of a mudflat that formed in 2002, a young (8-year-old) natural Spartina alterniflora salt marsh that developed on part of the mudflat, and four mature (>200 years old) salt marshes in southeastern Georgia to examine microbial processes related to carbon (C) and nitrogen (N) cycling during succession from mudflat to mature marsh. Soil organic C and N and C: N ratio (0–30 cm) increased across the chronosequence from mudflat (791 ± 35 g C/m2, 125 ± 17 g N/m2) to young marsh (2520 ± 131 g C/m2, 190 ± 10 g N/m2) to mature marshes (5827 ± 250 g C/m2, 372 ± 20 g N/m2). After 8 years of colonization by S. alterniflora, sediment organic carbon increased 3.2 times, and nitrogen increased 1.5 times relative to the mudflat. The high rate of organic C and N accumulation based on time series measurements (188 g C/m2/yr, 7.8 g N/m2/yr) and feldspar marker layers (359 g C/m2/yr, 26.2 g N/m2/yr) was attributed to high accretion (3 cm/yr) in this low elevation (0.18 m NAVD88) emerging marsh. Carbon dioxide production increased with increasing sediment organic C from mudflat to mature marshes. Un-amended denitrification enzyme activity, measured in slurry incubations, ranged from an average of 0.020 ± 0.005 µg g−1 hr−1 in the mature marshes to 0.094 ± 0.03 µg g−1 hr−1 in the young marsh. We also measured denitrification potential in slurry incubations amended with C (glucose), N (nitrate), and C + N to assess the potential for substrate limitations. Denitrification potential in the mudflat did not show strong nutrient limitation. In the young marsh, denitrification potential was C-limited, and in the mature marsh, it was co-limited by C and N. In July samples, CO2 production showed a statistically significant increase with age from the mudflat to the mature marshes. However, in both months, CO2 production efficiency (expressed on a per g C basis) was significantly higher in the mudflat sediment slurries than in the young marsh and mature marsh samples. Spartina colonization of mudflats and the subsequent accumulation of organic matter are key to enriching sediment organic C and N pools that control microbial heterotrophy, particularly denitrification and CO2 production, which play important roles in marsh C and N cycling.

Hensel, M.S. and Silliman, B.R. 2013. Consumer diversity across kingdoms supports multiple functions in a coastal ecosystem. Proceedings of the National Academy of Sciences of the United States of America. 110(51):20621-20626. (DOI: 10.1073/pnas.1312317110)

Abstract
The global biodiversity crisis impairs the valuable benefits ecosystems provide humans. These nature-generated benefits are defined by a multitude of different ecosystem functions that operate simultaneously. Although several studies have simulated species loss in communities and tracked the response of single functions such as productivity or nutrient cycling, these studies have involved relatively similar taxa, and seldom are strikingly different functions examined. With the exception of highly managed ecosystems such as agricultural fields, rarely are we interested in only one function being performed well. Instead, we rely on ecosystems to deliver several different functions at the same time. Here, we experimentally investigated the extinction impacts of dominant consumers in a salt marsh. These consumers are remarkably phylogenetically diverse, spanning two kingdoms (i.e., Animalia and Fungi). Our field studies reveal that a diverse consumer assemblage significantly enhances simultaneous functioning of disparate ecosystem processes (i.e., productivity, decomposition, and infiltration). Extreme functional and phylogenetic differences among consumers underlie this relationship. Each marsh consumer affected at least one different ecosystem function, and each individual function was affected by no more than two consumers. The implications of these findings are profound: If we want ecosystems to perform many different functions well, it is not just number of species that matter. Rather, the presence of species representing markedly different ecologies and biology is also essential to maximizing multiple functions. Moreover, this work emphasizes the need to incorporate both microcomponents and macrocomponents of food webs to accurately predict biodiversity declines on integrated-ecosystem functioning.

Herbert, E., Boon, P., Burgin, A.J., Neubauer, S.C., Franklin, R.B., Ardon, M., Hopfensperger, K.N., Lamers, L. and Gell, P. 2015. A global perspective on wetland salinization: Ecological consequences of a growing threat to freshwater wetlands. Ecosphere. 6(10)(206):1-43. (DOI: 10.1890/ES14-00534.1)

Abstract
Salinization, a widespread threat to the structure and ecological functioning of inland and coastal wetlands, is currently occurring at an unprecedented rate and geographic scale. The causes of salinization are diverse and include alterations of freshwater flows, land-clearance, irrigation, sea level rise, wastewater effluent, applications of de-icing salts, and storm surges. Climate change and anthropogenic modifications to the hydrologic cycle are expected to further increase the extent and severity of wetland salinization. Salinization alters the fundamental physicochemical nature of the soil-water environment, increasing ionic concentrations and altering chemical equilibria and mineral solubility. Increased concentrations of solutes, especially sulfate, alter the biogeochemical cycling of major elements including carbon, nitrogen, phosphorus, sulfur, iron, and silica. The effects of salinization on wetland biogeochemistry typically include decreased inorganic nitrogen removal (with implications for water quality and climate regulation), decreased carbon storage (with implications for climate regulation and wetland accretion), and increased generation of toxic sulfides (with implications for nutrient cycling and the health/functioning of wetland biota). Indeed, increased salt and sulfide levels induce physiological stress in wetland biota and ultimately can result in large shifts in wetland communities and their associated ecosystem functions. The productivity and composition of freshwater species assemblages will be highly altered, and there is a high potential for the disruption of existing interspecific interactions. Although there is a wealth of information on how salinization impacts individual ecosystem components, relatively few studies have addressed the complex and often non-linear feedbacks that determine ecosystem-scale responses or how wetland salinization will affect landscape-level processes. While the salinization of wetlands may be unavoidable in many cases, these systems may also prove to be a fertile testing ground for broader ecological theories including (but not limited to): alternative stable states and tipping points, trophic cascades, disturbance-recovery, and the role of historical events and landscape context in driving community response to disturbance.

Herbert, E., Schubauer-Berigan, J.P. and Craft, C.B. 2018. Differential effects of chronic and acute simulated seawater intrusion on tidal freshwater marsh carbon cycling. Biogeochemistry. Published online 24-Mar-2018. (DOI: 10.1007/s10533-018-0436-z)

Abstract
Tidal freshwater ecosystems experience acute seawater intrusion associated with periodic droughts, but are expected to become chronically salinized as sea level rises. Here we report the results from an experimental manipulation in a tidal freshwater Zizaniopsis miliacea marsh on the Altamaha River, GA where diluted seawater was added to replicate marsh plots on either a press (constant) or pulse (2 months per year) basis. We measured changes in porewater chemistry (SO4 2-, Cl-, organic C, inorganic nitrogen and phosphorus), ecosystem CO2 and CH4 exchange, and microbial extracellular enzyme activity. We found that press (chronic) seawater additions increased porewater chloride and sulfate almost immediately, and ammonium and phosphate after 2–4 months. Chronic increases in salinity also decreased net ecosystem exchange, resulting in reduced CO2 and CH4 emissions from press plots. Our pulse treatment, designed to mimic natural salinity incursion in the Altamaha River (September and October), temporarily increased porewater ammonium concentrations but had few lasting effects on porewater chemistry or ecosystem carbon balance. Our findings suggest that long-term, chronic saltwater intrusion will lead to reduced C fixation and the potential for increased nutrient (N, P) export while acute pulses of saltwater will have temporary effects.

Herbert, E., Schubauer-Berigan, J.P. and Craft, C.B. 2018. Effects of ten years of nitrogen and phosphorus fertilization in tidal freshwater marshes. Limnology and Oceanography. (in review)

Herbert, E., Schubauer-Berigan, J.P. and Craft, C.B. 2020. Effects of ten years of nitrogen and phosphorus fertilization on carbon and nutrient cycling in a tidal freshwater marsh. Limnology and Oceanography. (in press)

Abstract
Tidal freshwater marshes can protect downstream ecosystems from eutrophication by intercepting excess nutrient loads, but recent studies in salt marshes suggest nutrient loading compromises their structural and functional integrity. Here, we present data on changes in plant biomass, microbial biomass and activity, and soil chemistry from plots in a tidal freshwater marsh on the Altamaha River (GA) fertilized for 10 yr with nitrogen (+N), phosphorus (+P), or nitrogen and phosphorus (+NP). Nitrogen alone doubled aboveground biomass and enhanced microbial activity, specifically rates of potential nitrification, denitrification, and methane production measured in laboratory incubations. Phosphorus alone increased soil P and doubled microbial biomass but did not affect microbial processes. Nitrogen or P alone decreased belowground biomass and soil carbon (C) whereas +NP increased aboveground biomass, microbial biomass and N cycling, and N, P, and C assimilation and burial more than either nutrient alone. Our findings suggest differential nutrient limitation of tidal freshwater macrophytes by N and microbes by P, similar to what has been observed in salt marshes. Macrophytes outcompete microbes for P in response to long‐term N and P additions, leading to increased soil C storage through increased inputs of belowground biomass relative to N and P added singly. The susceptibility of tidal freshwater marshes to long‐term nutrient enrichment and, hence their ability to mitigate eutrophication will depend on the quantity and relative proportion of N vs. P entering estuaries and tidal wetlands.

Herrmann, M., Najjar, R.G., Kemp, M., Alexander, R.B., Boyer, E.W., Cai, W.-J., Griffith, P.C., Kroeger, K.D., McCallister, S.L. and Smith, R.A. 2015. Net ecosystem production and organic carbon balance of U.S. East Coast estuaries: A synthesis approach. Global Biogeochemical Cycles. 29(1):96-111. (DOI: 10.1002/2013GB004736)

Abstract
Net ecosystem production (NEP) and the overall organic carbon budget for the estuaries along the East Coast of the United States are estimated. We focus on the open estuarine waters, excluding the fringing wetlands. We developed empirical models relating NEP to loading ratios of dissolved inorganic nitrogen to total organic carbon, and carbon burial in the sediment to estuarine water residence time and total nitrogen input across the landward boundary. Output from a data-constrained water quality model was used to estimate inputs of total nitrogen and organic carbon to the estuaries across the landward boundary, including fluvial and tidal-wetland sources. Organic carbon export from the estuaries to the continental shelf was computed by difference, assuming steady state. Uncertainties in the budget were estimated by allowing uncertainties in the supporting model relations. Collectively, U.S. East Coast estuaries are net heterotrophic, with the area-integrated NEP of −1.5 (−2.8, −1.0) Tg C yr−1 (best estimate and 95% confidence interval) and area-normalized NEP of −3.2 (−6.1, −2.3) mol C m−2 yr−1. East Coast estuaries serve as a source of organic carbon to the shelf, exporting 3.4 (2.0, 4.3) Tg C yr−1 or 7.6 (4.4, 9.5) mol C m−2 yr−1. Organic carbon inputs from fluvial and tidal-wetland sources for the region are estimated at 5.4 (4.6, 6.5) Tg C yr−1 or 12 (10, 14) mol C m−2 yr−1 and carbon burial in the open estuarine waters at 0.50 (0.33, 0.78) Tg C yr−1 or 1.1 (0.73, 1.7) mol C m−2 yr−1. Our results highlight the importance of estuarine systems in the overall coastal budget of organic carbon, suggesting that in the aggregate, U.S. East Coast estuaries assimilate (via respiration and burial) ~40% of organic carbon inputs from fluvial and tidal-wetland sources and allow ~60% to be exported to the shelf.

Higinbotham, C.B., Alber, M. and Chalmers, A.G. 2004. Analysis of Tidal Marsh Vegetation Patterns in Two Georgia Estuaries Using Aerial Photography and GIS. Estuaries. 27(4):670-683.

Abstract
Aerial photographs and GIS analysis were used to map the distribution of tidal marsh vegetation along the salinity gradients of the estuaries of the Altamaha and Satilla Rivers in coastal Georgia. Vegetation maps were constructed from 1993 USGS DOQQs, 1:77000-scale color infrared photographs taken in 1974 and 1:24000-scale black and white photographs taken in 1953. Changes between years were identified using a GIS overlay analysis. Four vegetation classifications were identified and groundtruthed with field surveys: salt marsh (areas containing primarily Spartina alterniflora); brackish marsh (S. cynosuroides and S. alterniflora), Juncus (Juncus roemerianus), and fresh marsh (Zizania aquatica, Zizaniopsis miliacae, and others). Although the inland extent of each marsh zone was further upstream in the Satilla than the Altamaha, they corresponded with the same salinities in each estuary: the division between salt and brackish marsh occurred where high tide salinities averaged 15 psu; Juncus began at 21 psu; and the division between fresh marsh and both Juncus and brackish marsh occurred at 1 psu. 23% of the 6,786 ha of tidal marsh vegetation mapped in the Altamaha and 13% of the 10,205 ha mapped in the Satilla remained the same between 1953 and 1993, although this does not include the area that changed in the intervening year (1974). Juncus was the dominant classification in the intermediate regions of both estuaries, and shifts between Juncus and either brackish or salt marsh constituted the primary vegetation change between 1953 and 1993 (87% of the changes observed in the Altamaha and 95% of those in the Satilla). This analysis suggests that the broad distribution of tidal marsh vegetation along these two estuaries is driven by salinity, but that at the local scale these are dynamic systems with a larger complex of factors affecting the frequently changing borders of vegetation patches.

Hladik, C.M. and Alber, M. 2012. Accuracy assessment and correction of a LIDAR-derived salt marsh digital elevation model. Remote Sensing of the Environment. 121:234-235. (DOI: 10.1016/j.rse.2012.01.018)

Abstract
Accurate habitat mapping in salt marshes is critical for both management and conservation goals. Information on marsh elevation is important to coastal managers, particularly for flood inundation mapping, coastal hazard assessments and modeling sea level rise. Elevation is also an important determinant of the frequency and duration of tidal flooding, which in turn affects species patterns in marshes: elevation differences of less than 10 cm can affect plant distributions and productivity. Light Detection and Ranging (LIDAR) can provide synoptic elevation information in many environments, but its accuracy in salt marshes is limited by a combination of sensor resolution, instrument errors, and poor laser penetration in dense vegetation. This means that uncorrected digital elevation models (DEM) are generally not accurate enough to distinguish elevation changes in salt marsh environments at the resolution that can be used to determine tidal flooding or vegetation patterns. In this study, we used a LIDAR-derived DEM for the salt marshes surrounding Sapelo Island, GA obtained with a state-of- the- art Optech Gemini ALTM LIDAR system with a high laser pulse rate frequency of 125 kHz and evaluated its accuracy with elevations collected using real time kinematic (RTK) GPS. We found that LIDAR offsets for different cover classes ranged from 0.03 to 0.25 m in comparison to the RTK ground truth data, with the larger offsets for taller vegetation. We developed species-specific correction factors for ten cover classes and used these correction factors to modify the LIDAR-derived DEMs in four test areas of the study domain. Application of the derived correction factors greatly improved the accuracy of the LIDAR DEM, reducing the overall mean LIDAR error from 0.10 ± 0.12 (SD) to -0.01 ± 0.09 m (SD), and the Root Mean Square Error from 0.16 m to 0.10 m. In the corrected DEM, the elevations of all vegetation classes were no longer significantly different than the true RTK ground elevations. Our results suggest that these types of corrections can greatly improve the accuracy of DEMs in salt marshes and further emphasize the importance of accuracy assessments before LIDAR data are used, especially in environments such as salt marshes where small differences in elevation can have significant effects on inundation patterns and plant distributions.

Hladik, C.M. and Alber, M. 2014. Classification of salt marsh vegetation using edaphic and remote sensing-derived variables. Estuarine, Coastal and Shelf Sciences. 141:47 - 57. (DOI: 10.1016/j.ecss.2014.01.011)

Abstract
Salt marsh plant communities are known for their striking patterns of vertical zonation. Two of the most important edaphic parameters that affect species distribution patterns are soil salinity and waterlogging, both of which are related to topographical variations and distance to the water. The primary objective of this study was to evaluate whether information on elevation and distance derived through remote sensing could be used to predict plant distributions in a southeastern salt marsh. We classified four marsh vegetation classes (tall Spartina alterniflora, medium S. alterniflora/short S. alterniflora, marsh meadow, and Borrichia frutescens/Juncus roemerianus) based on landscape metrics obtained from a light detection and ranging (LIDAR)-derived digital elevation model (DEM) and compared results to a classification based on field-collected edaphic variables. Our secondary objective was to compare the performance of linear discriminant analysis (LDA) with non-parametric classification and regression trees (CART) for these classifications. Models based on the edaphic variables soil water content, salinity, and redox attained accuracies of 0.62 and 0.71 with LDA and CART, respectively. When the remote sensing-derived variables DEM elevation, slope, distance to the mean high water line, and distance to upland area were used, classification accuracies improved to 0.78 for LDA and 0.79 for CART. Our results suggest that remote sensing-derived metrics can capture edaphic gradients effectively, which makes them especially suited to landscape level analyses of salt marsh plant habitats, with potential application for predicting the effects of sea level rise on salt marsh plant distribution.

Hladik, C.M., Schalles, J.F. and Alber, M. 2013. Salt marsh elevation and habitat mapping using hyperspectral and LIDAR data. Remote Sensing of the Environment. 139:318 - 330. (DOI: 10.1016/j.rse.2013.08.003)

Abstract
Accurate mapping of both elevation and plant distributions in salt marshes is important for management and conservation goals. Although light detection and ranging (LIDAR) is effective at measuring surface elevations, laser penetration is limited in dense salt marsh vegetation. In a previous study, we found that LIDAR-derived digital elevation model (DEM) error varied with vegetation cover. We derived cover-class-specific correction factors to reduce these errors, including separate corrections for three different height classes of Spartina alterniflora, the dominant macrophyte in southeastern U.S. salt marshes. In order to apply these cover class-specific corrections, it is necessary to have information on the distribution of cover classes in a LIDAR-derived DEM. Hyperspectral imagery has been shown to be suitable for the separation of salt marsh vegetation species by spectral signatures, and can be used to determine cover classes; however, there is persistent confusion both among the different height classes of S. alterniflora and between plants and mud (the Spartina problem). This paper presents a method to overcome the respective limitations of LIDAR and hyperspectral imagery through the use of multisensor data. An initial classification of hyperspectral imagery based on the maximum likelihood classification algorithm was used in a decision tree in combination with elevation and normalized difference vegetation index (NDVI) derived from the hyperspectral imagery to map nine salt marsh cover classes. The decision tree appreciably reduced the Spartina problem by reassigning classes using these ancillary data and resulted in a final overall classification accuracy of 90%, with a quantity disagreement of 1% and an allocation disagreement of 9%. The resulting hyperspectral image classification was then used as the basis for applying cover class-specific elevation correction factors to the LIDAR-derived DEM. Applying these correction factors greatly improved the accuracy of the DEM: overall mean error decreased from 0.10 ± 0.12 (SD) to − 0.003 ± 0.10 m, and root mean squared error from 0.15 to 0.10 m. Our results suggest that the use of decision trees to combine elevation and spectral information can aid both hyperspectral image classification and DEM elevation mapping.

Ho, C.-K. and Pennings, S.C. 2008. Consequences of omnivory for trophic interactions on a salt-marsh shrub. Ecology. 89(6):1714-1722. (DOI: 10.1890/07-1069.1)

Abstract
Although omnivory is common in nature, its impact on trophic interactions is variable. Predicting the food web consequences of omnivory is complicated because omnivores can simultaneously produce conflicting direct and indirect effects on the same species or trophic level. We conducted field and laboratory experiments testing the top-down impacts of an omnivorous salt marsh crab, Armases cinereum, on the shrub Iva frutescens and its herbivorous and predatory arthropod fauna. Armases is a ‘‘true omnivore,’’ consuming both Iva and arthropods living on Iva. We hypothesized that Armases would benefit Iva through a top-down trophic cascade, and that this benefit would be stronger than the direct negative effect of Armases on Iva. A field experiment on Sapelo Island, Georgia (USA), supported this hypothesis. Although Armases suppressed predators (spiders), it also suppressed herbivores (aphids), and benefited Iva, increasing leaf number, and reducing the proportion of dead shoots. A one-month laboratory experiment, focusing on the most common species in the food web, also supported this hypothesis. Armases strongly suppressed aphids and consumed fewer Iva leaves if aphids were available as an alternate diet. Armases gained more body mass if they could feed on aphids as well as on Iva. Although Armases had a negative effect on Iva when aphids were not present, Armases benefited Iva if aphids were present, because Armases controlled aphid populations, releasing Iva from herbivory. Although Armases is an omnivore, it produced strong top-down forces and a trophic cascade because it fed preferentially on herbivores rather than plants when both were available. At the same time, the ability of Armases to subsist on a plant diet allows it to persist in the food web when animal food is not available. Because omnivores feed on multiple trophic levels, their effects on food webs may differ from those predicted by standard trophic models that assume that each species feeds only on a single trophic level. To better understand the complexity of real food webs, the variable feeding habits and feeding preferences of different omnivorous species must be taken into consideration.

Ho, C.-K. and Pennings, S.C. 2013. Preference and performance in plant-herbivore interactions across latitude – a study in U.S. Atlantic salt marshes. PLoS One. 8(3). (DOI: 10.1371/journal.pone.0059829)

Abstract
High-latitude plants are often more palatable to herbivores than low-latitude conspecifics. Does increased plant palatability lead to better herbivore performance? Our field and laboratory work investigated (A) whether high-latitude plants have traits indicating that they should be higher-quality foods for herbivores; (B) whether geographic differences in plant quality are more important than local adaptation of herbivores. We studied 3 plant species and 6 invertebrate herbivores in U.S. Atlantic Coast. Past studies had shown high-latitude individuals of these plants are more palatable than low-latitude conspecifics. We documented plant traits and herbivore performance (body size) in the field across latitude. We collected individuals from different latitudes for factorial (plant region x herbivore region) laboratory experiments, examining how herbivore performance was affected by plant region, herbivore region, and their interaction (i.e., local adaptation). Field surveys suggested high-latitude plants were likely of higher quality to herbivores. Leaf nitrogen content in all plant species increased toward high latitudes, consistent with lower leaf C/N and higher leaf chlorophyll content at high latitudes. Furthermore, leaf toughness decreased toward higher latitudes in 1 species. The body size of 4 herbivore species increased with latitude, consistent with high-latitude leaves being of higher quality, while 2 grasshopper species showed the opposite pattern, likely due to life-history constraints. In the laboratory, high-latitude plants supported better performance in 4 herbivore species (marginal in the 5th). The geographic region where herbivores were collected affected herbivore performance in all 6 species; however, the pattern was mixed, indicating a lack of local adaptation by herbivores to plants from their own geographic region. Our results suggest that more-palatable plants at high latitudes support better herbivore growth. Given that geographic origin of either plants or herbivores can affect herbivore performance, the nature of plant-herbivore interactions is likely to change if climate change “reshuffles” plant and herbivore populations across latitude.

Ho, C.-K., Pennings, S.C. and Carefoot, T.H. 2010. Is Diet Quality an Overlooked Mechanism for Bergmann's Rule? The American Naturalist. 175(2):269-276. (DOI: 10.1086/649583)

Abstract
Bergmann's rule (body size increases with latitude) has long interested biologists; however, its mechanism remains unclear. An overlooked mechanism (latitudinal variation in plant quality) might help explain Bergmann's rule. We studied three herbivores. In the field, the planthopper Prokelisia and the sea hare Aplysia, but not the long-horned grasshopper Orchelimum, were larger at high latitudes, following Bergmann's rule. In the laboratory, all three species grew larger or faster on high-latitude plants. High-latitude diets increased Prokelisia size and Aplysia growth rates by 8% and 72%, respectively, enough to explain the increase in field body size toward high latitudes. Therefore, latitudinal variation in herbivore body size could be influenced by latitudinal variation in plant quality, which may directly or indirectly also affect body size in detritivores, parasitoids, and predators. Studies of Bergmann's rule should consider the influence of biotic factors on body size in addition to abiotic factors such as temperature and precipitation.

Holdredge, C., Bertness, M.D., Wettberg, E.V. and Silliman, B.R. 2010. Nutrient enrichment enhances hidden differences in phenotype to drive a cryptic plant invasion. Oikos. 119:1776-1784. (DOI: 10.1111/j.1600-0706.2010.18647.x)

Abstract
Many mechanisms of invasive species success have been elucidated, but those driving cryptic invasions of non-native genotypes remain least understood. In one of the most successful cryptic plant invasions in North America, we investigate the mechanisms underlying the displacement of native Phragmites australis by its Eurasian counterpart. Since invasive Phragmites’ populations have been especially prolific along eutrophic shorelines, we conducted a two-year field experiment involving native and invasive genotypes that manipulated nutrient level and competitor identity (inter- and intra-genotypic competition) to assess their relative importance in driving the loss of native Phragmites. Inter-genotypic competition suppressed above-ground biomass of both native and invasive plants regardless of nutrient treatment (∼ 27%), while nutrient addition disproportionately enhanced the above-ground biomass (by 67%) and lateral expansion (by > 3 × farther) of invasive Phragmites. Excavation of experimental plots indicated that nutrient addition generates these differences in above-ground growth by differentially affecting rhizome production in invasive vs native plants; invasive rhizome biomass and rhizome length increased by 595% and 32% with nutrient addition, respectively, while natives increased by only 278% and 15%. Regardless of nutrient level, native rhizomes produced twice as many roots compared to invasives, which field surveys revealed are heavily infected with mycorrhizal symbionts. These results suggest that native Phragmites competes well under nutrient-limited conditions because its rhizomes are laden with nutrient-harvesting roots and mycorrhizae. Invasive Phragmites’ vigorous above-ground response to nutrients and scarcity of lateral roots, in contrast, may reflect its historic distribution in eutrophic Eurasian wetlands and correspond to its prevalence in New England marshes characterized by elevated nutrient availability and relaxed nutrient competition. These findings reveal that discrete differences in phenotype can interact with anthropogenic modification of environmental conditions to help explain the success of cryptic invaders.

Hollibaugh, J.T., Gifford, S., Moran, M.A., Ross, M., Sharma, S. and Tolar, B. 2014. Seasonal variation in the metratranscriptomes of a Thaumarchaeota population from SE USA coastal waters. ISME Journal. 8:685 - 698. (DOI: 10.1038/ismej.2013.171)

Abstract
We used a combination of metatranscriptomic analyses and quantitative PCR (qPCR) to study seasonal changes in Thaumarchaeota populations from a salt marsh-dominated estuary. Surface waters (0.5 m depth) were sampled quarterly at Marsh Landing, Sapelo Island, GA, USA over a 3-year period. We found a mid-summer peak in Thaumarchaeota abundance measured by qPCR of either 16S rRNA or amoA genes in each of the 3 years. Thaumarchaeota were 100–1000-fold more abundant during the peak than at other times of the year, whereas the abundance of ammonia- and nitrite-oxidizing Bacteria varied <10-fold over the same period. Analysis of the microdiversity of several highly transcribed genes in 20 metatranscriptomes from a 1-year subset of these samples showed that the transcriptionally active population consisted of 2 or 3 dominant phylotypes that differed between successive summers. This shift appeared to have begun during the preceding winter and spring. Transcripts from the same genes dominated the Thaumarchaeota mRNA pool throughout the year, with genes encoding proteins believed to be involved in nitrogen uptake and oxidation, and two hypothetical proteins being the most abundant transcripts in all libraries. Analysis of individual genes over the seasonal cycle suggested that transcription was tied more closely to variation in growth rates than to seasonal changes in environmental conditions. Day–night differences in the relative abundance of transcripts for ribosomal proteins suggested diurnal variation in Thaumarchaeota growth.

Hollibaugh, J.T., Gifford, S., Sharma, S., Bano, N. and Moran, M.A. 2011. Metatranscriptomic analysis of ammonia-oxidizing organisms in an estuarine bacterioplankton assemblage. ISME Journal. 5:866-878. (DOI: 10.1038/ismej.2010.172)

Abstract
Quantitative PCR (qPCR) analysis revealed elevated relative abundance (1.8% of prokaryotes) of marine group 1 Crenarchaeota (MG1C) in two samples of southeastern US coastal bacterioplankton, collected in August 2008, compared with samples collected from the same site at different times (mean 0.026%). We analyzed the MG1C sequences in metatranscriptomes from these samples to gain an insight into the metabolism of MG1C population growing in the environment, and for comparison with ammonia-oxidizing bacteria (AOB) in the same samples. Assemblies revealed low diversity within sequences assigned to most individual MG1C open reading frames (ORFs) and high homology with ‘Candidatus Nitrosopumilus maritimus’ strain SCM1 genome sequences. Reads assigned to ORFs for ammonia uptake and oxidation accounted for 37% of all MG1C transcripts. We did not recover any reads for Nmar_1354–Nmar_1357, proposed to encode components of an alternative, nitroxyl-based ammonia oxidation pathway; however, reads from Nmar_1259 and Nmar_1667, annotated as encoding a multicopper oxidase with homology to nirK, were abundant. Reads assigned to two homologous ORFs (Nmar_1201 and Nmar_1547), annotated as hypothetical proteins were also abundant, suggesting that their unknown function is important to MG1C. Superoxide dismutase and peroxiredoxin-like transcripts were more abundant in the MG1C transcript pool than in the complete metatranscriptome, suggesting an enhanced response to oxidative stress by the MG1C population. qPCR indicated low AOB abundance (0.0010% of prokaryotes), and we found no transcripts related to ammonia oxidation and only one RuBisCO transcript among the transcripts assigned to AOB, suggesting they were not responding to the same environmental cues as the MG1C population.

Hopkinson, C.S., Cai, W.-J. and Hu, X. 2012. Carbon sequestration in wetland dominated coastal systems — aglobal sink of rapidly diminishing magnitude. Current Opinions in Environmental Sustainability. 4:186 - 194. (DOI: 10.1016/j.cosust.2012.03.005)

Abstract
Coastal vegetated wetlands have recently been identified asvery important global C sinks but vulnerable to degradation bydirect human alteration of their habitats. While their expanse issmall globally, areal rates of C burial, or sequestration, areamong the highest of Earth’s ecosystems. There isconsiderable uncertainty in the magnitude of total globalsequestration in these systems for two reasons: poor estimatesof their global areas and high variability and uncertainty in arealrates of burial between systems. The magnitude of C burial invegetated coastal systems has been decreasing rapidly overthe past century due primarily to human disturbances such asdredging, filling, eutrophication, and timber harvest. Thesesystems continue to be lost globally at rates ranging from 1% to7% annually. We find that climate change including globalwarming, human engineering of river systems, continuedagricultural expansion, and sea level rise will also negativelyimpact C burial of coastal vegetated wetlands. A decrease inglobal C burial in these systems will ultimately exacerbate CO2emissions, and further contribute to climate change in thefuture.

Hopkinson, C.S., Lugo, A., Alber, M., Covich, A. and Van Bloem, S.J. 2008. Understanding and forecasting the effects of sea level rise and intense windstorms on coastal and upland ecosystems: the need for a continental-scale network of observatories. Frontiers in Ecology. 6(5):255-263. (DOI: 10.1890/070153)

Abstract
We identify a continental-scale network of sites to evaluate how two aspects of climate change – sea-level rise and intensification of windstorms – will influence the structure, function, and capacity of coastal and inland forest ecosystems to deliver ecosystem services (eg carbon sequestration, storm protection, pollution control, habitat support, food). The network consists of coastal wetland and inland forest sites across the US and is representative of continental-level gradients of precipitation, temperature, vegetation, frequency of occurrence of major windstorms, value of insured properties, tidal range, watershed land use, and sediment availability. The network would provide real-time measurements of the characteristics of sea-level rise and windstorm events and would allow an assessment of the responses of wetlands, streams, and inland forests at spatial and temporal scales associated with sustainability of ecosystem services. We illustrate the potential of this approach with examples of hypotheses that could be tested across the network.

Huang, H., Chen, C., Blanton, J.O. and Andrade, F. 2008. A numerical study of tidal asymmetry in Okatee Creek, South Carolina. Estuarine Coastal and Shelf Science. 78:190-202. (DOI: 10.1016/j.ecss.2007.11.027)

Abstract
The Okatee River, South Carolina is characterized by a narrow tidal channel and an extensive area of intertidal salt marshes. Current measurements in the upstream portion Okatee Creek show that tidal flow features an asymmetric pattern: ebb current is stronger than flood current. The ebb dominance is mainly caused by deformation of the dominant astronomical tidal constituent M2. An unstructured grid, finite volume coastal ocean model (FVCOM) with wet-dry point treatment method is applied to examine physical mechanisms of M4 overtide generation. Model experiments show that mean absolute amplitude and phase errors are 3.1 cm and 1.7 for M2 elevation, 2.4 cm s-1 and 0.8 for M2 current major axis, 2.1 cm and 1.8 for M4 elevation, and 2.1 cm s-1 and 24.6 for M4 current major axis. The overall pattern of tidal asymmetry is qualitatively reproduced. Various sensitivity experiments suggest that the generation of M4 overtide is a result of nonlinear interaction of tidal currents with irregular creek geometry and bottom topography. Consistent with the classical view, the large volume of intertidal water storage is the major reason for ebb dominance in the creek. However, the zero-inertia assumption (i.e., negligible advective terms) is probably not valid for the entire tidal cycle. Besides the pressure gradient force and the bottom friction force, terms related to lateral shear of the along-estuary velocity (i.e., advective inertia and horizontal eddy viscosity) may also contribute in horizontal momentum balance. Exclusion of the flooding-draining processes over the intertidal zone will severely underestimate tidal currents in the river channel and make the tidal asymmetry less prominent. Published by Elsevier Ltd.

Hübner, L., Pennings, S.C. and Zimmer, M. 2015. Sex- and habitat-specific movement of an omnivorous semi-terrestrial crab controls habitat connectivity and subsidies: A multi-parameter approach. Oecologia. 3/2015:17. (DOI: 10.1007/s00442-015-3271-0)

Abstract
Distinct habitats are often linked through fluxes of matter and migration of organisms. In particular, intertidal ecotones are prone to being influenced from both the marine and the terrestrial realms, but whether or not small-scale migration for feeding, sheltering or reproducing is detectable may depend on the parameter studied. Within the ecotone of an upper saltmarsh in the United States, we investigated the sex-specific movement of the semi-terrestrial crab Armases cinereum using an approach of determining multiple measures of across-ecotone migration. To this end, we determined food preference, digestive abilities (enzyme activities), bacterial hindgut communities (genetic fingerprint), and the trophic position of Armases and potential food sources (stable isotopes) of males versus females of different sub-habitats, namely high saltmarsh and coastal forest. Daily observations showed that Armases moved frequently between high-intertidal (saltmarsh) and terrestrial (forest) habitats. Males were encountered more often in the forest habitat, whilst gravid females tended to be more abundant in the marsh habitat but moved more frequently. Food preference was driven by both sex and habitat. The needlerush Juncus was preferred over three other high-marsh detrital food sources, and the periwinkle Littoraria was the preferred prey of male (but not female) crabs from the forest habitats; both male and female crabs from marsh habitat preferred the fiddler crab Uca over three other prey items. In the field, the major food sources were clearly vegetal, but males have a higher trophic position than females. In contrast to food preference, isotope data excluded Uca and Littoraria as major food sources, except for males from the forest, and suggested that Armases consumes a mix of C4 and C3 plants along with animal prey. Digestive enzyme activities differed significantly between sexes and habitats and were higher in females and in marsh crabs. The bacterial hindgut community differed significantly between sexes, but habitat effects were greater than sex effects. By combining multiple measures of feeding ecology, we demonstrate that Armases exhibits sex-specific habitat choice and food preference. By using both coastal forest and saltmarsh habitats, but feeding predominantly in the latter, they possibly act as a key biotic vector of spatial subsidies across habitat borders. The degree of contributing to fluxes of matter, nutrients and energy, however, depends on their sex, indicating that changes in population structure would likely have profound effects on ecosystem connectivity and functioning.

Hunter, E., Nibbelink, N., Alexander, C.R. Jr., Barrett, K., Mengak, L., Guy, R., Moore, C. and Cooper, R. 2015. Coastal vertebrate exposure to predicted habitat changes due to sea level rise. Environmental Management. (DOI: 10.1007/s00267-015-0580-3)

Abstract
Sea level rise (SLR) may degrade habitat for coastal vertebrates in the Southeastern United States, but it is unclear which groups or species will be most exposed to habitat changes. We assessed 28 coastal Georgia vertebrate species for their exposure to potential habitat changes due to SLR using output from the Sea Level Affecting Marshes Model and information on the species’ fundamental niches. We assessed forecasted habitat change up to the year 2100 using three structural habitat metrics: total area, patch size, and habitat permanence. Almost all of the species (n = 24) experienced negative habitat changes due to SLR as measured by at least one of the metrics. Salt marsh and ocean beach habitats experienced the most change (out of 16 categorical land cover types) across the three metrics and species that used salt marsh extensively (rails and marsh sparrows) were ranked highest for exposure to habitat changes. Species that nested on ocean beaches (Diamondback Terrapins, shorebirds, and terns) were also ranked highly, but their use of other foraging habitatsreduced their overall exposure. Future studies on potential effects of SLR on vertebrates in southeastern coastal ecosystems should focus on the relative importance of different habitat types to these species’ foraging and nesting requirements. Our straightforward prioritization approach is applicable to other coastal systems and can provide insight to managers on which species to focusresources, what components of their habitats need to be protected, and which locations in the study area will provide habitat refuges in the face of SLR.

Jiang, L., Cai, W.-J. and Wang, Y. 2008. A comparative study of carbon dioxide degassing in river- and marine-dominated estuaries. Limnology and Oceanography. 53(6):2603-2615.

Abstract
The partial pressure of carbon dioxide (pCO2), concentration of total dissolved inorganic carbon (DIC) and total alkalinity (TA) were measured at both high tide and low tide in the surface water of three Georgia (United States of America) estuaries from September 2002 to May 2004. Of the three estuaries, Sapelo and Doboy Sounds are marine-dominated estuaries, while Altamaha Sound is a river-dominated estuary. During all sampling months, the three estuaries were supersaturated in CO2 with respect to the atmosphere (39.5-342.5 Pa, or 390 - 3380 µatm) due to CO2 inputs from within the estuarine zone (mainly intertidal marshes) and the river. Overall, pCO2 in the river-dominated estuary is much higher than that in the marine-dominated estuaries. The calculated annual air-water CO2 flux in Altamaha Sound (69.3 mmol m-2 d-1) is 2.4 times those of Sapelo and Doboy Sounds (28.7-29.4 mmol m-2 d-1). The higher CO2 degassing in the river-dominated estuary is largely fueled by CO2 loading from the river. Because of the substantial differences between river- and marine-dominated estuaries, current estimates of air-water CO2 fluxes in global estuaries (which are based almost entirely on river-dominated estuaries) could be overestimated.

Jiang, L., Cai, W.-J., Feely, R.A., Wang, Y., Guo, X., Gledhill, D.K., Hu, X., Arzayus, F., Chen, F., Hartmann, J. and Zhang, L. 2010. Carbonate mineral saturation states along the U.S. east coast. Limnology and Oceanography. 55(6):2424–2432. (DOI: 10.4319/lo.2010.55.6.2424)

Abstract
To assess the impact of ocean acidification on the carbonate chemistry of the shelf waters off the southeastern United States (South Atlantic Bight [SAB]), we measured carbonate mineral saturation states from January 2005 to May 2006. The findings reveal that aragonite (Varag: 2.6–4.0) and calcite (Vcal: 4.1–6.0) saturation states were considerably higher than those recently reported along the West Coast of North America. Different water mass age between the Atlantic and Pacific Oceans during global ocean circulation is the primary reason for the higher carbonate mineral saturation states in the SAB than along the West Coast. The contrasting water temperatures in the two coasts contribute to such differences. Both upwelling and freshwater discharge also play important roles in controlling saturation state. Carbonate mineral saturation in the surface water of the West Coast is strongly controlled by the upwelling of high-salinity, low-temperature, low-oxygen, and low-pH deep water. In comparison, saturation states in the surface water of the SAB coast are rarely affected by upwelling. Instead, they are strongly influenced by the input of low-saturation-state water from rivers. Continued increases of atmospheric CO2 under the Intergovernmental Panel on Climate Change B1 emission scenario will decrease the carbonate mineral saturation states by up to 40% by the end of this century, and aragonite will approach undersaturation near the coast.

Jiang, L., Cai, W.-J., Wang, Y. and Bauer, J. 2013. Influence of terrestrial inputs on continental shelf carbon dioxide. Biogeosciences. 10:839 - 849. (DOI: 10.5194/bg-10-839-2013)

Abstract
The US South Atlantic Bight (SAB) is a low-latitude shallow continental shelf bordered landward by abundant salt marshes and rivers. Based on previously published data on sea surface partial pressure of carbon dioxide (pCO2) and new dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) data, a model analysis is presented to identify and quantify the contributions of various terrestrial carbon inputs on SAB sea surface pCO2. After removal of pCO2 variations due to annual temperature variability and air–sea gas exchange from the in situ pCO2, the temperature- and gas-exchange-corrected pCO2 (TG-corrected pCO2) is derived. Contributions from rivers, salt marshes, and the continental shelf to the TG-corrected pCO2 are then calculated. Our findings demonstrate that although additions of CO2 from within shelf waters (i.e., ΔpCO2(shelf)) were the greatest of the three components and underwent the largest seasonal changes, ΔpCO2(shelf) showed smaller onshore–offshore gradients than rivers and marshes. In contrast, CO2 contributions from river (ΔpCO2(river)) and salt marsh (ΔpCO2(marsh)) components were greatest closest to the coast and decreased with distance offshore. In addition, the magnitude of ΔpCO2(marsh) was about three-fold greater than ΔpCO2(river). Our findings also revealed that decomposition of terrestrial organic carbon was an important factor regulating the seasonal pattern of pCO2 on the inner shelf. Despite large uncertainties, this study demonstrates the importance of terrestrial inputs, in particular those from coastal wetlands, on coastal ocean CO2 distributions.

Jiang, L., Cai, W.-J., Wang, Y., Diaz, J., Yager, P. and Hu, X. 2010. Pelagic community respiration on the continental shelf off Georgia, USA. Biogeochemistry. 98:101–113. (DOI: 10.1007/s10533-009-9379-8)

Abstract
The South Atlantic Bight (SAB) has been a focus for the study of continental shelf ecosystem respiration during the past two decades. However, two questions concerning respiration in this area have yet to be answered. First, why do previous estimates of respiration in the SAB exceed measured carbon fixation rates by almost an order of magnitude? Second, considering that bacteria are responsible for most of the pelagic community respiration in the SAB, why is respiration almost uniform from the coastline to the shelf break, while bacterial production estimates decrease offshore? This study addresses these critical questions by presenting new pelagic community respiration data that were collected across the entire width of the continental shelf off Georgia, USA from June 2003 to May 2006. The respiration was calculated as in vitro changes of dissolved oxygen and dissolved inorganic carbon concentrations during deck incubations. The measured respiration rates ranged from 0.3(±0.1) to 21.2(±1.4) mmol m−3 day−1. They followed a clear seasonal pattern, being lowest over the entire shelf in winter and reaching maxima in summer. Summertime respiration rates were highest on the inner shelf and decreased with distance offshore. Consistent with this trend, bacterial abundance measurements taken during the sampling month of July 2005 followed a pattern of seaward decline. The SAB organic carbon fluxes calculated from the respiration data are close to the estimates for primary production, which resolves a long-standing mystery regarding perceived carbon imbalance in the SAB.

Jiang, L., Cai, W.-J., Wang, Y., Wanninkhof, R. and Luger, H. 2008. Air-sea CO2 fluxes on the US South Atlantic Bight: Spatial and temporal variability. Journal of Geophysical Research-Ocean. 113:C07019. (DOI: 10.1029/2007JC004366)

Abstract
The partial pressure of carbon dioxide (pCO2) in surface seawater on the South Atlantic Bight (SAB) of the United States was measured during six cruises from January 2005 to May 2006. The high-resolution pCO2 data allow us to create the first maps of the sea surface pCO2 over the SAB for all seasons. Contrary to an earlier study that was based on limited spatial and seasonal coverage, this study shows that the SAB is a net sink of atmospheric CO2 on an annual basis (-0.48 ± 0.21 mol m-2 a-1). The inner shelf is a source of +1.20 ± 0.24 mol m-2 a-1, while the middle and outer shelves are sinks of -1.23 ± 0.19 and -1.37 ± 0.21 mol m-2 a-1, respectively. Seasonally, the SAB shifts from a sink for atmospheric CO2 in winter to a source in summer. The annual cycle of sea surface temperature plays a dominant role in controlling the seasonal variation of the pCO2. Wind speeds are seasonally anti-correlated with the air-sea pCO2 differences, and this is an important factor in contributing to the net annual air-sea CO2 exchange. Factors related to the estimates of CO2 fluxes in the coast ocean, such as the choice of wind speeds, the correction of gas transfer equations with nonlinearity coefficients, the effect of diel variations of pCO2, the spatial extrapolation of the pCO2 to the nearshore area, and the seasonal interpolation are also discussed.

Jimenez, J.M., Wieski, K., Marczak, L., Ho, C.-K. and Pennings, S.C. 2012. Effects of an omnivorous katydid, salinity, and nutrients on a planthopper-Spartina food web. Estuaries and Coasts. 35:475-485. (DOI: 10.1007/s12237-011-9458-7)

Abstract
Top–down and bottom–up effects interact tostructure communities, especially in salt marshes, whichcontain strong gradients in bottom–up drivers such assalinity and nutrients. How omnivorous consumers respondto variation in prey availability and plant quality is poorlyunderstood. We used a mesocosm experiment to examinehow salinity, nutrients, an omnivore (the katydid Orchelimumfidicinium) and an herbivore (the planthopper Prokelisiaspp.) interacted to structure a simplified salt marsh food webbased on the marsh grass Spartina alterniflora. Bottom–upeffects were strong, with both salinity and nutrientsdecreasing leaf C/N and increasing Prokelisia abundance.Top–down effects on plants were also strong, with both theherbivore and the omnivore affecting S. alterniflora traitsand growth, especially when nutrients or salt were added. Incontrast, top–down control by Orchelimum of Prokelisia wasindependent of bottom–up conditions. Orchelimum grewbest on a diet containing both Spartina and Prokelisia, and incontrast to a sympatric omnivorous crab, did not shift to ananimal-based diet when prey were present, suggesting that itis constrained to consume a mixed diet. These results suggestthat the trophic effects of omnivores depend on omnivorebehavior, dietary constraints, and ability to suppress lowertrophic levels, and that omnivorous katydids may play apreviously unrecognized role in salt marsh food webs.

Jun, M.h., Altor, A. and Craft, C.B. 2013. Effects of Increased Salinity and Inundation on Inorganic N and P Exchange by Tidal Freshwater Floodplain Forest Soils, Georgia (USA). Estuaries and Coasts. 36:508-518. (DOI: 10.1007/s12237-012-9449-6)

Abstract
We investigated the effects of increasing salinity and inundation on inorganic N exchange and P sorption/precipitation in soils of tidal freshwater floodplain forests (TFFF) of coastal Georgia, USA. Our objectives were to better understand how sea level rise, increasing inundation, and saltwater intrusion will affect the ability of TFFFs to retain nitrogen (N) and phosphorus (P). We collected soil cores (0–5 cm) from three TFFFs that do not currently experience saltwater intrusion and from one TFFF currently experiencing saltwater intrusion and measured NH4-N exchange and PO4-P removal over five simulated 6-h tidal cycles using nutrient-enriched freshwater (30 µM NH4-N and 5 µM PO4-P). In a second experiment, we exposed soil cores to three salinities (0, 2, and 5) and two inundation depths (5 and 10 cm) using the same nutrient enrichment. When flooded with nutrient-enriched freshwater, soils from the three TFFFs that do not experience saltwater intrusion removed inorganic N and P in amounts ranging from 5.2 to 10.7 and 2.3 to 4.4 mg/m2, respectively, and the TFFF soils experiencing saltwater intrusion removed 2.1 to 3.8 mg P/m2. However, TFFF soils experiencing saltwater intrusion released inorganic N to the water column in amounts ranging from 7.1 to 67.5 mg/m2. In the second experiment, soils from TFFFs not experiencing saltwater intrusion released NH4-N to the water column when exposed to 2 and 5 salinity, and the amount of N released increased with salinity and number of tidal cycles. In contrast, the same TFFF soils sorbed two and three times more PO4-P when exposed to 2 and 5 salinity than when exposed to 0 salinity. P removal on a mass basis was greater under 10 cm of inundation, but the efficiency of removal was greater under the 5 cm flooding depth. Our findings suggest that saltwater intrusion caused by sea level rise will promote N release into the water column through organic matter mineralization and/or ion exchange and may promote P sorption, or precipitation of P with metal cations. In addition, release of N and resulting increased N/P could exacerbate eutrophication of estuaries in the future.

Jung, Y. and Burd, A.B. 2017. Seasonal changes in above- and below-ground non-structural carbohydrates (NSC) in Spartina alterniflora in a marsh in Georgia, USA. Aquatic Botany. 140:13-22. (DOI: https://doi.org/10.1016/j.aquabot.2017.04.003)

Abstract
Spartina alterniflora is the dominant grass appearing in salt marshes along the east coast of the USA. The development of predictive, mechanistic models of Spartina has been hindered by the lack of information on below-ground biomass and its dynamics, and in particular the storage of resources that can be used for spring re-growth. We studied the dynamics of non-structural carbohydrates (glucose, fructose, sucrose, and starch) and biomass in 8 different above- and below-ground tissues in S. alterniflora over the course of a year in a salt marsh on Sapelo Island, Georgia, USA. We found greater seasonal variability in non-structural carbohydrates in S. alterniflora than had been previously reported, with concentrations varying between 3.3% through 17.3% of the total biomass and between 0% and 19.5% of dry weight depending on the type of tissue, with statistical differences between the different tissues. We found that sucrose was the dominant non-structural carbohydrate in above- and below-ground tissue, and that this sugar was likely used for long-term storage during winter months and as a resource for early spring growth. Glucose, fructose, and starch showed less variability, with glucose following changes in above-ground biomass more closely indicating their use as short-term storage. We were unable to develop a coherent carbon budget for the plants largely because of uncertainties in modeled net primary production and heterogeneity in below-ground biomass.

Kang, K. and Di Iiorio, D. 2005. Depth- and current-induced effects on wave propagation into the Altamaha River Estuary, Georgia. Estuarine, Coastal and Shelf Science. 66:395-408.

Abstract
A study of sea surface wave propagation and its energy deformation was carried out using field observations and numerical experiments over a region spanning the midshelf of the South Atlantic Bight (SAB) to the Altamaha River Estuary, GA. Wave heights on the shelf region correlate with the wind observations and directional observations show that most of the wave energy is incident from the easterly direction. Comparing mid-shelf and inner-shelf wave heights during a time when there was no wind and hence no wave development led to an estimation of wave energy dissipation due to bottom friction with corresponding wave dissipation factor of 0.07 for the gently sloping continental shelf of the SAB. After interacting with the shoaling region of the Altamaha River, the wave energy within the estuary becomes periodic in time showing wave energy during flood to high water phase of the tide and very little wave energy during ebb to low water. This periodic modulation inside the estuary is a direct result of enhanced depth and current-induced wave breaking that occurs at the ebb shoaling region surrounding the Altamaha River mouth at longitude 81.23W. Modelling results with STWAVE showed that depth-induced wave breaking is more important during the low water phase of the tide than current-induced wave breaking during the ebb phase of the tide. During the flood to high water phase of the tide, wave energy propagates into the estuary. Measurements of the significant wave height within the estuary showed a maximum wave height difference of 0.4 m between the slack high water (SHW) and slack low water (SLW). In this shallow environment these wave-current interactions lead to an apparent bottom roughness that is increased from typical hydraulic roughness values, leading to an enhanced bottom friction coefficient.

Kang, K. and Di Iorio, D. 2008. A study of estuarine flow using the roving adcp data. Ocean Science Journal. 43(2):81-90. (DOI: 10.1007/BF03020584)

Abstract
A study of estuarine flows during a neap tide was performed using 13-hour roving acoustic Doppler current profiles (ADCP) and conductivity-temperature-depth (CTD) profiles in the Altamaha River estuary, Georgia, U.S.A. The least-squared harmonic analysis method was used to fit the tidal (M2) component and separate the flow into two components: the tidal and residual (M2-removed) flows. We applied this method to depth-averaged data. Results show that the M2 component demonstrates over 95% of the variability of observation data. As the flow was dominated by the M2 tidal component in a narrow channel, the tidal ellipse distribution was essentially a back-and-forth motion. The amplitude of M2 velocity component increased slightly from the river mouth (0.45 m/sec) to land (0.6 m/sec) and the phase showed fairly constant values in the center of the channel and rapidly decreasing values near the northern and southern shoaling areas. The residual flow and transport calculated from depth-averaged flow shows temporal variability over the tidal time scale. Strong landward flows appeared during slack waters which may be attributed to increased baroclinic forcing when turbulent mixing decreases.

Ket, W., Schubauer-berigan, J. and Craft, C.B. 2011. Effects of five years of nitrogen and phosphorus additions on a Zizaniopsis miliacea tidal freshwater marsh. Aquatic Botany. 95:17-23. (DOI: 10.1016/j.aquabot.2011.03.003)

Abstract
The purpose of this experiment was to determine if nitrogen (N) or phosphorus (P) acts as the limiting nutrient for tidal freshwater marsh vegetation. To answer this question, we added N, P, and N + P to a tidal freshwater marsh dominated by Zizaniopsis miliacea (Michx.) (giant cutgrass) in Georgia, USA, for five years to determine their effects on aboveground and belowground biomass and nutrient (N, P) uptake. Nitrogen and P were applied twice per year at an annual rate of 50 g m−2 year−1 and 10 g m−2 year−1, respectively. Aboveground biomass and leaf C, N, and P were sampled in August of each year. Belowground biomass and C, N, and P content were measured in August of year five. After two years, plots receiving N and N + P had significantly greater aboveground biomass than the control and P plots. This trend continued through the fifth year of the study and resulted in two to three times more aboveground biomass at the end of the fifth year in the N (1570 g m−2) and N + P (1264 g m−2) plots relative to P (710 g m−2) and control (570 g m−2) plots. After five years of nutrient additions, macro-organic matter (MOM), the living plus dead root and rhizome mat (0–10 cm), was significantly lower in the N(1457 g m−2) and N + P (994 g m−2) plots than the control (2189 g m−2) plots. There was less live rhizome biomass in the N + P (23 g m−2) plots than the control (1085 g m−2) plots. We observed a 31–33% increase in the N content of Z. miliacea leaves in years three through five in the N and N + P plots relative to the control plots, but observed no P enrichment of leaves. In the N-treated plots, leaf C:N decreased 20–25% whereas N:P increased 21–64% in years three through five relative to the control and P plots. These findings collectively suggest that N, rather than P, limits productivity of tidal freshwater marsh vegetation. Reduced belowground biomass that accompanies N enrichment is of special concern as it may lead to increased erosion and reduced organic matter inputs to the soil, increasing their susceptibility to disturbances associated with wind, waves, river flooding and rising sea level.

Kinney, K.A., Pintor, L.M. and Byers, J. 2019. Does predator-driven, biotic resistance limit the northward spread of the non-native green porcelain crab, Petrolisthes armatus? Biological Invasions. 21:245-260. (DOI: 10.1007/s10530-018-1821-1)

Abstract
Biotic resistance by native predators can limit the geographic range and abundance of nonnative species following introduction into an ecosystem. Here we tested the hypothesis that the strength ofpredation pressure varies with latitude and limits the abundance and northward expansion of the non-native green porcelain crab, Petrolisthes armatus, whose northern range is also hypothesized to be limited by physical tolerances to cold temperatures. We quantified the predation risk of P. armatus across 400 km of the crab’s invasive range along the coastline of the southeastern US. In addition, we measured the density of large P. armatus, habitat quality, and other environmental factors that may affect the crab’s predation risk. Finally, we conducted a size-selective predator exclusion experiment to determine the predator species and size classes that may be consuming P. armatus. Results indicated that neither the density of large P. armatus nor its predation risk varied systematically with latitude. Instead, variation in predation risk was best explained by local site-level differences in habitat quality, the density of large P. armatus, and the mean abundance of predators. The predator exclusion experiment indicated that both small and large size classes of predators are capable of equallystrong rates of predation on P. armatus. Together, our results suggest that although native predators readily consume P. armatus, they do not provide biotic resistance against its northward expansion. Instead, it seems likely that other latitudinally differential factors like low winter temperatures that decrease P. armatus survival are more influential in limiting the crab’s northern expansion.

Koch, E.W., Barbier, E.B., Silliman, B.R., Reed, D.J., Perillo, M.E., Hacker, S.D., Granek, E.F., Primavera, J.H., Muthiga, N., Polasky, S., Halpern, B.S., Kennedy, C.J., Kappel, C.V. and Wolanski, E. 2009. Non-linearity in ecosystem services: temporal and spatial variability in coastal protection. Frontiers in Ecology and the Environment. 7(1):29-37. (DOI: 10.1890/080126)

Abstract
Natural processes tend to vary over time and space, as well as between species. The ecosystem services these natural processes provide are therefore also highly variable. It is often assumed that ecosystem services are provided linearly (unvaryingly, at a steady rate), but natural processes are characterized by thresholds and limiting functions. In this paper, we describe the variability observed in wave attenuation provided by marshes, mangroves, seagrasses, and coral reefs and therefore also in coastal protection. We calculate the economic consequences of assuming coastal protection to be linear. We suggest that, in order to refine ecosystem-based management practices, it is essential that natural variability and cumulative effects be considered in the valuation of ecosystem services

Krull, K. and Craft, C.B. 2009. Ecosystem development of a sandbar emergent tidal marsh, Altamaha River estuary, Georgia USA. Wetlands. 29(1):314-322. (DOI: 10.1672/06-178.1)

Abstract
Vegetation structure and soil properties were measured on a sandbar, a three year old sandbar emergent marsh (SEM), and five mature Spartina alterniflora Loisel marshes located near the mouth of the Altamaha River (Georgia, USA) to determine how quickly tidal marsh vegetation and soils develop during primary succession. Those data were compared to published data collected from young (10–16 yr old) natural marshes in Virginia and young (1–28 yr old) constructed marshes in North Carolina to determine if the rate of ecosystem development is similar among tidal marshes of the southeastern US coast. Within three years of emergence, aboveground biomass of SEM was comparable to mature marshes in the area, although stem height and density were distinctly different as the SEM contained more stems that were of shorter height than mature marshes. Following colonization by vegetation, soil properties (0–30 cm) of SEM had begun to differentiate from sediments of the sandbar. Surface (0–10 cm) and subsurface (10–30 cm) soil bulk density was less, and organic carbon (C), nitrogen (N), and percent silt (0–10 cm) were greater in sediments of SEM than in the sandbar. Even so, soils of SEM contained less organic C, N, silt, and clay than mature marshes. However, accumulation rates of organic C (260 ± 40 g m-2 yr-1) and N (11 ± 3 g m-2 yr-1) in soils of SEM was 5 to 7 times greater than in mature marshes (35 ± 4 g C m-2 yr-1, 2 ± 0.2 g N m-2 yr-1). Trajectories of development for soil organic C and N pools were similar for our SEM, young natural S. alterniflora marshes in Virginia, and young constructed S. alterniflora marshes in North Carolina suggesting that tidal marsh soil development proceeds at similar rates for tidal marshes along much of the southeast US coast.

Kunza, A.E. and Pennings, S.C. 2008. Patterns of plant diversity in Georgia and Texas salt marshes. Estuaries and Coasts. 31:673-681.

Abstract
A fundamental question in ecology is how biological interactions and biogeographic processes interact to determine the biodiversity of local sites. We quantified patterns of plant species diversity on transects across elevation at 59 salt marsh sites in Georgia and 49 sites in Texas. Although these regions have similar climates and floras, we anticipated that diversity might differ because of differences in tidal regime. Diversity was measured at global, regional, site, and plot scales to consider processes occurring at all levels. Species pools were similar between regions. Texas had greater diversity at the site and plot scales, suggesting that processes occurring at the site scale differed. The greater diversity of Texas sites and plots was associated with wider distributions of individual species across the marsh landscape, and proportionally more middle marsh (a high diversity zone) and less low marsh (a low diversity zone) than in Georgia marshes. Preliminary data suggested that these differences were not due to differences in salinity regime or standing biomass between regions, leaving differences in tidal regime as the most plausible hypothesis accounting for differences in plant diversity. We speculate that the less-predictable tidal regime in Texas leads to temporal variation in abiotic conditions that limit the ability of any one species to competitively exclude others from particular marsh zones.

Lasher, C., Dyszynski, G., Everett, K., Ye, W., Sheldon, W.M. Jr., Joye, S.B., Moran, M.A. and Whitman, W.B. 2009. The diverse bacterial community in intertidal, anaerobic sediments at Sapelo Island, Georgia. Microbial Ecology. 58(2):244-261. (DOI: 10.1007/s00248-008-9481-9)

Abstract
The phylogenetic diversity and composition of the bacterial community in anaerobic sediments from Sapelo Island, GA, USA were examined using 16S rRNA gene libraries. The diversity of this community was comparable to that of soil, and 1,186 clones formed 817 OTUs at 99% sequence similarity. Chao1 estimators for the total richness were also high, at 3,290 OTUs at 99% sequence similarity. The program RDPquery was developed to assign clones to taxonomic groups based upon comparisons to the RDP database. While most clones could be assigned to describe phyla, fewer than 30% of the clones could be assigned to a described order. Similarly, nearly 25% of the clones were only distantly related (<90% sequence similarity) to other environmental clones, illustrating the unique composition of this community. One quarter of the clones were related to one or more undescribed orders within the γ-Proteobacteria. Other abundant groups included the δ-Proteobacteria, Bacteroidetes, and Cyanobacteria. While these phyla were abundant in other estuarine sediments, the specific members at Sapelo Island appeared to be different from those previously described in other locations, suggesting that great diversity exists between as well as within estuarine intertidal sediments. In spite of the large differences in pore water chemistry with season and depth, differences in the bacterial community were modest over the temporal and spatial scales examined and generally restricted to only certain taxa.

Letourneau, M.L. and Medeiros, P.M. 2019. Dissolved organic matter composition in a marsh-dominated estuary: Response to seasonal forcing and to the passage of a hurricane. Journal of Geophysical Research: Biogeosciences. 124:1545-1559. (DOI: 10.1029/2018JG004982)

Abstract
Dissolved organic matter (DOM) is a large and complex mixture of compounds with source inputs that differ with location, season and environmental conditions. Here, we investigated drivers of DOM composition changes in a marsh-dominated estuary off the southeastern U.S. Monthly water samples were collected at a riverine and estuarine site from September 2015 to September 2016, and bulk, optical, and molecular analyses were conducted on samples before and after dark incubations. Results showed that river discharge was the primary driver changing the DOM composition at the mouth of the Altamaha River. For discharge higher than ~ 150 m3 s-1, DOC concentrations and the terrigenous character of the DOM increased approximately linearly with river flow. For low discharge conditions, a clear signature of salt marsh-derived compounds was observed in the river. At the head of Sapelo Sound, changes in DOM composition were primarily driven by river discharge and possibly by summer algae blooms. Microbial consumption of DOC was larger during periods of high discharge at both sites, potentially due to the higher mobilization and influx of fresh material to the system. The Georgia coast was hit by Hurricane Matthew in October 2016, which resulted in a large input of carbon to the estuary. The DOC concentration was ~ 2 times higher and DOM composition was more aromatic with a stronger terrigenous signature compared to the seasonal maximum observed earlier in the year during peak river discharge conditions. This suggests that extreme events notably impact DOM quantity and quality in estuarine regions.

Li, F. and Pennings, S.C. 2018. Responses of tidal freshwater and brackish marsh macrophytes to pulses of saline water simulating sea level rise and reduced discharge. Wetlands. 38:885-891. (DOI: 10.1007/s13157-018-1037-2)

Abstract
Coastal low-salinity marshes are increasingly experiencing periodic to extended periods of elevated salinities due to the combined effects of sea level rise and altered hydrological and climatic conditions. However, we lack the ability to predict detailed vegetation responses, especially for saline pulses that are more realistic in nature than permanent saline presses. In this study, we exposed common freshwater and brackish plants to different durations (1–31 days per month for 3 months) of saline water (salinity of 5).We found that Zizaniopsis miliacea was more tolerant to salinity than the other two freshwater species, Polygonum hydropiperoides and Pontederia cordata. We also found that Zizaniopsis miliacea belowground and total biomass appeared to increase with salinity pulses up to 16 days in length, although this relationship was quite variable. Brackish plants, Spartina cynosuroides, Schoenoplectus americanus and Juncus roemerianus, were unaffected by the experimental treatments. Our experiment did not evaluate how competitive interactions would further affect responses to salinity but our results suggest thehypothesis that short pulses of saline water will increase the cover of Zizaniopsis miliacea and decrease the cover of Polygonum hydropiperoides and Pontederia cordata in tidal freshwater marshes, thereby reducing diversity without necessarily affecting total plant biomass.

Li, F. and Pennings, S.C. 2019. Response and Recovery of Low-Salinity Marsh Plant Communities to Presses and Pulses of Elevated Salinity. Estuaries and Coasts. 42:708-718. (DOI: 10.1007/s12237-018-00490-1)

Abstract
In estuaries, future variation in sea level and river discharge will lead to saline intrusion into low-salinity tidal marshes. Toinvestigate the processes that control the differential response and recovery of tidal freshwater marsh plant communities to salinepulses, a 3 × 5 factorial greenhouse experiment was conducted to examine the effects of a range of salinity levels (3, 5, and10 practical salinity units (PSU)) and pulse durations (5, 10, 15, 20, and 30 days per month) on community composition of tidalfreshwater marsh vegetation. Recovery of perturbed communities was also examined after 10 months. The results showed thatcommunity composition was increasingly affected by the more-saline and longer-duration treatments. The increasing suppressionof salt-sensitive species resulted in species reordering, decreased species richness, and decreased aboveground biomass. Most ofthe plant species were able to recover from low-salinity, short-duration saline pulses in less than 1 year. However, because not allspecies recovered in the heavily salinized treatments, species richness at the end of the recovery period remained low fortreatments that were heavily salinized during the treatment period. In contrast, plant aboveground biomass fully recovered inthe heavily salinized treatments. Although the magnitude and duration of pulsed environmental changes had strong effects oncommunity composition, shifts in community composition prevented long-term reductions in productivity. Thus, in this studysystem, environmental change affected species composition more strongly than it did ecosystem processes.

Li, S. and Pennings, S.C. 2016. Disturbance in Georgia salt marshes: variation across space and time. Ecosphere. 7(10):e01487. (DOI: 10.1002/ecs2.1487)

Abstract
We documented the frequency and effect on live biomass of five different types of disturbance over 14 years in creekbank and mid-marsh zones of eight salt marshes dominated by Spartina alterniflora in Georgia, USA. Wrack (floating debris) and creekbank slumping were the most common disturbances at the creekbank, and snails were the most common disturbance agent in the mid-marsh. Disturbance frequency varied among sites due to differences in plot elevation and landscape position. Wrack disturbance at the creekbank was positively correlated with plot elevation, and both initial slumping and terminal slumping of creekbank plots were negatively correlated with plot elevation. Wrack disturbance at the creekbank and snail disturbance in the mid-marsh were also most common at barrier island vs. interior marshes. Disturbance varied up to 14-fold among years. Wrack disturbance at the creekbank was negatively correlated with river discharge and sea level, and initial slumping of creekbank plots was also negatively correlated with sea level. The different disturbance types varied in their effects on end-of-year standing plant biomass. At the creekbank, wrack disturbance reduced biomass in affected plots by ~46%, but slumping did not affect biomass until the plot was totally lost. In the mid-marsh, slumping and wrack were not important disturbances, but snail disturbance reduced biomass in affected plots by ~70%. In addition, abiotic conditions (river discharge, maximum monthly temperature, sea level, and precipitation) strongly affected year-to-year variation in biomass. Across the entire landscape, fewer than a quarter of the plots on average were disturbed, and disturbance reduced overall standing biomass by ~18% in the creekbank zone and ~3% in the mid-marsh zone. Our results indicate that wrack has fairly strong effects on end-of-year biomass at the creekbank. Overall, however, variation in abiotic conditions among years had stronger effects on end-of-year standing biomass in both marsh zones than did disturbance.

Li, S. and Pennings, S.C. 2017. Timing of disturbance affects biomass and flowering of a saltmarsh plant and attack by stem-boring herbivores. Ecosphere. 8(2):9. (DOI: 10.1002/ecs2.1675)

Abstract
In salt marshes, disturbance by wrack (floating mats of dead vegetation) is common andaffects plant productivity and species composition, but little is known about how the timing of disturbance mediates these effects, nor how it interacts with herbivory. Using a field experiment on the Georgia coast, we simulated the effects of wrack disturbance at different times of the year on the marsh grass Spartina alterniflora and its stem-boring herbivorous insects. The timing of disturbance throughout the growing season strongly affected fall biomass, stem height, the proportion of stems flowering, and the proportion of stems colonized by stem-boring herbivorous insects. End-of-season biomass in plots disturbed in March did not differ from undisturbed controls, but biomass was reduced by 50% in plots disturbed in May, and by over 90% in plots disturbed in September. Disturbance in March and May stimulated flowering, but disturbance later in the growing season suppressed it. Plots disturbed late in the growing season had a low frequency of stem-boring herbivores. Stems containing stem borers rarely flowered. These results indicate that the timing of disturbance matters in coastal salt marshes. Late-season disturbances had the strongest effects on S. alterniflora and its herbivores. Disturbances early in the growing season did not affect endof-season biomass, and stimulated flowering, suggesting parallels between fire disturbance in grasslands and wrack disturbance in salt marshes. Late-season disturbance did reduce herbivory by stem-boring insects, but not enough to compensate for the direct effects of disturbance on the plants. Future studies of disturbance in salt marshes should consider how the timing of experimental disturbance treatments relates to the timing of natural disturbances.

Li, S., Hopkinson, C.S., Schubauer-Berigan, J.P. and Pennings, S.C. 2018. Climate drivers of Zizaniopsis miliacea biomass in a Georgia, U.S.A. tidal fresh marsh. Limnology and Oceanography. 63:2266-2276. (DOI: 10.1002/lno.10937)

Abstract
Tidal fresh marshes are at least as productive as nearby salt marshes, but much less is known about controlson primary production in tidal fresh vs. salt marshes. We studied a tidal fresh marsh in Georgia, U.S.A., dominatedby the C3 grass Zizaniopsis miliacea. We documented seasonal variation in Z. miliacea above-ground biomassand below-ground macro-organic matter over 1 yr, and annual variation in end-of-season abovegroundbiomass over 15 yr in creekbank and midmarsh zones. Aboveground biomass showed a distinct peak in Julyand October. Belowground macro-organic matter was much greater than aboveground biomass and peaked inOctober. Overall productivity was similar to that of salt marshes downstream. Z. miliacea end-of-season abovegroundbiomass showed a classic hump-shaped “subsidy-stress” relationship with plot elevation, but on averagethe creekbank supported about twofold more above-ground biomass than the midmarsh, and both zones variedin biomass about 1.7-fold among years. Annual variation in above-ground biomass was negatively correlatedwith maximum and mean temperature in both zones, and positively with river discharge in the creekbankzone. Sea level, precipitation and water column salinity showed biologically plausible trends with respect tobiomass. The responses of Z. miliacea to abiotic drivers were muted compared with the responses of nearby saltmarshes dominated by Spartina alterniflora. Temperature was more important for Z. miliacea, whereas drivers ofporewater salinity were more important in the salt marsh. Likely future changes in temperature, precipitation,and river discharge may pose a threat to the high productivity of tidal fresh marshes.

Li, S., Xie, T., Pennings, S.C., Wang, Y., Craft, C.B. and Hu, M. 2019. A comparison of coastal habitat restoration projects in China and the United States. Scientific Reports. 9(14388). (DOI: 10.1038/s41598-019-50930-6)

Li, X., Bellerby, R., Craft, C.B. and Widney, S. 2018. Coastal wetland loss, consequences, and challenges for restoration. Anthropocene Coasts. 1(1):1-15. (DOI: 10.1139/anc-2017-0001)

Abstract
Coastal wetlands mainly include ecosystems of mangroves, coral reefs, salt marsh, and sea grass beds. As the buffer zone between land and sea, they are frequently threatened from both sides. The world coastal wetland lost more than 50% of its area in the 20th century, largely before their great value, such as wave attenuation, erosion control, biodiversity support, and carbon sequestration, was fully recognized. World wetland loss and degradation was accelerated in the last three decades, caused by both anthropogenic and natural factors, such as land reclamation, aquaculture, urbanization, harbor and navigation channel construction, decreased sediment input from the catchments, sea level rise, and erosion. Aquaculture is one of the key destinations of coastal wetland transformation. Profound consequences have been caused by coastal wetland loss, such as habitat loss for wild species, CO2 and N2O emission from land reclamation and aquaculture, and flooding. Great efforts have been made to restore coastal wetlands, but challenges remain due to lack of knowledge about interactions between vegetation and morphological dynamics. Compromise among the different functionalities remains a challenge during restoration of coastal wetlands, especially when faced with highly profitable coastal land use. To solve the problem, multi-disciplinary efforts are needed from physio-chemical–biological monitoring to modelling, designing, and restoring practices with site-specific knowledge.

Li, X., Ren, Y., Lui, Y., Craft, C.B., Mander, U. and Tang, S. 2013. The impact of change in vegetation structure on the ecological functions of salt marshes: The example of the Yangtze River. Regional Environmental Change. 14(2):623-632. (DOI: 10.1007/s10113-013-0520-9)

Abstract
Salt marshes worldwide are faced with threats from rising sea levels and coastal development. We measured changes in salt marsh vegetation structure using remote sensing and its consequences for carbon sequestration, wave attenuation, and sediment trapping ability using remotely sensed imaging, field measurement data, and the published literature data pertaining to the Yangtze Estuary, a rapidly urbanizing area in Eastern China. From 1980 to 2010, the total area of vegetated salt marsh decreased by 17 %, but the vegetation structure changed more dramatically, with the ratio of Phragmites/Spartina/Scirpus changing from 24:0:76, to 77:0:23, 44:13:43, and 33:39:28 in 1980, 1990, 2000, and 2010, respectively. Carbon sequestration increased slightly from 1980 to 2010, with the dramatic shifts in plant species composition. The total length of seawall inadequately protected by salt marsh vegetation increased from 44 km in 1980 to 300 km in 2010. Sediment accretion increased (from 8 to 14 million m3/year) due to the spread of Spartina, which to some extent compensated the loss of total vegetated area in the salt marsh. Changes in the delivery of functions were not linearly related to the change in the area of vegetated salt marsh, but more from the combined effect of changing vegetation structure, sediment input, and land reclamation. Under threat of sea-level rise, protection and maintenance of vegetation structure outside the seawall are of great importance for the safe economic development inside the seawall.

Lin, W.-T. and Pennings, S.C. 2018. Predator-prey interactions in a ladybeetle-aphid system depend on spatial scale. Ecology and Evolution. 8:6537-6546.

Abstract
The outcome of species interactions may manifest differently at different spatial scales; therefore, our interpretation of observed interactions will depend on the scale at which observations are made. For example, in ladybeetle–aphid systems, the results from small-scale cage experiments usually cannot be extrapolated to landscape-scale field observations. To understand how ladybeetle–aphid interactions change across spatial scales, we evaluated predator–prey interactions in an experimental system. The experimental habitat consisted of 81 potted plants and was manipulated to facilitate analysis across four spatial scales. We also simulated a spatially explicit metacommunity model parallel to the experiment. In the experiment, we found that the negative effect of ladybeetles on aphids decreased with increasing spatial scales. This pattern can be explained by ladybeetles strongly suppressing aphids at small scales, but not colonizing distant patches fast enough to suppress aphids at larger scales. In the experiment, the positive effects of aphids on ladybee-tles were strongest at three-plant scale. In a model scenario where predators did not have demographic dynamics, we found, consistent with the experiment, that both the effects of ladybeetles on aphids and the effects of aphids on ladybeetles decreased with increasing spatial scales. These patterns suggest that dispersal was the primary cause of ladybeetle population dynamics in our experiment: aphids increased ladybeetle numbers at smaller scales because ladybeetles stayed in a patch longer and performed area-restricted searches after encountering aphids; these behaviors did not affect ladybeetle numbers at larger spatial scales. The parallel experimental and model results illustrate how predator–prey interactions can change across spatial scales, suggesting that our interpretation of observed predator–prey dynamics would differ if observations were made at different scales. This study demonstrates how studying ecological interactions at a range of scales can help link the results of small-scale ecological experiments to landscape-scale ecological problems.

Linsky, C.L. 2011. Guest Editorial: When teachers become scientists. Science Scope.

Abstract
Ask yourself this question: Have you ever worked on a real scientific experiment? Your thoughts may jump to the lab components of your undergraduate science courses and the research papers/assignments you completed in college, but should such structured, step-by-step exercises really be considered experiments? Is this what real scientists do? For the author, the answer to these questions about the true nature of science came in the form of two inspirational professional development courses where teachers become scientists. In this article, she describes her participation in the workshops and discusses how these experiences benefited her students back in the classroom as well.

Liu, Q., Lu, X., Tolar, B., Mou, X. and Hollibaugh, J.T. 2015. Concentrations, turnover rates and fluxes of polyamines in coastal waters of the South Atlantic Bight. Biogeochemistry. Online Early. (DOI: 10.1007/s10533-014-0056-1)

Abstract
Polyamines are short-chain aliphatic compounds containing multiple amine groups. They are important components of the cytosol of eukaryotes and are present at mmol L-1 concentrations inside phytoplankton cells, while complex polyamines play a role in biosilica deposition. Concentrations of polyamines measured in seawater are typically in the sub-nmol L-1 range, implying rapid and efficient uptake by osmotrophs, likely bacterioplankton. We measured turnover rates of 3 polyamines (putrescine, spermidine and spermine) using 3H-labeled compounds and determined their concentrations by HPLC to estimate polyamine contributions to dissolved organic matter and bacterioplankton carbon and nitrogen demand. These measurements were made on transects from the inner shelf to the Gulf Stream across the South Atlantic Bight (SAB) during April and October of 2011 and in salt marsh estuaries on the Georgia coast during August of 2011 and April of 2012. We found that turnover rates of polyamines were similar to those of amino acids (arginine and glutamic acid) measured in the same samples; however, fluxes of polyamines into bacterioplankton were much lower than amino acid fluxes as a result of low ambient concentrations. Turnover rates and fluxes of polyamines decreased from near-shore waters to the shelf-break, following the pattern of chlorophyll a concentration. Polyamine uptake accounted for less than 10% of bacterial N demand and 5% of bacterial C demand on average, with a large variation among water masses.

Liu, Q., Tolar, B., Ross, M., Cheek, J., Sweeney, C., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2018. Light and temperature control the seasonal distribution of Thaumarchaeota in the South Atlantic Bight. ISME Journal. 12:1473-1485. (DOI: 10.1038/s41396-018-0066-4)

Abstract
Previous work on the Georgia, USA coast revealed consistent mid-summer peaks in the abundance of Thaumarchaeota accompanied by spikes in nitrite concentration. We collected data on the distribution of Thaumarchaeota, ammonia-oxidizing Betaproteobacteria (AOB), nitrite-oxidizing Nitrospina, environmental variables and rates of ammonia oxidation during 6 cruises in the South Atlantic Bight from April to November 2014 to evaluate the areal extent and timing of the bloom. The abundance of Thaumarchaeota marker genes (16S rRNA and amoA) increased at inshore and nearshore stations starting in July and peaked in August at >107 copies L-1. The bloom did not extend onto the mid-shelf, where Thaumarchaeota genes ranged from 103 to 105 copies L-1. Clone libraries from samples collected at mid-shelf stations generated using Archaea 16S rRNA primers were dominated by sequences from Marine Group II and III Archaea, whereas libraries from inshore and nearshore stations were dominated by Thaumarchaeota. Thaumarchaeota were also abundant in oxygen-depleted waters at depth at the shelf-break. This population was phylogenetically-distinct from the inshore/nearshore population. Ammonia oxidation rates (AO) were highest at inshore stations and were at the limit of detection at mid-shelf stations. AO correlated significantly with ammonium concentration (r2=0.23) and Thaumarchaeota abundance (r2=0.14). Nitrite concentration correlated with AO (r2=0.74). Our analysis of environmental data suggests that Thaumarchaeota distributions in the SAB are controlled primarily by photoinhibition and secondarily by water temperature, while AO is controlled primarily by ammonium availability.

Liu, W. and Pennings, S.C. 2019. Self-thinning and size-dependent flowering of the grass Spartina alterniflora across space and time. Functional Ecology. 33:1830-1841. (DOI: 10.1111/1365-2435.13384)

Abstract
1. Plants adjust their size and reproductive effort in response to numerous selectionpressures and constraints. The self‐thinning law describes a well‐known trade‐offbetween size and density. Plants also trade‐off investment into growth vs. sexualreproduction, as described by life‐history theory.2. We build on past work on plant allometry and life history by examining both self‐thinning and size‐dependent reproduction in a single plant species, the saltmarshgrass Spartina alterniflora, across a wide range of settings: three landscape posi‐tions, two habitats and eight sites, across sixteen years.3. Plants in different landscape positions and years varied tremendously in size andshoot density. However, all this variation could be explained by a single allometricrelationship consistent with the self‐thinning law, but with a lower slope. Floweringwas size‐dependent, and the size at which plants had a 50% probability of flower‐ing varied among habitat, sites and years. Plants that were stressed reproducedat a smaller size than plants that were growing under good conditions, and thispattern was consistent among habitat, sites and years. Finally, reproductive bio‐mass and the proportion of shoots flowering increased with increasing vegetativesize (plant height or shoot biomass). Combining these two patterns, S. alternifloraplants growing high density are small and reproduce at a smaller size than largeplants growing at low density.4. Although there is tremendous spatial and temporal variation in S. alternifloragrowth and reproductive patterns, all this variation can be understood as result‐ing from two simple allometric trade‐offs. Because saltmarsh plants often occur inmonospecific stands, they may serve as simple, model systems for studies of plantlife history.

Liu, W., Chen, X., Strong, D.R., Pennings, S.C., Kirwan, M.L., Chen, X. and Zhang, Y. 2020. Climate and geographic adaptation drive latitudinal clines in biomass of a widespread saltmarsh plant in its native and introduced ranges. Limnology & Oceanography. 65:1399-1409. (DOI: 10.1002/lno.11395)

Abstract
Introduced plants provide a unique opportunity to examine how plants respond through plasticity and adaptationto changing climates. We compared plants of Spartina alterniflora from the native (United States, 27–43N)and introduced (China, 19–40N) ranges. In the field and greenhouse, aboveground productivity of Chineseplants was greater than that of North American plants. Aboveground biomass in the field declined with increasinglatitude in the native range, a pattern that persisted in the greenhouse, indicating a genetic basis. Abovegroundbiomass in the field displayed hump-shaped relationships with latitude in China, but this pattern disappeared infield and greenhouse common gardens, indicating phenotypic plasticity. Relationships in both geographic regionswere explained by temperature, which is probably the underlying environmental factor affecting abovegroundbiomass. S. alterniflora has evolved greater biomass in China, but in the four decades since it was introduced, ithas not yet evolved the genetic cline in biomass seen in its native range. By working at lower latitudes in theintroduced range than have been sampled in the native range, we identified an optimum temperature in theintroduced range above which aboveground productivity decreases.

Liu, W., Maung-Douglass, K., Strong, D.R., Pennings, S.C. and Zhang, Y. 2016. Geographical variation in vegetative growth and sexual reproduction of the invasive Spartina alterniflora in China. Journal of Ecology. 104:173-181. (DOI: 10.1111/1365-2745.12487)

Abstract
1. Phenotypic variation plays an important role in successful plant invasions. The spread of invasive species over large geographic ranges may be facilitated if plants can match their phenotype to local abiotic conditions. Spartina alterniflora, native to the United States, was introduced into China in 1979 and has spread over 19ᵒ of latitude along the eastern coast of China.2. We studied patterns in vegetative growth and sexual reproduction of S. alterniflora at 22 sites at 11 geographic locations over a latitudinal gradient of ~2000 km from Tanggu (39.05 °N, high latitude) to Leizhou (20.90 °N, low latitude) in China. We further evaluated the basis of phenotypic differences by growing plants from across the range in a common garden for 2 growing seasons.3. We found distinct latitudinal clines in plant height, shoot density, and sexual reproduction across latitude. Some traits exhibited linear relationships with latitude; others exhibited hump-shaped relationships. We identified correlations between plant traits and abiotic conditions such as mean annual temperature, growing degree days, tidal range, and soil nitrogen content. However, geographic variation in all but one trait disappeared in the common garden, indicating that variation largely due to phenotypic plasticity. Only a slight tendency for latitudinal variation in seed set persisted for two years in the common garden, suggesting that plants may be evolving genetic clines for this trait.4. Synthesis. The rapid spread of Spartina alterniflora (S. alterniflora) in China has probably been facilitated by phenotypic plasticity in growth and reproductive traits. We found little evidence for the evolution of genetic clines in China, even though these exist for some traits in the native range. The considerable variation among clones, within provenances, that persisted in the common garden suggests a potential for the evolution of geographic clines in the future. Low fecundity of low latitude S. alterniflora populations in China might result in a slower spread atlow latitudes, but S. alterniflora is likely to continue to spread rapidly at high latitudes in China and into the Korean peninsula.

Liu, W., Strong, D.R., Pennings, S.C. and Zhang, Y. 2017. Provenance-by-environment interaction of reproductive traits in the invasion of Spartina alterniflora in China. Ecology. 98(6):1591-1599. (DOI: 10.1002/ecy.1815)

Abstract
Ecological invasions are facilitated by pre-adaptation and phenotypic plasticity, upon which evolution can act. The rapid invasion of the intertidal grass Spartina alterniflora in China during the last 36 yr is a test case for the roles of these mechanisms. A previous study of S. alterniflora in China found strong latitudinal clines in vegetative and sexual traits and concluded that most of this variation was due to phenotypic plasticity. Recent observations suggested provenance-by-environment interactions, and we employed common gardens at multiple latitudes as a test of this idea. Phenotypically, field plant height, which correlates strongly with biomass and other indices of vegetative performance in this species, showed a hump-shaped relationship across 10 sites, covering 19° of latitude; field seed set increased linearly with latitude. To assess the role of plasticity vs. genetic differentiation in these patterns, we grew plants from the ten field sites in three common gardens at low (20.9° N), mid (28.3° N), and high (38.0° N) latitudes to maturity, at 18 months. Plant height varied among common gardens, with the tallest plants at mid latitude, mirroring the field pattern, consistent with the previous study. Within the gardens, latitude of origin also affected plant height. Seed set varied among the gardens, with the greatest values at high latitudes, again mirroring the field pattern and indicating substantial plasticity. Evidence of evolution was found as increasing seed set with latitude among provenances within common gardens. However, the effect differed among common gardens, with the greatest slope in the high-latitude garden, lower slope in the mid-latitude garden, and no relationship in the low-latitude garden, indicating a provenance-by-environment interaction. The number of surviving plants also suggested a provenance-by-environment interaction; no relationship with latitude among provenances in the two southern gardens and increasing survival with latitude in the northern garden. Field seedling density was ~200-fold greater at high than at low latitude sites. The profuse seed germination and recruitment in the north could have created high selection intensity resulting in evolution of reproductive traits at high latitudes with the result that the mechanisms of the invasion differ with latitude.

Loftis, K. and Meile, C. 2014. Isotopes and elemental ratios in multi-parameter mixing models. Limnology and Oceanography: Methods. 12:694-702. (DOI: 10.4319/lom.2014.12.694)

Abstract
Concentration measurements, stable isotope signatures, and elemental ratios are extensively used as parameters in mixing models to identify the source material contributing to mixtures. Determining these contributions in complex mixtures necessitates the use of multiple tracers. Here, we show that this requires careful selection of the parameters used, and that the common direct use of isotopic signatures or elemental ratios in mixing models when combined with other tracers can lead to erroneous results. We further demonstrate that when the number of available tracers exceeds the number of source materials, finding the fractional contributions that best fit the data may benefit from normalization, and we present a simple measure indicating when the outcome of mixing model calculations is poorly constrained. Finally, as a practical example, we investigated the impact of parameter choices through a reanalysis of literature data on organic matter cycling along the Altamaha River Estuary.

Loomis, M.J. and Craft, C.B. 2010. Carbon sequestration and nutrient (N, P) accumulation in river-dominated tidal marshes, Georgia, USA. Soil Science Society of America Journal. 74:1028-1038. (DOI: 10.2136/sssaj2009.0171)

Abstract
Soil organic C, N, and P were measured in salt, brackish, and tidal freshwater marshes in river-dominated estuaries (Ogeechee, Altamaha, and Satilla) of the Georgia coast to evaluate the effects of salinity on C, N, and P storageand accumulation. Tidal freshwater marshes had greater concentrations of organic C (10.81% w/w) and N (0.71% w/w)than brackish (7.71% C, 0.50% N) or salt (5.95% C, 0.35% N) marshes. Soil accretion rates of ^137Cs were greaterin tidal freshwater (4.78 mm yr^1) and brackish marshes (4.41 mm yr^1) than in salt marshes (1.91 mm yr^1). Consequently, organic C and N accumulation was greater in tidal freshwater (124 and 8.2 g m^2 yr^1) and brackish (93 and 6.5 g m^2 yr^1) marshes than salt marshes (40 and 2.4 g m^2 yr^1). Phosphorus accumulation was greater in the brackish marshes. Lower salinity tidal freshwater and brackish marshes remove more C, N, and P; however, salt marshes dominate the spatial extent of the study area (60%) vs. brackish (33%) and tidal freshwater marshes (7%). Combinig measurements of C, N, and P accumulation with tidal marsh area, we estimated that tidal freshwater, brackish, and salt marshes stored or removed the equivalent of 2 to 20% of watershed N inputs entering the estuaries from the terrestrial landscape. After accounting for N2 fixation and denitrification, tidal marshes collectively removed the equivalent of 13 to 32% of the N entering estuaries. Tidal marshes, especially tidal freshwater and brackish marshes, are important for improving water quality and decreasing the impacts of Neutrophication of estuarine ecosystems.

Lu, X., Sun, S., Hollibaugh, J.T. and Mou, X. 2015. Identification of polyamine-responsive bacterioplankton taxa in South Atlantic Bight. Environmental Microbiology Reports. 7(6):831-838. (DOI: 10.1111/1758-2229.12311)

Abstract
Putrescine and spermidine are short-chained aliphatic polyamines (PAs) that are ubiquitously distributed in seawater. These compounds may be important sources of dissolved organic carbon and nitrogen for marine bacterioplankton. Here, we used pyrotag sequencing to quantify the response of bacterioplankton to putrescine and spermidine amendments in microcosms established using surface waters collected at various stations in the South Atlantic Bight in October 2011. Our analysis showed that PA-responsive bacterioplankton consisted of bacterial taxa that are typically dominant in marine systems. Rhodobacteraceae (Alphaproteobacteria) was the taxon most responsive to PA additions at the nearshore site. Gammaproteobacteria of the families Piscirickettsiaceae; Vibrionaceae; and Vibrionaceae and Pseudoalteromonadaceae, were the dominant PA-responsive taxa in samples from the river-influenced coastal station, offshore station and open ocean station, respectively. The spatial variability of PA-responsive taxa may be attributed to differences in composition of the initial bacterial community and variations of in situ physiochemical conditions among sites. Our results also provided the first empirical evidence that Gammaproteobacteria might play an important role in PA transformation in marine systems.

Lulewicz, I.H., Thompson, V.D., Cramb, J. and Tucker, B. 2017. Oyster paleoecology and Native American subsistence practices on Ossabaw Island, Georgia, USA. Journal of Archaeological Science: Reports. 15:282 - 289. (DOI: 10.1016/j.jasrep.2017.07.028)

Abstract
We examined the shell size of 3262 eastern oysters (Crassostrea virginica) to assess diachronic patterns in shellfish exploitation on Ossabaw Island, Georgia. These measurements taken on shell size and morphology were compared between a Late Archaic shell ring, a Late Woodland shell-filled pit, and a Late Mississippian midden-mound to evaluate changes in oyster population ecology, as it related to large scale changing environmental conditions and Native America subsistence practices over time. Our results indicate stability in oyster populations during the Late Archaic with a following decrease in oyster size through the Late Woodland into the Late Mississippian. We attribute this decrease to combination to human predation and large-scale climate fluctuations, with the latter being the primary driver of this shift in size.

Lulewicz, I.H., Thompson, V.D., Pluckhahn, T.J., Andrus, C.F. and Das, O. 2018. Exploring Oyster (Crassostrea virginica) Habitat Collection via Oxygen Isotope Geochemistry and its Implications for Ritual and Mound Construction at Crystal River and Roberts Island, Florida. The Journal of Island and Coastal Archaeology. 13(3):388-404. (DOI: 10.1080/15564894.2017.1363096)

Abstract
Research at Crystal River and Roberts Island Shell Mound Complex, on the western coast of Florida, USA, offers a quantitative assessment of the temporality of shell deposit construction, Native subsistence practices, and mobility patterns through stable oxygen isotope data from eastern oyster (C. virginica). The δ18Owater values of oysters vary synchronously with salinity, assuming relatively constant δ18Owater/salinity gradients since the time of occupation, allowing for an examination of shifts in oyster habitat exploitation over time. Our previous (Thompson et al. 2015) study indicated that midden accumulation occurred throughout the year, while oysters from mound deposits were collected in colder months. New data indicate that in addition to differential season of collection, habitat exploitation also varied. During early occupation at the site, oysters were collected primarily from lower saline habitats, while in later phases oysters were obtained from higher salinity waters; we relate this to a lower sea level and concomitant settlement shift seaward. Additionally, oyster from later mound contexts was collected from higher saline habitats relative to those in midden contexts; Native people may have targeted specific bioherms at certain times for the year for feasting-related mound construction.

Lyons, J.I., Alber, M. and Hollibaugh, J.T. 2010. Ascomycete fungal communities associated with early decaying leaves of Spartina spp. from central California estuaries. Oecologica. 162:435-442. (DOI: 10.1007/s00442-009-1460-4)

Abstract
Ascomycetous fungi play an important role in the early stages of decomposition of Spartina alterniflora, but their role in the decomposition of other Spartina species has not been investigated. Here we use fingerprint (T-RFLP) and phylogenetic analyses of the 18S-to-28S internal transcribed spacer (ITS) region to compare the composition of the ascomycete fungal communities on early decay blades of Spartina species (S. alterniflora, S. densiflora, S. foliosa, and a hybrid (S. alterniflora x S. foliosa) collected from three salt marshes in San Francisco Bay and one in Tomales Bay, California, U.S.A. Phaeosphaeria spartinicola was found on all samples collected and was often dominant. Two other ascomycetes, Phaeosphaeria halima and Mycosphaerella sp. strain 2, were also common. These three species are the same ascomycetes previously identified as the dominant fungal decomposers on S. alterniflora on the east coast. Ascomycetes appeared to exhibit varying degrees of host-specificity, demonstrated by grouping patterns on phylogenetic trees. Neither the exotic S. alterniflora nor the hybrid supported fungal flora different from that of the native S. foliosa. However, S. densiflora had a significantly different fungal community than the other species, and hosted at least two unique ascomycetes. Significant differences in the fungal decomposer communities were also detected within species (two clones of S. foliosa), but these were minor and may be due to morphological differences among the plants.

Lyons, J.I., Newell, S.Y., Brown, R.P. and Moran, M.A. 2005. Screening for bacterial-fungal associations in a southeastern U.S. salt marsh using pre-established fungal monocultures. FEMS Microbiology Ecology. 54:179-187.

Abstract
Both bacteria and fungi play critical roles in decomposition processes in many natural environments, yet only rarely have they been studied as an integrated community. We examined whether physical associations exist between individual bacterial and fungal species that co-occur on decaying smooth cordgrass, Spartina alterniflora, in a south-eastern US salt marsh. Fungal-pervaded decaying Spartina was used as "bait" for potential bacterial associates. The bundles (infiltrated with one of three dominant fungal members of the decomposer assemblage, or an autoclaved control) were placed in a salt marsh and collected biweekly for 6 weeks during the first experiment (late summer 2002), and weekly for 3 weeks during the second experiment (early summer 2003). Terminalrestriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes was used to track colonization by bacterial taxa in association with the established fungal species. T-RFLP analysis of 18S-to-28S internal transcribed spacer (ITS) regions was used to monitor changes in fungal communities once bundles had been placed in the field. Results from both years were nearly identical, and showed that invasion by fungi other than the bait species was slow, resulting in a virtual fungal monoculture for several weeks into the experiments. Surprisingly, bacterial communities were una.ected by the identity of the fungal bait. Regardless of the fungal species, and even in the absence of prior fungal colonization, bacterial 16S rRNA profiles were remarkably similar. These results suggest that few species-specific associations, either positive or negative, exist between bacterial and fungal members of the Spartina decomposer community during initial colonization.

Lyons, J.I., Newell, S.Y., Buchan, A. and Moran, M.A. 2003. Diversity of ascomycete laccase gene sequences in a southeastern U.S. salt marsh. Microbial Ecology. 45:270-281.

Abstract
The diversity of ascomycete laccase sequences was surveyed in a southeastern U.S. salt marsh using a degenerate primer set designed around copper binding sites conserved in fungal laccases. This gene was targeted for diversity analysis because of its potential function in lignin degradation in the salt marsh ecosystem and because few studies have assessed functional gene diversity in natural fungal communities. Laccase sequences were amplified from genomic DNA extracted from twenty four isolates (representing ten ascomycete species) cultured from decaying blades of Spartina alterniflora, and from DNA extracted directly from the decaying blades. Among the ascomycete isolates, twenty-one yielded a PCR product of expected size (~900 bp) that was tentatively identified as laccase based on sequence similarities to previously published laccase sequences from related organisms. Overall, thirteen distinct sequence types, containing 39 distinct sequences, were identified among the isolates, with several species yielding multiple distinct laccase types. PCR amplifications from early and late decay blades of S. alterniflora yielded seven laccase types. Of these, five were composed of sequences >96% similar at the amino acid level to sequences from three cultured ascomycetes previously found to be dominant members of the fungal communities on decaying S. alterniflora blades. Two of the laccase types from the natural-decay clone library were novel, and did not match any of the sequences obtained from the cultured ascomycetes. The 39 distinct sequences and fifteen distinct laccase sequence types retrieved from the S. alterniflora decay system demonstrate high sequence diversity of this functional gene in a natural fungal community.

Magalhăes, C.M., Joye, S.B., Moreira, R.M., Wiebe, W.J. and Bordalo, A.A. 2005. Effect of salinity and inorganic nitrogen concentrations on nitrification and denitrification rates in intertidal sediments and rocky biofilms of the Douro River estuary, Portugal. Water Research. 39:1783–1794.

Abstract
The regulatory effects of salinity and inorganic nitrogen compounds on nitriflcation and denitrification were studied in intertidal sandy sediments and rocky biofilms in the Douro River estuary, Portugal, over a 12-month period. Nitrification and denitrification rates were measured in slurries of field samples and enrichment experiments using the difiuoromethane and the acetylene inhibition techniques, respectively. Salinity did not regulate denitrification in either environment, suggesting that halotolerant bacteria dominated the denitrifier communities. However, nitrification rates were stimulated when salinity increased from 0 to 15 practical salinity units. NO3- addition experiments revealed that NO3- availability stimulates denitrification rates in sandy sediments, but not in rocky biofilms; however, in rocky biofilms a positive and linear relationship was observed between denitrification rates and water column NO3- concentrations (r = 0.92) during the monthly surveys. The N2O:N2 ratios increased rapidly when NO3- increased from 63 to 363 uM; however, results from monthly surveys showed that environmental parameters other than NO3- availability may be important in controlling the variation in N2O production via denitrification. Ammonium additions to sandy sediments stimulated nitrification rates by 35% for the 20 uM NH4+ addition, but NH4+ appeared to inhibit nitrification at high concentration addition (200 uM NH4+). In contrast, rocky biofilm nitrification was stimulated by 65% when 200 uM NH4+ was added.

Magalhăes, C.M., Wiebe, W.J., Joye, S.B. and Bordalo, A.A. 2005. Inorganic Nitrogen Dynamics in Intertidal Rocky Biofilms and Sediments of the Douro River Estuary (Portugal). Estuaries, 28(4): 592-607.

Abstract
In this study rates of oxygen, ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), and nitrous oxide (N2O) fluxes, nitrogen (N) fixation, nitrification, and denitrification were compared between two intertidal sites for which there is an abundant global literature, muddy and sandy sediments, and two sites representing the rocky intertidal zone where biogeochemical processes have scarcely been investigated. In almost all sites oxygen production rates greatly exceeded oxygen consumption rates. During daylight, NH4+ and NO3- uptake rates together with ammonification could supply the different N requirements of the primary producer communities at all four sites; N assimilation by benthic or epilithic primary producers was the major process of dissolved inorganic nitrogen (DIN) removal; N fixation, nitrification, and denitrification were minor processes in the overall light DIN cycle. At night, distinct DIN cycling processes took place in the four environments, denitrification rates ranged from 9 +/- 2 to 360 +/- 30 mmol N2 m^-2 h^-1, accounting for 10–48% of the water column NO3- uptake; nitrification rates varied from 0 to 1712 +/- 666 mmol NH4+ m^-2 h^-1. A conceptual model of N cycle dynamics showed major differences between intertidal sediment and rocky sites in terms of the mean rates of DIN net fluxes and the processes involved, with rocky biofilm showing generally higher fluxes. Of particular significance, the intertidal rocky biofilms released 10 times the amount of N2O produced in intertidal sediments (up to 17 +/- 6 mmol N2O m^-2 h^-1), representing the highest N2O release rates ever recorded for marine systems. The biogeochemical contributions of intertidal rocky substrata to estuarine and coastal processes warrant future detailed investigation.

Mahmoudi, N., Porter, T., Zimmerman, A., Fulthopre, R., Kasozi, G., Slater, G. and Silliman, B.R. 2013. Rapid degradation of Deepwater Horizon spilled oil by indigenous microbial communities in Louisiana salt marsh sediments. Environmental Science and Technology. 47(23):13303-13312. (DOI: 10.1021/es4036072)

Abstract
The Deepwater Horizon oil spill led to the severe contamination of coastal environments in the Gulf of Mexico. A previous study detailed coastal saltmarsh erosion and recovery in a number of oil-impacted and nonimpacted reference sites in Barataria Bay, Louisiana over the first 18 months after the spill. Concentrations of alkanes and polyaromatic hydrocarbons (PAHs) at oil-impacted sites significantly decreased over this time period. Here, a combination of DNA, lipid, and isotopic approaches confirm that microbial biodegradation was contributing to the observed petroleum mass loss. Natural abundance 14C analysis of microbial phospholipid fatty acids (PLFA) reveals that petroleum-derived carbon was a primary carbon source for microbial communities at impacted sites several months following oil intrusion when the highest concentrations of oil were present. Also at this time, microbial community analysis suggests that community structure of all three domains has shifted with the intrusion of oil. These results suggest that Gulf of Mexico marsh sediments have considerable biodegradation potential and that natural attenuation is playing a role in impacted sites.

Marczak, L., Ho, C.-K., Vu, H., Denno, R. and Pennings, S.C. 2011. Latitudinal variation in top-down and bottom-up control of a salt marsh food web. Ecology. 92:276-281. (DOI: 10.1890/10-0760.1)

Abstract
The shrub Iva frutescens, which occupies the terrestrial border of U.S. Atlantic Coast salt marshes, supports a food web that varies strongly across latitude. We tested whether latitudinal variation in plant quality (higher at high latitudes), consumption by omnivores (a crab, present only at low latitudes), consumption by mesopredators (ladybugs, present at all latitudes), or the life history stage of an herbivorous beetle could explain continental-scale field patterns of herbivore density. In a mesocosm experiment, crabs exerted strong top-down control on herbivorous beetles, ladybugs exerted strong top-down control on aphids, and both predators benefited plants through trophic cascades. Latitude of plant origin had no effect on consumers. Herbivorous beetle density was greater if mesocosms were stocked with beetle adults rather than larvae, and aphid densities were reduced in the “adult beetle” treatment. Treatment combinations representing high and low latitudes produced patterns of herbivore density similar to those in the field. We conclude that latitudinal variation in plant quality is less important than latitudinal variation in top consumers and competition in mediating food web structure. Climate may also play a strong role in structuring high-latitude salt marshes by limiting the number of herbivore generations per growing season and causing high overwintering mortality.

Marczak, L., Wieski, K., Denno, R. and Pennings, S.C. 2013. Importance of local vs. geographic variation in salt marsh plant quality for arthropod herbivore communities. Journal of Ecology. 101:1169-1182. (DOI: 10.1111/1365-2745.12137)

Abstract
1. An important recent advance in food web ecology has been the application of theory regarding spatial gradients to studies of the factors that affect animal population dynamics. Building on extensive studies of the Spartina alterniflora food web at the local scale, we hypothesized that geographic variation in S. alterniflora quality is an important bottom-up control on food web structure and that geographic variation in S. alterniflora quality would interact with the presence of predators and top omnivores to mediate herbivore densities.2. We employed a four-factor fully crossed experiment in which we (i) collected plants from high and low-latitude locations and grew them in a common garden and varied (ii) plant fertilization status (mimicking the plant quality differences due to marsh elevation), (iii) mesopredator density and (iv) omnivore density.3. Our results suggest that the single most important factor mediating insect herbivore densities is local variation in plant quality – induced in our experiment by fertilization and demonstrated repeatedly as a consequence of marsh elevation.4. Top-down effects were generally weak and in those cases where predators did exert a significant suppressing effect on herbivores, that impact was itself mediated by host-plant characteristics.5. Finally, despite observed variation in plant quality with latitude, and the separately measurable effects of this variation on herbivores, geographic-scale variation in plant quality was overwhelmed by local conditions in our experiments.6. Synthesis. We suggest that a first-order understanding of variation across large latitudinal ranges in the Spartina alterniflora arthropod food web must begin with local variation in plant quality, which provides strong bottom-up forcing to herbivore populations. A second-order understanding of the arthropod food web should consider the role of predation in controlling herbivores feeding on low quality plants. Finally, while latitudinal variation in plant quality probably explains some variation in herbivore densities, it is probably more of a response to herbivore pressure than a driver of the herbivore dynamics. Although extrapolating from local to geographic scales presents multiple challenges, it is an essential task in order for us to develop an understanding that is general rather than site-specific.

Marton, J., Herbert, E. and Craft, C.B. 2012. Effects of Salinity on Denitrification and Greenhouse Gas Production from Laboratory-incubated Tidal Forest Soils. Wetlands. 32:347-357. (DOI: 10.1007/s13157-012-0270-3)

Abstract
We measured ambient and potential denitrification in tidal freshwater floodplain forest (tidal forests) soils along the Altamaha, Ogeechee, and Satilla Rivers in southeast Georgia to characterize nitrogen removal from these understudied systems. Further, we measured the response of denitrification, greenhouse gas production (CO 2 , CH 4 , N 2 O), and the formation of reduced inorganic sulfur species following laboratory incubations simulating saltwater intrusion with salinity levels of 2 and 5. Ambient denitrification ranged from 0.03 µg N 2 O/g/hr in the Satilla River to 0.40 µg N 2 O/g/hr in the Altamaha River. Potential denitrification was two to eight times greater than ambient denitrification. Denitrification from Satilla River soils increased with salinity, while Altamaha and Ogeechee River soils were unaffected. Methane production, however, was inhibited by salinity, decreasing by 77% in the 2 treatment and 89% in the 5 treatment whereas CO 2 generally increased with salinity, though exhibited a variable response between the three rivers. Formation of reduced sulfur species followed a similar trend to CO 2 production. Our findings suggest that tidal forests are effective sinks for N, capable of producing anywhere from 0.032 to 1.9 µg N 2 O/g soil/hr. Overall, salinity increased the amount of C mineralized suggesting that low levels of salinity can alter the short-term C dynamics of tidal freshwater forests.

McCall, B.D. and Pennings, S.C. 2012. Disturbance and recovery of salt marsh arthropod communities following BP Deepwater Horizon oil spill. PLoS ONE. (DOI: 10.1371/journal.pone.0032735)

Abstract
Oil spills represent a major environmental threat to coastal wetlands, which provide a variety of critical ecosystem services to humanity. The U.S. Gulf of Mexico is a hub of oil and gas exploration activities that historically have impacted intertidal habitats such as salt marsh. Following the BP Deepwater Horizon oil spill, we sampled the terrestrial arthropod community and marine invertebrates found in stands of Spartina alterniflora, the most abundant plant in coastal salt marshes. Samplingoccurred in 2010 as oil was washing ashore and a year later in 2011. In 2010, intertidal crabs and terrestrial arthropods (insects and spiders) were suppressed by oil exposure even in seemingly unaffected stands of plants; however, Littorariasnails were unaffected. One year later, crab and arthropods had largely recovered. Our work is the first attempt that we know of assessing vulnerability of the salt marsh arthropod community to oil exposure, and it suggests that arthropods areboth quite vulnerable to oil exposure and quite resilient, able to recover from exposure within a year if host plants remain healthy.

McCall, B.D. and Pennings, S.C. 2012. Geographic variation in salt marsh structure and function. Oecologia. 170:777-787. (DOI: 10.1007/s00442-012-2352-6)

Abstract
We examined geographic variation in the structure and function of salt marsh communities along the Atlantic and Gulf coasts of the United States. Focusing on the arthropod community in the dominant salt marsh plant Spartina alterniflora, we tested two hypotheses: first, that marsh community structure varies geographically, and second, that two aspects of marsh function (response to eutrophication and addition of dead plant material) also vary geographically. We worked at eleven sites on the Gulf Coast and eleven sites on the Atlantic Coast, dividing each coast up into two geographic areas. Abiotic conditions (tidal range, soil organic content, and water content, but not soil salinity), plant variables (Spartina nitrogen content, height, cover of dead plant material, but not live Spartina percent cover or light interception), and arthropod variables (proportional abundances of predators, sucking herbivores, stem-boring herbivores, parasitoids, and detritivores, but not total arthropod numbers) varied among the four geographic regions. Latitude and mean tidal range explained much of this geographic variation. Nutrient enrichment increased all arthropod functional groups in the community, consistent with previous experimental results, and had similar effects in all geographic regions, contrary to our hypothesis, suggesting widespread consistency in this aspect of ecosystem function. The addition of dead plant material had surprisingly little effect on the arthropod community. Our results caution against the uncritical extrapolation of work done in one geographic region to another, but indicate that some aspects of marsh function may operate in similar ways in different geographic regions, despite spatial variation in community structure.

McFarlin, C.R. and Alber, M. 2013. Foliar DMSO:DMSP ratio and metal content as indicators of stress in Spartina alterniflora. Marine Ecology Progress Series. 474:1-13. (DOI: 10.3354/meps10184)

Abstract
We evaluated 2 potential indicators of stress, viz. the ratio of dimethylsulfoxide to dimethylsulfoniopropionate (DMSO:DMSP) and foliar metals, in Spartina alterniflora collected from areas affected by 4 different disturbances (sudden marsh dieback,horse grazing, increased snail densities, wrack deposition) across 20 marshes in Georgia, USA. The DMSO:DMSP ratio was a stronger and more consistent indicator of stress than either DMSP or DMSO concentrations alone, with significantly higher ratios occurring in leaves and stems collected from affected compared to healthy areas in all 4 disturbance types. Foliar metal concentrations also differed in affectedcompared to healthy areas. Of 20 metals evaluated, concentrations of 19 were increased in leaves collected from edge and affected areas. Multidimensional scaling using the entire suite of metals showed separation between plants from affected and healthy areas, but no difference among disturbance types. In contrast, chlorophyll a concentrations were not significantly different between affected and healthy areas, and did not correlate with variation in either of the 2 indicators. These results suggest that the DMSO:DMSP ratio and foliar metal suite are sensitive indicators of sublethal stress in Spartina, capable of identifying stress before there are visible signs such as chlorophyll loss. The fact that both indicators were consistent across a variety of disturbance types suggests that they may be primarily responsive to general oxidative stress and thus, broadly useful tools for evaluating the health of salt marsh habitat in the field.

McFarlin, C.R., Bishop, T.D., Hester, M. and Alber, M. 2015. Context-dependent effects of the loss of Spartina alterniflora on salt marsh invertebrate communities. Estuarine, Coastal and Shelf Science. 163:218-230. (DOI: 10.1016/j.ecss.2015.05.045)

Abstract
Sudden dieback of the salt marsh grass Spartina alterniflora during 2000-2002 transformed once-vegetated areas to bare sediment in coastal Georgia and Louisiana. We investigated the effects of losing this foundation species on habitat provisioning for benthic epifauna, macroinfauna, and meiofauna in these distinct geographical regions. In GA, significant shifts in invertebrate community assemblages were observed between bare and reference (vegetated) plots, with abundances of all invertebrate groups and the diversity of macroinfauna lower in bare plots. In LA, community assemblages overlapped considerably in dieback and reference plots. Although epifaunal snails were significantly decreased in dieback plots, meiofauna were unexpectedly increased. Other invertebrates did not differ between plots. Supplemental transplanted plots allowed for direct evaluation of stem density effects on invertebrates. Stem density predicted abundances of all invertebrate groups in GA, and was positively correlated with increased soil moisture. In LA, elevation and soil moisture were good predictors of infauna but were not related to stem density. Differences between the states suggest that S. alterniflora may not provide equivalent ecosystem services in all salt marshes. Additional disturbances (drought, GA; hurricanes, LA) decreased infaunal density and taxon richness in 2008. However, in both states the reduction of macroinfauna was larger in bare than reference areas, suggesting that vegetation protected against further disturbance. Our results suggest that the role of S. alterniflora is context-dependent both in terms of geographic setting and the specific ecosystem service under consideration.

McFarlin, C.R., Brewer, J.S., Buck, T.L. and Pennings, S.C. 2008. Impact of fertilization on a salt marsh food web in Georgia. Estuaries and Coasts. 31:313-325.

Abstract
We examined the response of a salt marsh food web to increases in nutrients at 19 coastal sites in Georgia. Fertilization increased the nitrogen content of the two dominant plants, Spartina alterniflora and Juncus roemerianus, indicating that added nutrients were available to and taken up by both species. Fertilization increased Spartina cover, height and biomass and Juncus height, but led to decreases in Juncus cover and biomass. Fertilization increased abundances of herbivores (grasshoppers) and herbivore damage, but had little effect on decomposers (fungi), and no effect on detritivores (snails). In the laboratory, herbivores and detritivores did not show a feeding preference for fertilized versus control plants of either species, nor did detritivores grow more rapidly on fertilized versus control plants, suggesting that changes in herbivore abundance in the field were driven more by plant size or appearance than by plant nutritional quality. Community patterns in control plots varied predictably among sites (i.e. 17 of 20 regression models examining variation in biological variables across sites were significant), but variation in the effects of fertilization across sites could not be easily predicted (i.e. only 6 of 20 models were significant). Natural variation among sites was typically similar or greater than impacts of fertilization when both were assessed using the coefficient of variation. Overall, these results suggest that eutrophication of salt marshes is likely to have stronger impacts on plants and herbivores than on decomposers and detritivores, and that impacts at any particular site might be hard to distinguish from natural variation among sites.

McKay, P. and Di Iorio, D. 2008. Heat budget for a shallow, sinuous salt marsh estuary. Continental Shelf Research. 28:1740–1753. (DOI: 10.1016/j.csr.2008.04.008)

Abstract
An experimental study of temperature cycles and the heat budget in the Duplin River, a tidal creek bordered by extensive intertidal salt marshes, was carried out in late summer of 2003 and spring of 2004 near Sapelo Island on the central Georgia coast in the southeastern US. Three water masses are identified with differing temperature and salinity regimes, the characteristics of which are dictated by channel morphology, tidal communication with the neighboring sound, ground water hydrology, the extent of local intertidal salt marshes and side channels and the spring–neap tidal cycle (which controls both energetic mixing and, presumably, ground water input). For the first experiment, heat budgets are constructed for the upper (warmer) and lower (cooler) areas of the Duplin River showing the diminishing importance of tidal advection away from the mouth of the creek along with the concomitant increase in the importance of both direct atmospheric fluxes and of interactions with the marsh and side creeks. The second experiment, in the spring of 2004, reexamines the heat budget on seasonal and daily averaged scales revealing the decreased importance of advective fluxes relative to direct atmospheric fluxes on this scale but the constant importance of marsh/creek interactions regardless of time scale or season. Short period temperature fluctuations which affect larval development are examined and analogies are drawn to use heat to understand the marsh as a source of sediment, carbon and other nutrients.

McKay, P. and Di Iorio, D. 2010. The Cycle of Vertical and Horizontal Mixing in a Tidal Creek. Journal of Geophysical Research. 115:C01004. (DOI: 10.1029/2008JC005204)

Abstract
An experimental study of vertical mixing and along-channel dispersion parameterizedin terms of horizontal mixing near the mouth of the Duplin River (a tidal creek borderedby extensive intertidal salt marshes on Sapelo Island, Georgia) was carried out overseveral spring/neap cycles in the fall of 2005. Vertical mixing is modulated on both M4and fortnightly frequencies with maximum turbulent stresses being generated near thebed on periods of maximum flood and ebb and propagating into the water columnshowing a linear dependence with depth. Values are significantly greater on spring tidethan on neap. Horizontal mixing evaluated by salt fluxes is driven and dominated bytidal dispersion, which is also modulated by the fortnightly spring/neap cycle. Net export of salt from the lower Duplin is shown to be due to residual advection modified by upstream tidal pumping. The tidal dispersion coefficient exhibits a pulsating character with greater values on spring tide followed by smaller values on neap tide.

Mcleod, E., Chmura, G.L., Bouillon, S., Salm, R., Bjork, M., Duarte, C.M., Lovelock, C.E., Schlesinger, W.H. and Silliman, B.R. 2011. A Blueprint for Blue Carbon: Towards an improved understanding of the role of vegetated coastal habitats in sequestering CO2. Frontiers in Ecology and the Environment. 9(10):552=560. (DOI: 10.1890/110004)

Abstract
Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO2). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed “blue carbon”. Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of their C sequestration value provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them.

Medeiros, P.M., Babcock-Adams, L., Seidel, M., Castelao, R., Di Iorio, D., Hollibaugh, J.T. and Dittmar, T. 2017. Export of terrigenous dissolved organic matter in a broad continental shelf. Limnology & Oceanography. 62:1718-1731. (DOI: 10.1002/lno.10528)

Abstract
Export of terrigenous dissolved organic matter (DOM) from rivers to the ocean plays an important role in the carbon cycle. Observations from six research cruises in 2014 were used to characterize the seasonal evolution of terrigenous DOM in the shallow and broad South Atlantic Bight (SAB) shelf. While DOM with a strong terrigenous molecular, optical and isotopic signature was restricted to a coastal band early in the year, a plume with terrigenous DOM extended further to the shelf break in late spring. The offshore transport of this terrigenous DOM was consistent with wind-driven advection in a surface Ekman layer. On time scales spanning about 1 month, the traceable riverine DOM compounds were mostly resistant to bio- and photo-degradation, and the decrease in their relative abundance over the shelf following peak river discharge during spring was consistent with dilution of the river plume due to entrainment of oceanic water associated with wind-driven mixing. Comparisons between optical absorbance measurements and ultrahigh resolution mass spectrometry data revealed that the fraction of the DOM pool with a riverine signature in the SAB can be estimated using the spectral slope coefficient of chromophoric DOM in the 275–295 nm range. This finding opens up the possibility of observing the distribution of riverine DOM on the SAB shelf in high spatial resolution and by using remote sensing methods, a crucial step for quantifying shelf-slope exchange and the fate of terrigenous DOM in shelf seas.

Medeiros, P.M., Seidel, M., Dittmar, T., Whitman, W.B. and Moran, M.A. 2015. Drought-induced variability in dissolved organic matter composition in a marsh-dominated estuary. Geophysical Research Letters. 42:6446-6453. (DOI: 10.1002/2015GL064653)

Abstract
The composition of dissolved organic matter (DOM) in an estuary characterized by extensive salt marsh vegetation was investigated at the molecular level using ultrahigh-resolution mass spectrometry and stable carbon isotope analyses. Samples from multiple seasons covered different hydrological regimes, including anomalously low-discharge conditions. The untargeted approach used allowed for identifying the DOM molecular signatures associated with different DOM sources in the estuary. DOM composition was strongly modulated by river discharge at monthly scales, with high river flow leading to significant increases in the terrigenous signature of the DOM throughout the estuary. During a severe/exceptional drought, estuarine DOM was imprinted with a distinct signature of marsh-derived compounds. The frequency of occurrence of anomalously low-discharge conditions seems to have increased over the last decades. If predictions of anthropogenically driven changes in hydroclimate are confirmed, they will likely be accompanied by changes in DOM composition in estuaries at multidecadal time scales.

Medeiros, P.M., Seidel, M., Gifford, S., Ballantyne, F., Dittmar, T., Whitman, W.B. and Moran, M.A. 2017. Microbially-mediated transformations of estuarine dissolved organic matter. Special Issue: Integrative Research on Organic Matter Cycling Across Aquatic Gradients. Frontiers in Marine Science. 4(69). (DOI: 10.3389/fmars.2017.00069)

Abstract
Microbially-mediated transformations of dissolved organic matter (DOM) in a marsh-dominated estuarine system were investigated at the molecular level using ultrahigh resolution mass spectrometry. In addition to observing spatial and temporal variability in DOM sources in the estuary, multiple incubations with endogenous microorganisms identified the influence of DOM composition on biodegradation. A clear microbial preference for degradation of compounds associated with marine DOM relative to those of terrestrial origin was observed, resulting in an overall shift of the remaining DOM toward a stronger terrigenous signature. During short, 1-day long incubations of samples rich in marine DOM, the molecular formulae that were enriched had slightly smaller mass (20–30 Da) and number of carbon atoms compared to the molecular formulae that were depleted. Over longer time scales (70 days), the mean differences in molecular mass between formulae that were depleted and enriched were substantially larger (~270 Da). The differences in elemental composition over daily time scales were consistent with transformations in functional groups; over longer time scales, the differences in elemental composition may be related to progressive transformations of functional groups of intermediate products and/or other reactions. Our results infused new data toward the understanding of DOM processing by bacterioplankton in estuarine systems.

Medeiros, P.M., Seidel, M., Niggemann, J., Spencer, R.G., Hernes, P.J., Yager, P., Miller, W., Dittmar, T. and Hansell, D.A. 2016. A novel molecular approach for tracing terrigenous dissolved organic matter into the deep ocean. Global Biogeochemical Cycles. 30(5):689–699. (DOI: 10.1002/2015GB005320)

Abstract
Marine dissolved organic matter (DOM) contains one of the largest exchangeable organic carbon pools on Earth. Riverine input represents an important source of DOM to the oceans, yet much remains to be learned about the fate of the DOM linking terrestrial to oceanic carbon cycles through rivers at the global scale. Here we use ultrahigh-resolution mass spectrometry to identify 184 molecular formulae that are indicators of riverine inputs (referred to as t-Peaks) and to track their distribution in the deep North Atlantic and North Pacific Oceans. The t-Peaks were found to be enriched in the Amazon River, to be highly correlated with known tracers of terrigenous input, and to be observed in all samples from four different rivers characterized by vastly different landscapes and vegetation coverage spanning equatorial (Amazon and Congo), subtropical (Altamaha), and Arctic (Kolyma) regions. Their distribution reveals that terrigenous organic matter is injected into the deep ocean by the global meridional overturning circulation, indicating that a fraction of the terrigenous DOM introduced by rivers contributes to the DOM pool observed in the deep ocean and to the storage of terrigenous organic carbon. This novel molecular approach can be used to further constrain the transfer of DOM from land to sea, especially considering that Fourier transform ion cyclotron resonance mass spectrometer analysis is becoming increasingly frequent in studies characterizing the molecular composition of DOM in lakes, rivers, and the ocean.

Meile, C., Porubsky, W.P., Walker, R.L. and Payne, K. 2009. Natural Attenuation Of Nitrogen Loading From Septic Effluents: Spatial And Environmental Controls. Water Research. 44(5):1399-1408. (DOI: 10.1016/j.watres.2009.11.019)

Abstract
We assess the role of septic systems as potential nitrogen (N) sources to coastal open water bodies. To quantify the potential role of septic tanks, we document the distribution pattern and functionality of septic tanks in McIntosh County in Georgia, USA, and examine factors governing the mitigation of septic N loading in coastal groundwater. Employing a field calibrated 2D variable-density reaction-transport model, we focus on the role of setback distance of a leaky septic source from the receiving surface waters, on transport and biogeochemical characteristics of the subsurface environment, and on leachate composition and reactivity. We conclude that the removal of bioavailable nitrogen via denitrification may be increased by increasing the septic system setback distance, in particular in brackish and saline coastal settings where sulfide produced in sulfate reduction can limit N2 production.

Miklesh, D.M. and Meile, C. 2018. Controls on porewater salinity in a Southeastern salt marsh. PeerJ. 6:e5911. (DOI: 10.7717/peerj.5911)

Abstract
In coastal marsh ecosystems, porewater salinity strongly affects vegetation distribution and productivity. To simulate marsh porewater salinity, an integrated, spatially explicit model was developed, accounting for tidal inundation, evaporation, and precipitation, as well as lateral and vertical exchanges in both surface waters and the subsurface. It was applied to the Duplin River marsh, Sapelo Island, USA, over a 3-year period, which covered both drought and wet conditions. Simulated porewater salinity in the low and high marsh correlated with Duplin River salinity, withevapotranspiration and precipitation leading to substantial variations in porewater salinities across seasons, in particular in the high marsh. The model revealed substantial interannual variability in marsh soil conditions, and—due to its processbased approach linked to external forcings—can be used to explore effects of sea level rise and changes in hydrological forcings on marsh soil conditions.

Moore, W.S., Blanton, J.O. and Joye, S.B. 2006. Estimates of flushing times, submarine groundwater discharge, and nutrient fluxes to Okatee Estuary, South Carolina. Journal of Geophysical Research. 111:C09006. (DOI: 10.1029/2005JC003041)

Abstract
A physical model based on determining the fraction of the tidal prism that returns to the estuary on the next high tide is used to estimate the flushing time of the Okatee River estuary. The return flow factor (b) of 0.81 yields a flushing time of 2 days. A mass balance model of 228Ra and salinity is also used to estimate b. This model yields an average b = 0.79, virtually the same as the physical model. A third model based on the decay of 224Ra relative to 228Ra is used to determine the apparent age of water in the estuary. These ages range from 1.6 to 5 days, with an average of 3.4 days. These three independent estimates are in remarkably close agreement, certainly within the error of each estimate. We use these residence times to develop a mass balance model for the radium isotopes in the Okatee estuary. We consider decay, mixing, sedimentary input, river input, and submarine groundwater discharge (SGD). The major loss term for each isotope is mixing with water in Port Royal Sound; the major input for each isotope is SGD. At steady state these terms must balance. Knowing the water age and the radium isotope composition of groundwater entering the Okatee allows us to estimate an average SGD flux of 1 m3/s. The SGD flux is a factor of 3–4 greater during the summer relative to the winter. This SGD supplies a considerable quantity of nutrients and carbon into the Okatee system.

Moore, W.S., Krest, J., Taylor, G., Roggenstein, E., Joye, S.B. and Lee, R.Y. 2002. Thermal evidence of water exchange through a coastal aquifer: implications for nutrient fluxes. Geophysical Research Letters. 29(14):1704. (DOI: 10.1029/2002GL014923)

Abstract
We report the discovery of a semi-confined, high permeability zone (HPZ) 2 meters below the sea bed where exchanges between coastal aquifers and the ocean occur. A temperature probe placed in the HPZ recorded a 1°C semidiurnal cycle. The cycle was in phase with the tide, indicating tidal pumping was driving water exchange through the HPZ. We use these temperature variations to quantify water exchange between the HPZ and the ocean. Water in the HPZ is enriched in nutrients and radium; both total dissolved nitrogen and phosphorus correlate strongly with dissolved 226Ra. We use these correlations and previously quantified subterranean fluxes of 226Ra to demonstrate that this system may be a significant source of nutrients to the coastal ocean.

Mou, X., Hodson, R.E. and Moran, M.A. 2007. Bacterioplankton assemblages transforming dissolved organic compounds in coastal seawater. Environmental Microbiology. 9:2025–2037. (DOI: 10.1111/j.1462-2920.2007.01318)

Abstract
To characterize bacterioplankton functional assemblages that transform specific components of the coastal seawater dissolved organic carbon (DOC) pool, bromodeoxyuridine (BrdU) was used to label the bacterioplankton cells that were active following addition of single-DOC model compounds: two organic osmolytes [dimethylsulfoniopropionate (DMSP) and glycine betaine (GlyB)] and two aromatic monomers [para-hydroxybenzoic acid (pHBA) and vanillic acid (VanA)]. Bacterial populations were analysed based on in situ fluorescent immunodetection of BrdU incorporation followed by fluorescence-activated cell sorting (FACS). Sorted cells were then characterized by 16S rDNA-based analysis. Populations with high BrdU incorporation level (HI) developed within 8 h of introduction of 100 nM model compound. Terminal restriction fragment length polymorphisms (T-RFLP) analysis indicated that the HI populations in all four amendments were composed of bacteria from the same major taxa (phylum and subphylum levels), but the relative abundance of each differed. High-resolution clone libraries (each containing ~200 clones) showed that the HI populations in the GlyB and VanA amendments consisted of both metabolic generalists and specialists within the l-Proteobacteria (mainly members of the Roseobacter clade), ř-Proteobacteria and d-Proteobacteria (mainly members of Altermonadaceae, Chromatiaceae, Oceanospirillaceae and Pseudomonadaceae). The presence of members of OM60/241, OM185, SAR11, SAR86 and SAR116 in the HI populations indicated that members of these groups can assimilate the model DOC compounds, providing some of the first glimpses into heterotrophy by members of these poorly understood environmental clusters.

Mou, X., Moran, M.A., Stepansuskas, R., Gonzalez, J.M. and Hodson, R.E. 2005. Flow-cytometric cell sorting and subsequent molecular analyses for culture-independent identification of bacterioplankton involved in dimethylsulfoniopropionate transformations. Applied and Environmental Microbiology. 71:1405-1416. (DOI: 10.1128/AEM.71.3.1405–1416.2005)

Abstract
Marine bacterioplankton transform dimethylsulfoniopropionate (DMSP) into the biogeochemically important and climatically active gas dimethylsulfide. In order to identify specific bacterial taxa mediating DMSP processing in a natural marine ecosystem, we amended water samples from a southeastern U.S. salt marsh with 20 uM DMSP and tracked community shifts with flow cytometry (FCM) coupled to 16S rRNA gene analyses. In two out of four seasons studied, DMSP amendments induced the formation of distinct bacterioplankton populations with elevated nucleic acid (NA) content within 24 h, indicative of cells actively utilizing DMSP. The 16S rRNA genes of the cells with and without elevated NA content were analyzed following cell sorting and PCR amplification with sequencing and terminal restriction fragment length polymorphism approaches. Compared to cells in the control FCM populations, bacteria with elevated NA content in the presence of DMSP were relatively enriched in taxa related to Loktanella, Oceanicola, and Sulfitobacter (Roseobacter lineage, alpha-Proteobacteria); Caulobacter (alpha-Proteobacteria); and Brachymonas and Xenophilus (beta-Proteobacteria) in the May-02 sample and to Ketogulonicigenium (Roseobacter lineage, alpha-Proteobacteria) and novel gamma-Proteobacteria in the Sept-02 sample. Our study suggests that diverse bacterioplankton participate in the metabolism of DMSP in coastal marine systems and that their relative importance varies temporally.

Napora, K., Cherkinsky, A., Speakman, R.J., Thompson, V.D., Horan, R. and Jacobs, C. 2019. Radiocarbon Pretreatment Comparisons of Bald Cypress (Taxodium distichum) Wood Samples from a Massive Buried Deposit on the Georgia Coast, USA. Radiocarbon.

Abstract
We sampled individual growth rings from three ancient remnant bald cypress (Taxodium distichum) trees from a massive buried deposit at the mouth of the Altamaha River on the Georgia Coast to determine the best technique for radiocarbon (14C) dating pretreatment. The results of our comparison of traditional ABA pretreatment and holocellulose and α-cellulose fractions show no significant differences among the pretreatments (<1 sigma) thereby suggesting that ABA pretreatment will prove sufficient for the development of a high-resolution 14C tree-ring chronology based on these ancient bald cypresses which will indicate whether the U.S. Southeast is subject to a regional radiocarbon offset.

Newell, S.Y. 2001. Fungal biomass and productivity in standing-decaying leaves of black needlerush. Marine and Freshwater Research. 52:249-255.

Abstract
Ascomycetous fungal decomposers generate the major part of the microbial biomass on and in standing naturally decaying shoots for one (smooth cordgrass, Spartina alterniflora) of the two major ramet-forming marsh plants of the south-eastern USA. Evidence from frequency of occurrence of sexual structures (ascomata) in the second major ramet-forming marsh plant (black needlerush, Juncus roemerianus) suggests that fungi are major secondary producers in the needlerush decomposition system also. To test this, samples of needlerush blades at three stages of decay were collected seasonally for three years. Average living-fungal standing crop (as ergosterol) of needlerush blades (254 ug g^–1 organic mass of decay system) was ~65% of a comparable average for smooth cordgrass, but fungal mass was equally active between the two species (near 30 pmol acetate incorporated into ergosterol ug^–1 ergosterol h^–1). Although maximum living-fungal crop for needlerush was found in winter, and in winter and spring for smooth cordgrass, in many other respects, patterns of change in needlerush fungal variables were quite different from those for smooth cordgrass. For example, living-fungal standing crop rose 1.5-fold with decay stage for needlerush, but was constant for cordgrass, perhaps because of lesser mycophagous activity and lesser competition from bacterioplankton associated with tidal flooding in the high-marsh, needlerush zones.

Newell, S.Y. 2001. Multiyear patterns of fungal biomass dynamics and productivity within naturally decaying smooth-cordgrass shoots. Limnology & Oceanography. 46:573-583.

Abstract
Ascomycetous fungi are predominant secondary microbial producers of the smooth cordgrass (Spartina alterni-flora) shoot decay system. A 3-yr examination of concentrations of living fungal mass (as ergosterol content) in naturally decaying cordgrass, and of instantaneous rates of cordgrass–fungal production (as rates of incorporation of radiolabeled acetate into ergosterol at a standard temperature of 20°C), was conducted in three salt-marsh watersheds of Sapelo Island. Though the years of study were climatologically different (e.g., rainfall ranging over a factor ~2), ergosterol content of decaying leaves was not different from year to year, with a grand mean of 371 mg ergosterol g^-1 organic mass of decaying system, and there was little difference among yearly average fungal productivities (range = 155–217 ug fungal organic mass g^-1 system organic mass h^-1 for autumn–spring data). Significant differences in ergosterol content of decaying leaves were found among marsh watersheds, probably due to differences in nitrogen (but not phosphorus) availability, but these were not large (maximum 1.3-fold for multiseasonal data), and differences were not found among marsh subsites (short to tall shoot) nor, for the most part, among types or parts of decaying leaves. Season of sampling, however, had a large effect upon fungal biomass and fungal productivity: average ergosterol contents were significantly higher in winter and spring (e.g., 416–554 ug g^-1 organic mass of decaying blades) than in summer or autumn (<310 ug g^-1). Among the potential reasons for this unexpected pattern of seasonality might be (1) greater access of mycophagous invertebrates and/or bacterial competitors due to higher tides and lower elevation of leaves in late summer and fall, and (2) leaching of leaf digestate during periods of high rainfall and high spring tides. Significant correlations were found between ergosterol content of decaying leaves and mean tidal height for the 3 months before sampling (r = -0.77) and for fungal productivities and 3-month rainfall (r = -0.62). Grazing of decaying leaves by salt-marsh periwinkles over the range of snail densities of the study sites (0–85 m^-2) gave no clear evidence of depression of fungal biomass or repression of fungal activity, contrary to previous findings for higher snail densities. The calculated seasonal change in living fungal percentage of decaying leaves was from ~6 (summer–autumn) to 9% (winter–spring), and in 6-month fungal production, the change was from 101 to 434 g organic fungal mass m^-2 marsh surface.

Newell, S.Y. 2001. Spore-expulsion rates and extents of blade occupation by ascomycetes of the smooth-cordgrass standing-decay system. Botanica Marina. 44:277-285.

Abstract
Species of ascomycetes are the principal microbial secondary producers in standing-decaying shoots of smooth cordgrass (Spartina alterniflora), the foremost and highly productive grass of saltmarshes of the eastern USA. Rates of expulsion of ascospores from wet, standing-decaying leaves of S. alterniflora were measured in spore-capture chambers seasonally, over a 3-year period. Extents of occupation of decaying leaves were determined by measuring sizes of characteristic patches associated with different species or species groups. Patches of leaf blades not occupied by at least one of the ascomycetes of the smooth-cordgrass ascomycete community occupied less than 0.2% of leaf abaxial area. Patches of the 'black-peppered' appearance (containing ascomata of one or more of the following: Phaeosphaeria spartinicola, Mycosphaerella sp. 2, Phaeosphaeria halima) occupied 91 to 98% of abaxial leaf area for mid-shoot blades at subsites containing tall and intermediate-height shoots. At short-shoot sites, 'peppered' patches occupied 53% of leaf area, due to higher levels of periwinkle grazing at short-shoot sites; size of 'peppered' patches was negatively correlated with extent of severe invertebrate grazing of leaves (r = -0.87). Blackened patches (containing ascomata of Buergenerula spartinae) had an overall average occupation percentage of 17% of leaf area, and the percentage was not significantly affected by periwinkle grazing (r = -0.13). Attached decaying leaf blades low on shoots and leaf sheaths expelled few spores (< 30% of the average for mid-shoot and upper-shoot blades), and for sheaths, B. spartinae was apparently the principal ascomycete releasing spores. For mid-shoot and uppershoot decaying blades, mean total ascospore-expulsion rate ranged from 14 to 131 spores mm^-2 leaf abaxial surface (72 h)^-1, depending on marsh watershed and season. Higher percentages of expelled ascospores for Phaeosphaeria spartinicola were found for autumn and winter (52 to 62% of spores), but for Mycosphaerella sp. 2, peak seasons were summer and spring (42 to 54% of spores). Percentages of ascospores for these two species were uniform over years, marsh watersheds, and tall- to short-shoot marsh subsites, whereas Phaeosphaeria halima exhibited a high degree of spatiotemporal patchiness. Because the ascospore-capture method used does not measure total ascospore release, only minimum values could be calculated for ascospore output m^-2 marsh. Calculated minimum rates of total ascospore expulsion for mid-shoot plus upper-shoot blades were 1.3 million spores m^-2 marsh h^-1 of blade wetness, 5.9 billion spores m^-2 marsh yr^-1, and 7.5 g organic mass m^-2 yr^-1, amounting to 4.5% of total annual fungal production within these blades.

Newell, S.Y. 2003. Fungal content and activities in standing-decaying leaf blades of plants of the Georgia Coastal Ecosystems research area. Aquatic Microbial Ecology. 32:95-103.

Abstract
Change in salinity, including expansion or contraction of salt- and freshwater marshes, due to altered river outflow may influence a variety of ecosystem processes, and the literature suggests that fungal activity in standing-decaying blades of macrophytes may be lower in freshwater marshes than in saltmarshes. I measured living-fungal mass (as ergosterol), rate of carbon-dioxide evolution, and rate of fungal membrane synthesis (acetate incorporation into ergosterol) for standing-decaying blades from a series of macrophytes, including saltmarsh cordgrass in both saline and fresher-water sites. Three terrestrial plants with prominent standing-decaying leaf blades were included for comparison. Species involved were: Spartina alterniflora, Spartina cynosuroides, Zizaniopsis miliacea, Typha angustifolia, Sabal palmetto, Uniola paniculata, and Panicum amarum. Although there was no difference in fungal content of S. alterniflora blades from saltier and fresher sites, there was a significant trend downwards (from >500 to <250 µg ergosterol g-1 system organic mass) in mean content of living-fungal mass moving from saltmarsh-adapted toward freshwater-adapted plants, and two of three terrestrial plants were also low (ca. 100 µg g-1). The activity measurements (CO2, acetate incorporation) revealed an opposite pattern: blades from fresher-water plants had higher activities per unit living-fungal mass (range of about 4-fold for mean rate of acetate incorporation per unit ergosterol), and lower CO2 release per unit fungal membrane synthesis, than did more saline-adapted plants. It is proposed that this is perhaps largely a consequence of the microstructure (lignification, cuticular hydrophobicity) of the blades of the fresher-water plants (and two of the terrestrial plants) limiting duration of fungal activity. Upon thorough wetting, such as eventually occurs when blades move to the marsh-sediment surface, fungi within the fresher-water blades would be permitted to grow quickly, which would explain reported

Nifong, J.C. and Silliman, B.R. 2013. Impacts of a large-bodied, apex predator (Alligator mississippiensis Daudin 1801) on salt marsh food webs. Journal of Experimental Marine Biology and Ecology. 440(2013):185-191. (DOI: 10.1016/j.jembe.2013.01.002)

Abstract
Large-bodied apex predators (e.g., sharks, wolves, crocodilians) are believed to regulate food web structure and drive ecosystem processes, but there remains relatively little experimental evidence. Here we use field surveys and a mesocosm experiment to evaluate the cascading effects of an apex predator (American alligator) on a salt marsh food web. Consistent with previous studies (n = 10), field surveys revealed blue crabs (Callinectes sapidus Rathbun 1896), an important marsh mesopredator, were a frequent component of estuarine-occurring alligators' diet (mean ± SD, 47 ± 20%, n = 1384). In mesocosms, we examined potential consequences of this interaction in a simplified salt marsh community. We experimentally isolated alligator effects on the abundance (consumptive effect) and behavior (non-consumptive effect) of blue crabs and on blue crab consumption of plant-grazing snails and ribbed mussels. Alligators reduced blue crab abundance by ~ 40% over 3 days and induced behavioral changes, resulting in decreased foraging activity and increased refuge use by blue crabs. The combined effects of reduced crab abundance and altered behavior translated into increased survival of both a keystone grazer (snails) and a mutualist (mussels) within the salt marsh food web. Our findings experimentally demonstrate that a large-bodied, apex predator has the potential to 1) generate a trophic cascade, 2) elicit behavioral changes (i.e., non-consumptive effects) in mesopredator prey, and 3) indirectly affect the potential for both grazing and mutualism to occur in this food chain. Our results generate testable hypotheses regarding the broad-scale effects of alligator presence and top-down forcing in salt marsh ecosystems.

Nifong, J.C. and Silliman, B.R. 2017. Abiotic factors influence the dynamics of marine habitat use by a highly mobile “freshwater” top predator. Hydrobiologia. 802(1):155-174. (DOI: 10.1007/s10750-017-3255-7)

Abstract
Cross-ecosystem movements of mobile consumers are a primary mechanism by which energy and nutrients are exchanged between disparate ecosystems. While factors influencing variation in bottom–up subsidies between ecosystems have been well studied, much less is known regarding how biotic and abiotic factors influence the dynamics of mobile consumer-driven connectivity. In a literature survey, we found only 14% of studies examined factors contributing to variation in cross-ecosystem marine foraging by freshwater-adapted consumers. Here, we examine the relationships between abiotic factors and cross-ecosystem movements of a highly mobile freshwater-adapted top predator, Alligator mississippiensis (American alligator). As alligators lack physiological adaptations to survive in marine environments, we predict this linkage would be affected by factors that modify the ability to cope with high salinities. Our results reveal that multiple abiotic factors (e.g., relative humidity, temperature, total precipitation) are key explanatory variables of the duration of cross-ecosystem foraging trips by alligators, and that the absence of salt glands does not preclude them from performing long forays into marine environments. More broadly, our results expand our understanding of mobile consumer-driven ecosystem connectivity at the land–sea interface by demonstrating connectivity is highest when physical stressors are relaxed, and access to and availability of resources are maximized.

Nifong, J.C., Layman, C. and Silliman, B.R. 2015. Size, sex, and individual-level behavior drive intra-population variation in cross-ecosystem foraging of a top-predator. Journal of Animal Ecology. (DOI: 10.1111/1365-2656.12306)

Abstract
Large-bodied top-predators exert pervasive top-down effects within food webs, thereby affecting ecosystem structure and function. Effects of these consumers are propagated by a range of mechanisms including consumptive and non-consumptive interactions with prey, and the translocation of nutrients, among others (Terborgh et al. 2010; Rosenblatt et al. 2013a). Large-bodied predators are often highly mobile and can link spatially distinct habitats while acquiring prey, increasing connectivity between ecosystems. Predator-driven linkages have important ecological implications; for instance, these linkages are hypothesized to stabilize food webs by dampening population oscillation cycles (e.g. McCauley, Wilson & de Roos 1996; Loreau & Holt 2004; McCann, Rasmussen & Umbanhowar 2005). An understanding of factors regulating the occurrence and strength of predator-driven connectivity can inform predictions of when and where these species may influence structure and function of interconnected communities and ecosystems (e.g. Huxel & McCann 1998; Leroux & Loreau 2008; Rooney, McCann & Moore 2008).

Nifong, J.C., Lowers, R., Silliman, B.R., Abernathy, K. and Marshall, G. 2013. Attachment and deployment of remote video/audio recording devices (Crittercam) on wild American alligators (Alligator mississippiensis Duadin 1801). Herpetological Review. 44(2):243-247.

Abstract
Historically, researchers have used direct observation, often with the assistance of specialized equipment (e.g., binoculars, telescopes, remote video/audio recorders), to document animal behavior and ecology (Altmann 1974). However, these observerbased techniques typically cause disturbance to animals via presence of observers or equipment, are limited in the data that can be collected (e.g., field of view, magnification), and often occur over short temporal scales, all of which restrict the inferences that can be gleaned from the data (Marsh and Hanlon 2004; Samuel et al. 1987). Documenting the behavior of aquatic species, such as crocodilians, presents additional complications because the majority of their interactions occur below the water’s surface where direct observation can be even more challenging (Dickens et al. 2011). To overcome these limitations and increase the quality and quantity of observational data, researchers have utilized technological advances to develop devices that can be attached to animals and are capable of collecting video and audio data from the animal’s point-of-view. Collectively known as “animalborne imagery,” this field has flourished in the past 20 years, inpart due to the success of the National Geographic Remote Imaging (NGRI) Crittercam program (Marshall 1998). To date, their animal-borne imaging systems have been used to study the behavior of over 60 species spanning a wide range including aquatic vertebrates and invertebrates, such as large sharks, sea turtles, and Humboldt squid, as well as terrestrial species such as lions, bears, and various species of birds (Marshall, unpubl. data). Crittercam, in addition to other animal-borne imaging systems, has revolutionized the field of animal behavior and ecology by permitting the observation of novel natural history characteristics, such as cryptic foraging behaviors or subtle species interactions, and by expanding the range of response variables available for ecological studies, such as diving, foraging, and prey capture success rates (Moll et al. 2007).

Nifong, J.C., Nifong, R., Silliman, B.R., Lowers, R., Guillette, L., Ferguson, M., Welsh, M., Abernathy, K. and Marshall, G. 2014. Animal-borne imaging reveals novel insights into the foraging behaviors and diel activity of a large-bodied apex predator, the American alligator (Alligator mississippiensis). PLOS One. 9(1). (DOI: 10.1371/journal.pone.0083953)

Abstract
Large-bodied, top- and apex predators (e.g., crocodilians, sharks, wolves, killer whales) can exert strong top-down effects within ecological communities through their interactions with prey. Due to inherent difficulties while studying the behavior of these often dangerous predatory species, relatively little is known regarding their feeding behaviors and activity patterns, information that is essential to understanding their role in regulating food web dynamics and ecological processes. Here we use animal-borne imaging systems (Crittercam) to study the foraging behavior and activity patterns of a cryptic, large-bodied predator, the American alligator (Alligator mississippiensis) in two estuaries of coastal Florida, USA. Using retrieved video data we examine the variation in foraging behaviors and activity patterns due to abiotic factors. We found the frequency of prey-attacks (mean = 0.49 prey attacks/hour) as well as the probability of prey-capture success (mean = 0.52 per attack) were significantly affected by time of day. Alligators attempted to capture prey most frequently during the night. Probability of prey-capture success per attack was highest during morning hours and sequentially lower during day, night, and sunset, respectively. Position in the water column also significantly affected prey-capture success, as individuals’ experienced two-fold greater success when attacking prey while submerged. These estimates are the first for wild adult American alligators and one of the few examples for any crocodilian species worldwide. More broadly, these results reveal that our understandings of crocodilian foraging behaviors are biased due to previous studies containing limited observations of cryptic and nocturnal foraging interactions. Our results can be used to inform greater understanding regarding the top-down effects of American alligators in estuarine food webs. Additionally, our results highlight the importance and power of using animal-borne imaging when studying the behavior of elusive large-bodied, apex predators, as it provides critical insights into their trophic and behavioral interactions.

Nifong, J.C., Rosenblatt, A.E., Johnson, N., Barichivich, W., Silliman, B.R. and Heithaus, M. 2012. American Alligators Digestion Rate of Blue Crabs and its Implications for Stomach Contents Analysis. Copeia. 2012(3):419-423. (DOI: 10.1643/CE-11-177)

Abstract
Stomach contents analysis (SCA) provides a snap-shot observation of a consumer's diet. Interpretation of SCA data can be complicated by many factors, including variation in gastric residence times and digestion rates among prey taxa. Although some SCA methods are reported to efficiently remove all stomach contents, the effectiveness of these techniques has rarely been tested for large irregular shaped prey with hard exoskeletons. We used a controlled feeding trial to estimate gastric residency time and decomposition rate of a large crustacean prey item, the Blue Crab (Callinectes sapidus), which is consumed by American Alligators (Alligator mississippiensis), an abundant apex predator in coastal habitats of the southeastern United States. The decomposition rate of C. sapidus in the stomachs of A. mississippiensis followed a predictable pattern, and some crab pieces remained in stomachs for at least 14 days. We also found that certain portions of C. sapidus were prone to becoming caught within the stomach or esophagus, meaning not all crab parts are consistently recovered using gastric lavage techniques. However, because the state of decomposition of crabs was predictable, it is possible to estimate time since consumption for crabs recovered from wild alligators. This information, coupled with a detailed understanding of crab distributions and alligator movement tactics could help elucidate patterns of cross-ecosystem foraging by the American Alligator in coastal habitats. © 2012 by the American Society of Ichthyologists and Herpetologists.

O'Connell, J. and Alber, M. 2016. A smart classifier for extracting environmental data from digital image time-series: Applications for PhenoCam data in a tidal salt marsh. Environmental Modelling & Software. 84:134-139. (DOI: 10.1016/j.envsoft.2016.06.025)

Abstract
PhenoCams are part of a national network of automated digital cameras used to assess vegetation phenology transitions. Effectively analyzing PhenoCam time-series involves eliminating scenes with poor solar illumination or high cover of non-target objects such as water. We created a smart classifier to process images from the “GCESapelo” PhenoCam, which photographs a regularly-flooded salt marsh. The smart classifier, written in R, assigns pixels to target (vegetation) and non-target (water, shadows, fog and clouds) classes, allowing automated identification of optimal scenes for evaluating phenology. When compared to hand-classified validation images, the smart classifier identified scenes with optimal vegetation cover with 96% accuracy and other object classes with accuracies ranging from 86 to 100%. Accuracy for estimating object percent cover ranged from 74 to 100%. Pixel-classification with the smart classifier outperformed previous approaches (i.e. indices based on average color content within ROIs) and reduced variance in phenology index time-series. It can be readily adapted for other applications.

O'Connell, J., Alber, M. and Pennings, S.C. 2019. Microspatial differences in soil temperature cause phenology change on par with long-term climate warming in salt marshes. Ecosystems. (DOI: https://doi.org/10.1007/s10021-019-00418-1)

Abstract
Phenology studies mostly focus on variation across time or landscapes. However, phenology can vary at fine spatial scales, and these differences may be as important as long-term change from climate warming. We used high-frequency ‘‘PhenoCam’’ data to examine phenology of Spartina alterniflora, afoundation species native to salt marshes on the US East and Gulf coasts, and a common colonizer elsewhere. We examined phenology across three microhabitats from 2013 to 2017 and used this information to create the first spring green-up model for S. alterniflora. We then compared modern spatial variation to that exhibited over a 60-year climate record. Marsh interior plants initiated spring growth 17 days earlier than channel edge plants and spent 35 days more in the green-up phenophase and 25 days less in the maturity phenophase. The start of green-up varied by 17 days among 3 years. The best spring green-up model was based on winter soil total growing degree days. Across microhabitats, spring green-up differences were caused by small elevation changes (15 cm) that drove soil temperature variation of 0.8C. Preliminary evidence indicated that high winter belowground biomass depletion triggered early green-up. Long-term change was similar: winter soil temperatures warmed 1.7 ± 0.3C since 1958, and green-up advanced 11 ± 6 days, whereas contemporary microhabitat differences were 17 ± 4 days. Incorporating local spatial variation into plant phenology models may provide an early warning of climate vulnerability and improve understanding of ecosystem-scale productivity. Microscale phenology variation likely exists in other systems and has been unappreciated.

O'Connell, J., Mishra, D., Cotten, D.L., Wang, L. and Alber, M. 2017. 'The Tidal Marsh Inundation Index (TMII): An inundation filter to flag flooded pixels and improve MODIS tidal marsh vegetation time-series analysis '. Remote Sensing of the Environment. 201(November 2017):34-46. (DOI: 10.1016/j.rse.2017.08.008)

Abstract
Remote sensing in tidal marshes can provide regional assessments of wetland extent, phenology, primary production, and carbon sequestration. However, periodic tidal flooding reduces spectral reflectance, especially in the near and short-wave infrared wavelengths. Consequently, marsh vegetation time-series products that lack tidal filtering, such as those provided by MODIS (Moderate Resolution Imaging Spectroradiometer), may not reflect true vegetation trends. We created a new Tidal Marsh Inundation Index (TMII) for processing daily 500-m MODIS surface reflectance data and calibrated it with a Spartina alterniflora salt marsh pixel on Sapelo Island, GA. Ground-truth data for TMII was extracted from a PhenoCam, which collected high frequency digital photography of the TMII calibration pixel. To identify the best wavelengths to include in the TMII, we compared goodness of fit metrics from generalized linear models (GLMs). Predictors for these GLMs included suites of normalized difference indices from the literature as well as other band combinations. We also explored including a phenology parameter that could scale TMII relative to vegetation development. Ultimately, TMII was based on the normalized difference of green and shortwave infrared reflectance in combination with a phenology parameter composed of the moving average of the normalized difference of near infrared and shortwave infrared reflectance. This final index allowed a single optimized decision boundary to identify flooding across the annual growth cycle. When compared to ground-truth data from the PhenoCam, the TMII classified flooded conditions with 67–82% and dry conditions with 75–81% accuracy, respectively, across training, testing and validation datasets. We applied TMII to new S. alterniflora marsh MODIS pixels on Sapelo Island, GA as well as on Plum Island, MA. For these new pixels, TMII classified marsh flooding with 77–80% overall accuracy. We also demonstrated how users can apply TMII filtering in a MODIS workflow to create vegetation time-series composites within S. alterniflora, Spartina patens and Juncus roemerianus marshes. We showed how a new user can validate and optimize TMII in their application, either by comparing it to inundation data or by validating the filtered vegetation time series against field data. We also compared TMII-filtered composites to the existing MODIS MOD13 16-d Normalized Difference Vegetation Index (NDVI) product. TMII-filtered composites generated less noisy time-series that fit field data better than MOD13. TMII filtering was most important on Sapelo Island, where the tide range was high and vegetation was sparse. Results were less dramatic when TMII was applied to different marsh species within the Gulf Coast sites with lower tidal ranges, but TMII-filtering still improved vegetation time series. Thus, preprocessing MODIS imagery with the TMII effectively identified most inundated pixels. The TMII represents a step forward for wetland remote sensing that will be useful for improved estimation of phenology, biomass and carbon storage in coastal marshes.

O'Donnell, J. and Schalles, J.F. 2016. Examination of Abiotic Drivers and Their Influence on Spartina alterniflora Biomass over a Twenty-Eight Year Period Using Landsat 5 TM Satellite Imagery of the Central Georgia Coast. Special Issue: Remote Sensing in Coastal Environments. Remote Sensing. 8(6):22. (DOI: 10.3390/rs8060477)

Abstract
We examined the influence of abiotic drivers on inter-annual and phenological patterns of aboveground biomass for Marsh Cordgrass, Spartina alterniflora, on the Central Georgia Coast. The linkages between drivers and plant response via soil edaphic factors are captured in our graphical conceptual model. We used geospatial techniques to scale up in situ measurements of aboveground S. alterniflora biomass to landscape level estimates using 294 Landsat 5 TM scenes acquired between 1984 and 2011. For each scene we extracted data from the same 63 sampling polygons, containing 1222 pixels covering about 1.1 million m2. Using univariate and multiple regression tests, we compared Landsat derived biomass estimates for three S. alterniflora size classes against a suite of abiotic drivers. River discharge, total precipitation, minimum temperature, and mean sea level had positive relationships with and best explained biomass for all dates. Additional results, using seasonally binned data, indicated biomass was responsive to changing combinations of variables across the seasons. Our 28-year analysis revealed aboveground biomass declines of 33%, 35%, and 39% for S. alterniflora tall, medium, and short size classes, respectively. This decline correlated with drought frequency and severity trends and coincided with marsh die-backs events and increased snail herbivory in the second half of the study period.

Ogburn, M.B. and Alber, M. 2006. An Investigation of Salt Marsh Dieback in Georgia using Field Transplants. Estuaries and Coasts. 29(1):54-62

Abstract
In 2001 and 2002, Georgia salt marshes experienced a dieback event that affected more than 800 ha throughout the coastal zone. The dieback event was unprecedented in the state and affected both Spartina alterniflora and Juncus roemerianus. A transplant study was conducted from May to October 2003 to determine if healthy plants could survive in dieback areas. Transplants were carried out at two locations on the Georgia coast in areas of S. alterniflora dieback along the banks of tidal creeks, in an area of S. alterniflora dieback in the mid marsh, and in a J. roemerianus dieback area in the mid marsh. Transplant survival was nearly 100% and growth (measured as increases in the height of the 5 tallest stems and the number of stems per experimental pot) was observed in both healthy (control) and dieback areas. J. romerianus grew more slowly than S. alterniflora, with no observed increase in stem height and an average 38% increase in stem density as compared to an average 57% increase in stem height and 137% increase in stem density in S. alterniflora. Differences in growth were inconsistent but in most cases no significant differences were observed between healthy and dieback areas. Soil characteristics measured over the course of the experiment were generally comparable between healthy and dieback areas (redox potential averaged 69 ± 123 (s.d.) across all observations at all sites, pH averaged 6.7 ± 0.3, and salinity averaged 24.9 ± 4.4), but porewater NH4 concentration was often higher in dieback areas (overall average NH4 concentration was 138 ± 127 µM in dieback areas as compared to 33 ± 40 µM in healthy areas (particularly the 0 in NH4). These results suggest that the cause (or causes) of dieback was no longer present at the time of this study, and that transplants are a possibility for restoring affected areas.

Palomo, L., Meile, C. and Joye, S.B. 2013. Drought impacts on biogeochemistry and microbial processes in salt marsh sediments: a flow-through reactor approach. Biogeochemistry. 112(1-3):389-407. (DOI: 10.1007/s10533-012-9734-z)

Abstract
The effects of drought on salt marsh sediments from Sapelo Island, Georgia, were examined in flow-through reactor experiments. Three hydrological treatments were employed: a continuously flooded anoxic control, a periodic drought treatment that experienced alternate periods of flooding and drying, and a severe drought treatment, where sediment was exposed to drought (drying) for several weeks and then flooded; the effect of both buffered and non-buffered flooding solutions were examined. In permanently anoxic sediments as well as in sediments exposed to drought, organic carbon oxidation was dominated by SO4 2− reduction (SR) and SR rates increased over time. The shift from anoxic to oxic conditions in drought treatments significantly altered sediment geochemistry and pathways of microbial metabolism. Drought conditions favored suboxic mineralization processes, such as Fe(III) reduction and denitrification, which was fueled by NH4 + oxidation promoted by O2 delivered during drought conditions. Other major drought-induced changes included pH decrease, and altered concentrations of solid phase adsorbed metals.

Pendleton, L., Donato, D., Murray, B., Crooks, S., Jenkins, W., Sifleet, S., Craft, C., Fourequrean, J., Kaufman, J., Marba, N., Megonigal, P., Pidgeon, E., Bilbao-Bastida, V., Ullman, R., Herr, D., Gordon, D. and Baldera, A. 2012. Estimating global "blue carbon" emissions from conversion and degradation of coastal ecosystems. PLoS-ONE. 7:1-7.

Abstract
Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems—marshes, mangroves, and seagrasses—that may be lost with habitat destruction (‘conversion’). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this ‘blue carbon’ can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15–1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3–19% of those from deforestation globally, and result in economic damages of $US 6–42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of landuse conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the wellrecognized ecosystem services of coastal habitats.

Peng, D., Chen, L., Pennings, S.C. and Zhang, Y. 2018. Using a marsh organ to predict future plant communities in a Chinese estuary invaded by an exotic grass and mangrove. Limnology and Oceanography. 63:2595-2605. (DOI: 10.1002/lno.10962)

Abstract
Exotic species vary in how harmful they are. The earlier we can predict the outcome of an invasion, the moretime is available for management. We conducted a “marsh organ” experiment with six elevation treatments toevaluate how the exotic grass Spartina alterniflora, which has invaded almost the entire coastline of China,affects a native (Kandelia obovata) and an exotic (Sonneratia apetala) mangrove in Zhangjiang Estuary, southernChina. Survival of transplants in monoculture over two growing seasons in the marsh organ was high except atextreme high and low elevations. All three plants displayed hump-shaped patterns of biomass across elevationin monoculture, but K. obovata performed best at slightly higher and S. alterniflora at slightly lower elevations,whereas S. apetala performed well across all four intermediate elevations and grew larger than the other twoplants. In mixtures, S. alterniflora suppressed growth of mangrove seedlings of both species by up to 90%. Thecompetitive effect of S. alterniflora was greatest at intermediate elevations where its biomass was greatest. Whentransplanted into adjacent stands of S. alterniflora, K. obovata remained stunted, but S. apetala grew quickly andbegan to emerge from the canopy of S. alterniflora by the end of the second growing season. At this site, pastand ongoing disturbances to mature stands of K. obovata are likely to allow both exotics to increase inabundance. Aggressive management intervention will be needed to prevent estuaries in southern China fromtransitioning to near complete dominance by the exotic mangrove S. apetala.

Pennings, S.C. and Callaway, R.M. 2002. Parasitic plants: parallels and contrasts with herbivores. Oecologia. 131:479-489.

Abstract
Parasitic plants are common in natural communities, but are largely ignored in plant community theory. Interactions between parasitic plants and hosts often parallel those between herbivores and plants: both types of consumers display host preferences, reduce host biomass and alter host allocation patterns, modify plant community structure and dynamics, and mediate interactions between host plants and other organisms. In other cases, basic differences in mobility, hormonal and elemental composition and resource capture between plants and animals lead to different effects: parasitic plants have broad host ranges, affect and are affected by host plant physiology because of similar hormonal pathways between parasite and host, do not alter nutrient cycling as extensively as do herbivores, and may simultaneously parasitize and compete with hosts. Many fundamental aspects of the ecology of parasitic plants remain poorly studied, and research to date has been dominated by laboratory studies and studies of crop pests, rather than by studies of natural communities.

Pennings, S.C. and Silliman, B.R. 2005. Linking biogeography and community ecology: latitudinal variation in plant-herbivore interaction strength. Ecology. 86:2310-2319.

Abstract
Ecological interactions may vary geographically as a function of diversity, density, or per capita interaction strengths, but we know little about the relative importance of these three mechanisms. We examined variation in species richness, abundance, and interactions among leaf-chewing herbivores and the dominant salt-marsh plant Spartina alterniflora along the Atlantic Coast of the United States. High-latitude S. alterniflora plants are more palatable to herbivores than are low-latitude plants. Within this range of latitude, diversity and density of the dominant leaf-chewing consumers, snails and grasshoppers, in Spartina-dominated portions of the marsh varied little. Low-latitude plants, however, experienced much greater levels of leaf damage from consumers than did high-latitude plants. Per capita feeding rates of low-latitude snails (Littoraria irrorata) and grasshoppers (Orchelimum fidicinum) in the laboratory were greater than feeding rates of high-latitude snails (Melampus bidentatus) and grasshoppers (Conocephalus spartinae). In field experiments, low-latitude snails strongly suppressed S. alterniflora growth, but high-latitude snails had no effect on primary production. Thus, latitudinal differences in the effect of herbivores on plants (i.e., interaction strength), driven by differences in per capita effects among species, rather than differences in diversity or density, may contribute to selection for latitudinal differences in plant palatability. Because geographical differences in interaction strength can occur in the absence of differences in diversity or density, linking biogeography with community ecology will require experimental studies that explicitly measure interaction strength at multiple geographic locations.

Pennings, S.C. and Simpson, J.C. 2008. Like herbivores, parasitic plants are limited by host nitrogen content. Plant Ecology. 196:245-250. (DOI: 10.1007/s11258-007-9348-z)

Abstract
Herbivores generally benefit from increased plant nitrogen content, because the nitrogen content of animals is much higher than that of plants. Consequently, high plant nitrogen alleviates the profound stoichiometric imbalance that herbivores face in their diets. Parasitic plants provide the opportunity to test this generalization for consumers across kingdoms. We fertilized two microhabitats in a California salt marsh that were dominated by Salicornia virginica or a mixture of S. virginica and Jaumea carnosa. The nitrogen content of both host plants and of the holoparasite Cuscuta salina (dodder) increased in fertilized plots in both microhabitats. Cuscuta preferred to attack Jaumea, although Jaumea had lower nitrogen content than Salicornia. When host nitrogen content was altered by fertilizing plots, however, the percent cover of the parasite doubled. Although parasitic plants and their hosts have similar tissue nitrogen contents, suggesting no stoichiometric imbalance between host and consumer, parasitic plants do not feed on host tissue, but on host xylem and phloem, which are very low in nitrogen. Consequently, parasitic plants face the same dietary stoichiometric constraints as do herbivores, and both herbivores and holoparasitic plants may respond positively to increases in host nitrogen status.

Pennings, S.C., Clark, C.M., Cleland, E.E., Collins, S.L., Gough, L., Gross, K.L., Milchunas, D.G. and Suding, K.N. 2005. Do individual plant species show predictable responses to nitrogen addition across multiple experiments? OIKOS. 110:547-555.

Abstract
A number of experiments have addressed how increases in nitrogen availability increase the productivity and decrease the diversity of plant communities. We lack, however, a rigorous mechanistic understanding of how changes in abundance of particular species combine to produce changes in community productivity and diversity. Single experiments cannot provide insight into this issue because each species occurs only once per experiment, and each experiment is conducted in only one location; thus, it is impossible from single experiments to determine whether responses of particular species are consistent across environments or dependent on the particular environmental context in which the experiment was conducted. To address this issue, we assembled a dataset of 20 herbaceous species that were each represented in at least 6 different fertilization experiments and tested whether responses were general across experiments. Of the 20 species, one consistently increased in relative abundance and five consistently decreased across replicate experiments. A partially-overlapping group of 8 species displayed responses to nitrogen that varied predictably among experiments as a function of geographic location, neighboring species, or a handful of other community characteristics (ANPP, precipitation, species richness, relative abundance of focal species in control plots, and community composition). Thus, despite modest replication and a limited number of predictor variables, we were able to identify consistent patterns in response of 10 out of 20 species across multiple experiments. We conclude that the responses of individual species to nitrogen addition are often predictable, but that in most cases these responses are functions of the abiotic or biotic environment. Thus, a rigorous understanding of how plant species respond to nitrogen addition will have to consider not only the traits of individual plant species, but also aspects of the communities in which those plants live.

Pennings, S.C., Grant, M.-B. and Bertness, M.D. 2005. Plant zonation in low-latitude salt marshes: disentangling the roles of flooding, salinity and competition. Journal of Ecology. 93:159-167.

Abstract
We investigated the factors producing zonation patterns of the dominant plants in south-eastern USA salt marshes where Juncus roemerianus dominates the high marsh, and Spartina alterniflora the middle and low marsh. Juncus did not occur naturally in the Spartina zone and performed poorly when transplanted there, irrespective of whether neighbours were present or removed, indicating that its lower limit was set by physical stress. In contrast, although Spartina occurred naturally at low densities in the Juncus zone, it performed well if transplanted there only if neighbours were removed, indicating that its upper limit was set by competition. Parallel laboratory and field manipulations of flooding, salinity and competition indicated that the lower limit of Juncus was mediated by both flooding and salinity, but not by competition. The general mechanisms producing zonation patterns of vegetation in coastal salt marshes may be universal, as suggested by previous studies, but the importance of particular factors is likely to vary geographically. In particular, salinity stress probably plays a much more important role in mediating plant zonation patterns at lower latitudes. Our results suggest that the nature of ecological interactions is likely to vary geographically because of variation in the physical environment, and this variation must be taken into account in order to successfully generalize the results of field studies across geographical scales.

Pennings, S.C., Ho, C.-K., Salgado, C.S., Wieski, K., Davé, N.B., Kunza Vargas, A.E. and Wason, E.L. 2009. Latitudinal variation in herbivore pressure in Atlantic Coast salt marshes. Ecology. 90(1):183-195. (DOI: 10.1890/08-0222.1)

Abstract
Despite long-standing interest in latitudinal variation in ecological patterns and processes, there is to date weak and conflicting evidence that herbivore pressure varies with latitude. We used three approaches to examine latitudinal variation in herbivore pressure in Atlantic Coast salt marshes, focusing on five abundant plant taxa: the grass Spartina alterniflora, the congeneric rushes Juncus gerardii and J. roemerianus, the forb Solidago sempervirens, and the shrubs Iva frutescens and Baccharis halimifolia. Herbivore counts indicated that chewing and gall-making herbivores were typically ≥10 times more abundant at low-latitude sites than at high-latitude sites, but sucking herbivores did not show a clear pattern. For two herbivore taxa (snails and tettigoniid grasshoppers), correctly interpreting latitudinal patterns required an understanding of the feeding ecology of the species, because the species common at high latitudes did not feed heavily on plant leaves whereas the related species common at low latitudes did. Damage to plants from chewing herbivores was 2-10 times greater at low-latitude sites than at high-latitude sites. Damage to transplanted "phytometer" plants was 100 times greater for plants transplanted to low- than to high-latitude sites, and two to three times greater for plants originating from high- vs. low-latitude sites. Taken together, these results provide compelling evidence that pressure from chewing and gall-making herbivores is greater at low vs. high latitudes in Atlantic Coast salt marshes. Sucking herbivores do not show this pattern and deserve greater study. Selective pressure due to greater herbivore damage at low latitudes is likely to partially explain documented patterns of low plant palatability to chewing herbivores and greater plant defenses at low latitudes, but other factors may also play a role in mediating these geographic patterns.

Pennings, S.C., McCall, B.D. and Hooper-Bui, L. 2014. Effects of oil spills on terrestrial arthropods in coastal wetlands. Bioscience. 64:789-795. (DOI: 10.1093/biosci/biu118)

Abstract
Coastal wetlands are important to human well-being and vulnerable to oil spills. Research on biotic effects of oil has been focused on microbes,plants, and benthic invertebrates, neglecting terrestrial arthropods. We review how oil affects terrestrial arthropods in coastal marshes andsuggest future research topics. Terrestrial arthropods play important ecological roles in coastal marshes, affecting primary production anddecomposition and providing food to terrestrial and marine vertebrates. Some species are pests and disease vectors for humans and livestock.Terrestrial arthropods are sensitive to oil exposure and are suppressed even in lightly oiled sites where plants are not affected. Some arthropodslater reinhabit oiled marshes, which demonstrates that portions of the arthropod community may be resilient to oil exposure. However, oil thatremains in sediments may affect terrestrial populations for years after the spill. The sensitivity of arthropods to oil exposure makes them usefulindicators of marsh health following environmental impacts.

Pennings, S.C., Selig, E.R., Houser, L.T. and Bertness, M.D. 2003. Geographic variation in positive and negative interactions among salt marsh plants. Ecology. 84:1527-1538.

Abstract
A pressing problem for ecologists is determining whether our understanding of communities, often developed from work at fine scales, can explain processes across broader scales. Here, we explore whether models of positive interactions developed in southern New England can be applied to geographic scales. Salt marsh plants may interact positively by ameliorating harsh physical conditions such as salinity stress. Because marsh porewater salinities are higher in low- vs. high-latitude marshes, we tested the hypothesis that positive interactions are increasingly important at low latitudes. Previous work supported this hypothesis at the regional scale: within New England, positive interactions were rare in Maine but common in Rhode Island. We conducted parallel experiments in Georgia and Alabama to determine whether similar results would be obtained in a geographic comparison. Nine species of salt marsh plants were transplanted into control plots or plots with neighboring vegetation removed, in three marsh zones, at two sites each in Georgia and Alabama. Removing neighbors increased porewater salinities; nevertheless, plants usually performed best in neighbor-removal treatments, indicating that most interactions were competitive rather than facilitative. Several mechanisms might explain these results. For widely distributed species, southern individuals may be more salt tolerant than northern conspecifics. We tested this hypothesis by comparing the salt tolerance of northern and southern conspecifics of three species in a common garden experiment. In two species, southern plants were more salt tolerant than northern conspecifics. Although this pattern may explain the rarity of facilitation in the south for some species, it cannot explain our overall results because few species were studied in both geographic regions. The most likely explanation for our results is that northern marsh floras are dominated by salt-sensitive species that are likely to be facilitated by neighbors, whereas southern marsh floras are dominated by salt-tolerant species that are unlikely to benefit substantially from neighbor amelioration of soil salinities. These results illustrate the difficulties inherent in extrapolating results from even well understood systems to different geographic locations or scales. Intraspecific adaptations and community composition are often likely to vary geographically, complicating our efforts to construct geographically robust generalities about community structure and processes.

Pennings, S.C., Stanton, L.E. and Brewer, J.S. 2002. Nutrient effects on the composition of salt marsh plant communities along the southern Atlantic and Gulf Coasts of the United States. Estuaries. 25:1164-1173.

Abstract
Nutrient availability is known to mediate plant community structure in many systems, but relatively few studies of nutrient effects have been done in systems where strong gradients in physical stress might constrain the effects of nutrients. Recent studies in New England, United States, salt marshes indicate that nutrients may strongly mediate plant community composition by increasing the competitive ability of stress-tolerant species that are normally displaced by competition to recently-disturbed or low-intertidal habitats. It is unknown whether these results can be generalized to salt marshes in other geographic regions that experience different climates, tidal regimes, and edaphic conditions. To address the generality of these results from New England, we fertilized seven different mixtures of salt marsh plants at study sites on the southeast and Gulf coasts of the U.S. Two of these mixtures were studied in both geographic regions. Consistent with results from New England, fertilization always increased the biomass of the low-marsh dominant Spartina alterniflora and usually led to it increasing in dominance at the expense of high-marsh species. Fertilization also led to increased community dominance by Distichlis, but only in a mixture where it was already common. Fertilization led to changes in plant dominance patterns in four of the seven types of mixtures that we studied. Results were not a function of edaphic conditions, at least within the range included in our study, and were consistent between the southeastern and Gulf coasts, which experience markedly different tidal regimes. The broad similarity of these results suggests that changes in nutrient input may lead to predictable changes in the composition of similar salt marsh plant communities across large geographic areas despite site to site variation in the abiotic environment.

Pennings, S.C., Zimmer, M., Dias, N., Sprung, M., Davé, N., Ho, C.-K., Kunza, A., McFarlin, C., Mews, M., Pfauder, A. and Salgado, C. 2007. Latitudinal variation in plant-herbivore interactions in European salt marshes. Oikos. 116:543-549.

Abstract
Ecological interactions often vary geographically. Work in salt marshes on the Atlantic Coast of the United States has documented community-wide latitudinal gradients in plant palatability and plant traits that may be driven in part by greater herbivore pressure at low latitudes. To determine if similar patterns exist elsewhere, we studied six taxa of saltmarsh plants ( Atriplex, Juncus, Limonium, Salicornia, Spartina and Suaeda) at European sites at high (Germany and the Netherlands) and low (Portugal and Spain) latitudes. We conducted feeding assays using both native and non-native consumers, and documented patterns of herbivore damage in the field. As in the United States, high-latitude plants tended to be more palatable than low-latitude plants when offered to consumers in paired feeding assays in the laboratory, although assays with grasshopper consumers were less consistent than those with crab consumers, and plants in the field at low-latitude sites tended to experience greater levels of herbivore pressure than plants at high-latitude sites. Similarly, high-latitude leaf litter was more palatable than litter from low-latitude plants when offered to consumers in paired feeding assays in the laboratory. Latitudinal gradients in plant palatability and herbivore pressure may be a general phenomenon, and may contribute to latitudinal gradients in decomposition processes.

Peterson, R.N., Breier, J.C., Harmon, L.R., Brusa, J. and Hutchins, P.R. 2013. Development of a sparging chamber for field radon analysis. Journal of Radioanalytical and Nuclear Chemistry. 298:1347-1357. (DOI: 10.1007/s10967-013-2589-5)

Abstract
Radon-222 has become a widely used tracer of submarine groundwater discharge. However, remote field studies are often limited by the need to pump water to a spray chamber which degasses dissolved radon for subsequent analysis in the gaseous phase. We develop here a new method of degassing dissolved 222Rn, utilizing a stream of bubbles driven by the internal air pump of a commercial radon analyzer to achieve air:water partitioning equilibrium, eliminating the need to pump water. This system utilizes a sparging chamber, comprised of a slotted vertically-oriented pipe with bubbles produced in the bottom. A non-slotted section of the pipe at the top of the chamber forms a sealed headspace, allowing air to be circulated in a closed loop between the sparging chamber and a radon-in-air monitor. We found that such a sparging chamber needs to allow bubbles to rise through at least 45 cm of water column to function at equal efficiency as the standard protocol of the spray chamber. Under our optimized configuration, the sparging chamber operates as efficiently as the standard protocol at measuring dissolved 222Rn activities when encountering increasing 222Rn activities, and offers even greater gas exchange efficiency when dissolved 222Rn activities decrease. The sparging chamber offers a more field-friendly alternative to measuring 222Rn activities, as it eliminates the need to maintain a submersible pump throughout the measurement and it offers increased temporal resolution when variable 222Rn activities are expected.

Peterson, R.N., Meile, C., Peterson, L., Carter, M. and Miklesh, D.M. 2019. Groundwater discharge dynamics into a salt marsh tidal river. Estuarine, Coastal and Shelf Science.

Abstract
Exchange of groundwater is an important transfer mechanism for nutrients and pollutants between coastal aquifers and surface waters. Constraining such exchange in salt marshes - where biological productivity and biogeochemical cycling rates are among the highest of all coastal ecosystems – is vital for understanding ecosystem function and vulnerability. Here, we quantify groundwater discharge into the tidal Duplin River from the adjoining salt marsh near Sapelo Island, Georgia using high spatial and temporal resolution field measurements of radon-222. Field campaigns occurred for several weeks each summer during 2013, 2015, and 2016. Spatial surveys reveal a general increase in radon activity upstream through the Duplin River, which may result from either higher groundwater discharge or lower mixing rates in the headwaters. To distinguish between these possibilities, we use a radon mass balance model to determine groundwater input. We find that groundwater discharge (normalized to inundated marsh surface area) to the headwaters average 5.1 – 5.8 cm3/cm2 marsh/day across all three field campaigns, which are comparable to those to the main channel (averaging 6.0 – 6.5 cm3/cm2 marsh/day across all three field campaigns). Our work reveals a positive relationship between aerial extent of marsh inundation and groundwater discharge into the Duplin River. Discharge is generally maximal during falling tide, reflecting a hydraulic gradient driver, but also is significant prior to high tide, indicative of sediment compression as a driver of groundwater inputs. Constraining the relationship between marsh inundation and resulting groundwater dynamics is an integral aspect to assessing how salt marsh circulation processes may respond to intensifying inundation (from reduced sediment supply, subsidence, and/or rising sea levels).

Pimiento, C., Monaco, E., Barbour, A. and Silliman, B.R. 2013. Predation on speared lionfish /Pterois volitans/ by spotted moray /Gymnothorax moringa. Florida Scientist. 76(3-4):391-394.

Abstract
Little is known about predation on the red lionfish, Pterois volitans, in invaded habitats. In this note, we report for the first time a spotted moray, Gymnothorax moringa, successfully attacking and eating a still alive, but injured (speared) adult red lionfish in San Salvador, Bahamas. We describe the consumption of the red lionfish and the response behavior of the predator. Understanding predation pressures on red lionfish in the western Atlantic Ocean is of great significance given the rapid growth of this invasive species and its potential effects on populations of coral reef fish. This important problem is exacerbated by the fact that top predators have largely been overfished in the western Atlantic, thus removing potential predators for this invasive species. Our observation suggests that the spotted moray and, by extrapolation, other morays might represent a naturally occurring top-down control agent of invasive red lionfish. Muraenids in general eould play a critical role as bio-control forces because moray eel populations have been largely spared the effects of over fishing.

Platt, S.G., Elsey, R.M., Liu, H., Rainwater, T.R., Nifong, J.C., Rosenblatt, A.E., Heithaus, M. and Mazzotti, F.J. 2013. Frugivory and seed dispersal by crocodilians: an overlooked form of saurochory? Journal of Zoology. (DOI: 10.1111/jzo.12052)

Abstract
Saurochory (seed dispersal by reptiles) among crocodilians has largely beenignored, probably because these reptiles are generally assumed to be obligatecarnivores incapable of digesting vegetable proteins and polysaccharides. Hereinwe review the literature on crocodilian diet, foraging ecology, digestive physiologyand movement patterns, and provide additional empirical data from recent dietarystudies of Alligator mississippiensis. We found evidence of frugivory in 13 of 18(72.2%) species for which dietary information was available, indicating this behavioris widespread among the Crocodylia. Thirty-four families and 46 genera ofplants were consumed by crocodilians. Fruit types consumed by crocodiliansvaried widely; over half (52.1%) were fleshy fruits. Some fruits are consumed asgastroliths or ingested incidental to prey capture; however, there is little doubt thaton occasion, fruit is deliberately consumed, often in large quantities. Sensory cuesinvolved in crocodilian frugivory are poorly understood, although airborne andwaterborne cues as well as surface disturbances seem important. Crocodilianslikely accrue nutritional benefits from frugivory and there are no a priori reasonsto assume otherwise. Ingested seeds are regurgitated, retained in the stomach forindefinite and often lengthy periods, or passed through the digestive tract andexcreted in feces. Chemical and mechanical scarification of seeds probably occursin the stomach, but what effects these processes have on seed viability remainunknown. Because crocodilians have large territories and undertake lengthymovements, seeds are likely transported well beyond the parent plant before beingvoided. Little is known about the ultimate fate of seeds ingested by crocodilians;however, deposition sites could prove suitable for seed germination. Althoughthere is no evidence for a crocodilian-specific dispersal syndrome similar to thatdescribed for other reptiles, our review strongly suggests that crocodilians functionas effective agents of seed dispersal. Crocodilian saurochory offers a fertileground for future research.

Pontius, R.G., Krithivasan, r., Sauls, L., Yan, Y. and Zhang, Y. 2017. Methods to summarize change among land categories across time intervals. Journal of Land Use Science. 12(4):218-230. (DOI: 10.1080/1747423X.2017.1338768)

Abstract
Time-series maps have become more detailed in terms of numbers of categories and time points. Our paper proposes methods for raster datasets where detailed analysis of all categorical transitions would be initially overwhelming. We create two measurements: Incidents and States. The former is the number of times a pixel’s category changes across time intervals; the latter is the number of categories that a pixel represents across time points. The combinations of Incidents and States summarize change trajectories. We also describe categorical transitions in terms of annual flow matrices, which quantify the additional information generated by intermediate time points within the temporal extent. Our approach summarizes change at the pixel and landscape levels in ways that communicate where and how categories transition over time. These methods are useful to detect hotspots of change and to consider whether the apparent changes are real or due to map error.

Poretsky, R.S., Bano, N., Buchan, A., LeCleir, G., Kleikemper, J., Pickering, M., Pate, W.M., Moran, M.A. and Hollibaugh, J.T. 2005. Analysis of microbial gene transcripts in environmental samples. Applied and Environmental Microbiology. 71: 4121-4126.

Abstract
We analyzed gene expression in marine and freshwater bacterioplankton communities by the direct retrieval and analysis of microbial transcripts. Environmental mRNA, obtained from total RNA by subtractive hybridization of rRNA, was reverse transcribed, amplified with random primers, and cloned. Approximately 400 clones were analyzed, of which ?80% were unambiguously mRNA derived. mRNAs appeared to be from diverse taxonomic groups, including both Bacteria (mainly alpha- and gamma-Proteobactria) and Archaea (mainly Euryarchaeota). Many transcripts could be linked to environmentally important processes such as sulfur oxidation (soxA), assimilation of C1 compounds (fdh1B), and acquisition of nitrogen via polyamine degradation (aphA). Environmental transcriptomics is a means of exploring functional gene expression within natural microbial communities without bias toward known sequences, and provides a new approach for obtaining community- specific variants of key functional genes.

Poretsky, R.S., Sun, S., Mou, X. and Moran, M.A. 2010. Transporter genes expressed by coastal bacterioplankton in response to dissolved organic carbon. Environmental Microbiology. 12(3):616-627. (DOI: 10.1111/j.1462-2920.2009.02102.x)

Abstract
Coastal ocean bacterioplankton control the flow of dissolved organic carbon (DOC) from terrestrial and oceanic sources into the marine food web, and regulate the release of inorganic carbon to atmospheric and offshore reservoirs. While the fate of the chemically complex coastal DOC reservoir has long been recognized as a critical feature of the global carbon budget, it has been problematic to identify both the compounds that serve as major conduits for carbon flux and the roles of individual bacterioplankton taxa in mediating that flux. Here we analyse random libraries of expressed genes from a coastal bacterial community to identify sequences representing DOC-transporting proteins. Predicted substrates of expressed transporter genes indicated that carboxylic acids, compatible solutes, polyamines and lipids may be key components of the biologically labile DOC pool in coastal waters, in addition to canonical bacterial substrates such as amino acids, oligopeptides and carbohydrates. Half of the expressed DOC transporter sequences in this coastal ocean appeared to originate from just eight taxa: Roseobacter, SAR11, Flavobacteriales and five orders of γ-Proteobacteria. While all major taxa expressed transporter genes for some DOC components (e.g. amino acids), there were indications of specialization within the bacterioplankton community for others (e.g. carbohydrates, carboxylic acids and polyamines). Experimental manipulations of the natural DOC pool that increased the concentration of phytoplankton- or vascular plant-derived compounds invoked a readily measured response in bacterial transporter gene expression. This highly resolved view of the potential for carbon flux into heterotrophic bacterioplankton cells identifies possible bioreactive components of the coastal DOC pool and highlights differing ecological roles in carbon turnover for the resident bacterial taxa.

Porubsky, W.P., Joye, S.B., Moore, W.S., Tuncay, K. and Meile, C. 2011. Field measurements and modeling of groundwater flow and biogeochemistry at Moses Hammock, a backbarrier island on the Georgia coast. Biogeochemistry. 104:69-90. (DOI: 10.1007/s10533-010-9484-8)

Abstract
A combination of field measurements, laboratory experiments and model simulations were used to characterize the groundwater biogeochemical dynamics along a shallow monitoring well transect on a coastal hammock. A switch in the redox status of the dissolved inorganic nitrogen (DIN) pool in the well at the upland/saltmarsh interface occurred over the spring-neap tidal transition: the DIN pool was dominated by nitrate during spring tide and by ammonium during neap tide. A density-dependent reaction-transport model was used to investigate the relative importance of individual processes to the observed N redox-switch. The observed N redox-switch was evaluated with regard to the roles of nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), ammonium adsorption, and variations in inflowing water geochemistry between spring and neap tides.Transport was driven by measured pressure heads and process parameterizations were derived from field observations, targeted laboratory experiments, and the literature. Modeling results suggest that the variation in inflow water chemistry was the dominant driver of DIN dynamics and highlight the importance of spring-neap tide variations in the high marsh, which influences groundwater biogeochemistry at the marsh-upland transition.

Porubsky, W.P., Velasquez, L.E. and Joye, S.B. 2008. Nutrient replete benthic microalgae as a source of labile dissolved organic carbon to coastal waters. Estuaries and Coasts. 31(5):860-876. (DOI: 10.1007/s12237-008-9077-0)

Abstract
Dissolved organic carbon (DOC) flux dynamics were examined in the context of other biogeochemical cycles in intertidal sediments inhabited by benthic microalgae. In August 2003, gross oxygenic photosynthetic (GOP) rates, oxygen penetration depths, and benthic flux rates were quantified at seven sites along the Duplin River, GA, USA. Sediments contained abundant benthic microalgal (BMA) biomass with a maximum chlorophyll a concentration of 201 mg chl a m-2. Oxygen microelectrodes were used to determine GOP rates and O2 penetration depth, which were tightly correlated with light intensity. Baseline and 15N-nitrate amended benthic flux core incubations were employed to quantify benthic fluxes and to investigate the impact of BMA on sediment water exchange under nitrogen (N)-limited and N-replete conditions. Unamended sediments exhibited tight coupling between GOP and respiration and served as a sink for water column dissolved inorganic nitrogen (DIN) and a source of silicate and dissolved inorganic carbon (DIC). The BMA response to the N addition indicated sequential nutrient limitation, with N limitation followed by silicate limitation. In diel (light–dark) incubations, biological assimilation accounted for 83% to 150% of the nitrate uptake, while denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) accounted for <7%; in contrast, under dark conditions, DNF and DNRA accounted for >40% of the NO3 - uptake. The N addition shifted the metabolic status of the sediments from a balance of autotrophy and heterotrophy to net autotrophy under diel conditions, and the sediments served as a sink for water column DIN, silicate, and DIC but became a source of DOC, suggesting that the increased BMA production was decoupled from sediment bacterial consumption of DOC.

Porubsky, W.P., Weston, N.B. and Joye, S.B. 2009. Benthic metabolism and the fate of dissolved inorganic nitrogen in intertidal sediments. Estuarine Coastal and Shelf Science. 83(4):392-402. (DOI: 10.1016/j.ecss.2009.04.012)

Abstract
We determined patterns of benthic metabolism and examined the relative importance of denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) as sinks for nitrate (NO3−) in intertidal sediments in the presence and absence of benthic microalgal (BMA) activity. By influencing the activity of BMA, light regulated the metabolic status of the sediments, and, in turn, exerted strong control on sediment nitrogen dynamics and the fate of inorganic nitrogen. A pulsed addition of 15N-labeled NO3− tracked the effect and fate of dissolved inorganic nitrogen (DIN) in the system. Under illuminated conditions, BMA communities influenced benthic fluxes directly, via DIN uptake, and indirectly, by altering the oxygen penetration depth. Under dark hypoxic and anoxic conditions, the fate of water column NO3− was determined largely by three competing dissimilatory reductive processes; DNF, DNRA, and, on one occasion, anaerobic ammonium oxidation (anammox). Mass balance of the added 15N tracer illustrated that DNF accounted for a maximum of 48.2% of the 15NO3− reduced while DNRA (a minimum of 11.4%) and anammox (a minimum of 2.2%) accounted for much less. A slurry experiment was employed to further examine the partitioning between DNF and DNRA. High sulfide concentrations negatively impacted rates of both processes, while high DOC:NO3− ratios favored DNRA over DNF.

Reader, H.E. and Miller, W. 2014. Application of hyperspectral remote sensing reflectance data to photochemical rate calculations in the Duplin River, a tidal river on the coast of Georgia, USA. GIScience & Remote Sensing. 51(2):199-211. (DOI: 10.1080/15481603.2014.895583)

Abstract
Estuaries are photochemically dynamic environments with high carbon loads andrelatively small areas. The small area poses problems for large-scale satellite-basedremote sensing calculations, where the resolution is too coarse to distinguish land fromwater. Airborne remote sensing instruments have the potential to reveal the dynamicsof these areas with fine-scale resolution. In June 2006, hyperspectral remote sensingimagery, using an AISA Eagle instrument, was collected over the tidal Duplin River,Georgia, USA. A dark-water updated version of the SeaUV algorithm was applied tothe AISA remote sensing image to determine diffuse attenuation constants in theultraviolet and calculate surface photochemical production rates of two inorganicproducts – carbon monoxide (CO) and carbon dioxide (CO2). For an average day inJune at the study site, the modeled photoproduction rates for CO2 and CO averaged~7 × 10−1 nmol C/day/cm3 and ~3.5 × 10−2 nmol C/day/cm3, respectively.

Reimer, J.J., Cai, W.-J., Xue, L., Vargas, R., Noakes, S., Hu, X., Signorini, S.R., Mathis, J.T., Feely, R.A., Sutton, A.J., Sabine, C., Musielewicz, S., Chen, B. and Wanninkhof, R. 2017. Time series pCO2 at a coastal mooring: Internal consistency, seasonal cycles, and interannual variability. Continental Shelf Research. 145:95-108. (DOI: 10.1016/j.csr.2017.06.022)

Abstract
Marine carbonate system monitoring programs often consist of multiple observational methods that include underway cruise data, moored autonomous time series, and discrete water bottle samples. Monitored parameters include all, or some of the following: partial pressure of CO2 of the water (pCO2w) and air, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH. Any combination of at least two of the aforementioned parameters can be used to calculate the others. In this study at the Gray's Reef (GR) mooring in the South Atlantic Bight (SAB) we: examine the internal consistency of pCO2w from underway cruise, moored autonomous time series, and calculated from bottle samples (DIC-TA pairing); describe the seasonal to interannual pCO2w time series variability and air-sea flux (FCO2), as well as describe the potential sources of pCO2w variability; and determine the source/sink for atmospheric pCO2. Over the ~8.5 years of GR mooring time series, mooring-underway and mooring-bottle calculated-pCO2w strongly correlate with r-values > 0.90. pCO2w and FCO2 time series follow seasonal thermal patterns; however, seasonal non-thermal processes, such as terrestrial export, net biological production, and air-sea exchange also influence variability. The linear slope of time series pCO2w increases by 5.2 ± 1.4 µatm y−1 with FCO2 increasing 51–70 mmol m−2 y−1. The net FCO2 sign can switch interannually with the magnitude varying greatly. Non-thermal pCO2w is also increasing over the time series, likely indicating that terrestrial export and net biological processes drive the long term pCO2w increase.

Richards, C.L., Hamrick, J.L., Donovan, L.A. and Mauricio, R. 2004. Unexpectedly high clonal diversity of two salt marsh perennials across a severe environmental gradient. Ecology Letters. 2004(7):1155-1162.

Abstract
In salt marsh habitats, noted for their extreme environments, a widely held assumption is that a few large clones dominate plant populations. Using a large number of polymorphic allozyme loci, we were able to test this assumption for two salt marsh plants known to span extreme salinity gradients. For both species, clonal diversity was surprisingly high across populations: Simpson’s diversity indices were 0.96 and 0.99. Although clonal diversity was high, there was no pattern of association between specific clones or alleles with salt microhabitat. Our finding s suggest that sexual reproduction and recruitment from seeds may have been generally underappreciated as an important ecological force in the salt marsh. High clonal diversity has important implications for conservation and restoration of these critical coastal habitats. Furthermore, recent studies suggest that high levels of intraspecific diversity can affect a variety of community and ecosystem processes.

Richards, C.L., Pennings, S.C. and Donovan, L.A. 2005. Habitat range and phenotypic variation in salt marsh plants. Plant Ecology. 176:263-273.

Abstract
Ecologists have long speculated that species with wider environmental ranges would have broader ranges in phenotype; however, most tests of this hypothesis have involved small numbers of species and/or closely related taxa. We related phenotypic variation in twelve salt marsh plant species from six families to variation in four environmental variables using multiple regression. Within species, plant phenotype was predictably related to environmental variation. Salinity was the most common predictor of plant traits, followed by organic content, water content and elevation. Across species, regressions of single plant trait CVs on range (2 × SD) of single environmental variables were not significant and did not support the hypothesis that species occupying broad environmental ranges would have broad ranges in phenotypes. However, regression of a composite phenotypic PCA1 on a composite environmental PCA1 showed a marginally significant (P = 0.054). linear relationship for 10 species. Considering the different patterns of response across species, the lack of a relationship between variation in single phenotypic traits and single environmental variables is likely because the distantly-related taxa employed fundamentally different morphological and physiological strategies to respond to environmental stress gradients. The significant relationship between composite environmental and phenotypic variables reflects the complex nature of species phenotypic response to multivariate environmental gradients. Specifically, in this system, species increase variation in the number of leaves, but decrease variation in leaf size in response to an increase in range of salinity and decrease in range of water and organic content.

Richards, C.L., White, S.N., McGuire, M.A., Franks, S.J., Donovan, L.A. and Mauricio, R. 2010. Plasticity, not adaptation to salt level, explains variation along a salinity gradient in a salt marsh perennial. Special Issue: Genetic Structure and Adaptation in Coastal Ecosystems. Estuaries and Coasts. 33:840-852. (DOI: 10.1007/s12237-009-9186-4)

Abstract
Evolutionary ecologists have long been intrigued by the fact that many plant species can inhabit a broad range of environmental conditions, and that plants often exhibit dramatic differences in phenotype across environmental gradients. We investigated responses to salinity treatments in the salt marsh plant Borrichia frutescens to determine if the species is responding to variation in edaphic salt content through phenotypic plasticity or specialized trait response. We grew seedlings from fruits collected in high and low salt microhabitats, assigned seedlings to high and low salt treatments in a greenhouse and measured traits related to salt tolerance. All traits were highly plastic in response to salinity. Plants from the two microhabitats did not differ in trait means or respond differently to the treatments. These results suggest that environmental differences between the two microhabitats are not creating genotypes adapted to high and low salt levels. In addition, despite evidence for variation in allozyme markers in this population, there was no significant genotypic variation (family effect) in any of the trait means measured across microhabitats. There was variation in plasticity for only leaf Na and leaf B concentration. The high degree of plasticity for all traits and the lack of differences among microhabitats across the salinity gradient suggest plasticity may be fixed for this species.

Robinson, J.D., Diaz-Ferguson, E., Poelchau, M., Pennings, S.C., Bishop, T.D. and Wares, J.P. 2010. Multiscale Diversity in the Marshes of the Georgia Coastal Ecosystems LTER. Estuaries and Coasts. 33(4):865-877. (DOI: 10.1007/s12237-009-9188-2)

Abstract
Factors that maintain genetic and species diversity may act in concert in natural ecosystems. Here, we investigate correlations between genetic diversity (in eight salt marsh species) and community species diversity. A significant positive correlation existed between genetic diversity and species richness, although the relationship was not significant for any species individually. Nonetheless, four of the eight comparisons showed strong positive relationships between genetic and species diversity. Additionally, several abiotic variables were used in a model selection procedure to determine what site-level characteristics might drive differences in genetic diversity in this system. The rate of larval influx, as measured by barnacle abundance on Spartina alterniflora, was the strongest predictor of site-level genetic diversity in our samples. Our results suggest that estuarine management efforts should consider recruitment rates when selecting areas for protection.

Roebuck, J., Medeiros, P.M., Letourneau, M.L. and Jaffe, R. 2018. Hydrological controls on the seasonal variability of dissolved and particulate black carbon in the Altamaha River, GA. Journal of Geophysical Research - Biogeosciences. 123:3055-3071. (DOI: 10.1029/2018JG004406)

Abstract
Rivers play an important role in the transport of organic carbon from terrestrial to marine environments. A significant portion of this material is black carbon (BC), a residue of incomplete biomass and fossil fuel combustion. BC is mobilized in fluvial systems as both particulate BC (PBC) and dissolved BC (DBC) and the export of BC to coastal environments may have significant implications for carbon cycling in marine environments. However, while little is known regarding the potential connectivity between riverine export of PBC and DBC or the potential importance of such a relationship in constraining future BC budgets, current knowledge suggests that fluvial export of PBC and DBC are decoupled in small fire‐impacted watersheds. This study aims to further address this subject on a larger watershed scale. For this study, thirteen monthly samples were collected (Sept. 2015 ‐ Sept. 2016) near the mouth of the Altamaha River, Georgia. PBC and DBC were characterized using the benzenzepolycarboxylic acid method. Seasonal hydrology and regional shifts in storm events play an important role for both PBC and DBC export during high flow months. The DBC concentrations were comparable among wet and dry seasons, whereas evidence of seasonal salt‐water intrusions suggests an additional estuarine contribution of PBC at the sampling location. The DBC and PBC fluxes were generally coupled, although this pattern was disrupted during initial storm pulses. While this is the first report of potential coupling between DBC and PBC export, environmental drivers controlling this behavior between DBC and PBC remain to be constrained.

Rosenblatt, A.E., Heithaus, M., Mather, M., Matich, P., Nifong, J.C., Ripple, W. and Silliman, B.R. 2013. The Roles of Large Top Predators in Coastal Ecosystems: New Insights from Long Term Ecological Research. Special Issue: Coastal Long Term Ecological Research. Oceanography. 26(3):156 - 167. (DOI: http://dx.doi.org/10.5670/oceanog.2013.59)

Abstract
During recent human history, human activities such as overhunting and habitat destruction have severely impacted many large top predator populations around the world. Studies from a variety of ecosystems show that loss or diminishment of top predator populations can have serious consequences for population and community dynamics and ecosystem stability. However, there are relatively few studies of the roles of large top predators in coastal ecosystems, so that we do not yet completely understand what could happen to coastal areas if large top predators are extirpated or significantly reduced in number. This lack of knowledge is surprising given that coastal areas around the globe are highly valued and densely populated by humans, and thus coastal large top predator populations frequently come into conflict with coastal human populations. This paper reviews what is known about the ecological roles of large top predators in coastal systems and presents a synthesis of recent work from three coastal eastern US Long Term Ecological Research (LTER) sites where long-term studies reveal what appear to be common themes relating to the roles of large top predators in coastal systems. We discuss three specific themes: (1) large top predators acting as mobile links between disparate habitats, (2) large top predators potentially affecting nutrient and biogeochemical dynamics through localized behaviors, and (3) individual specialization of large top predator behaviors. We also discuss how research within the LTER network has led to enhanced understanding of the ecological roles of coastal large top predators. Highlighting this work is intended to encourage further investigation of the roles of large top predators across diverse coastal aquatic habitats and to better inform researchers and ecosystem managers about the importance of large top predators for coastal ecosystem health and stability.

Rosenblatt, A.E., Nifong, J.C., Heithaus, M., Mazzotti, F.J., Cherkiss, M., Jeffery, B., Elsey, R.M., Decker, R., Silliman, B.R., Guillette, L., Lowers, R. and Larson, J. 2015. Factors affecting individual foraging specialization and temporal diet stability across the range of a large “generalist” apex predator. Special Issue: INDIVIDUAL-LEVEL NICHE SPECIALIZATION. Oecologia. 178:5-16. (DOI: 10.1007/s00442-014-3201-6)

Abstract
Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and intraspecific competition on INS in small-bodied species for short time periods, with less attention paid to INS in large-bodied reptilian predators and the effects of available prey types on INS. We investigated the prevalence, causes, and consequences of INS in foraging behaviors across different populations of American alligators (Alligator mississippiensis), the dominant aquatic apex predator across the southeast US, using stomach contents and stable isotopes. Gut contents revealed that, over the short term, although alligator populations occupied wide ranges of the INS spectrum, general patterns were apparent. Alligator populations inhabiting lakes exhibited lower INS than coastal populations, likely driven by variation in habitat type and available prey types. Stable isotopes revealed that over longer time spans alligators exhibited remarkably consistent use of variable mixtures of carbon pools (e.g., marine and freshwater food webs). We conclude that INS in large-bodied reptilian predator populations is likely affected by variation in available prey types and habitat heterogeneity, and that INS should be incorporated into management strategies to efficiently meet intended goals. Also, ecological models, which typically do not consider behavioral variability, should include INS to increase model realismand applicability.

Runfola, D. and Pontius, R.G. 2013. Measuring the temporal instability of land change using the Flow matrix. International Journal of Geographical Information Science. 27(9):1696-1716. (DOI: 10.1080/13658816.2013.792344)

Abstract
This article introduces the Flow matrix, which expresses the sizes of transitions among categories between two time points. We use the Flow matrix to create a metric R that measures the instability of annual change among time intervals that partition the time extent. Specifically, R is the proportion of change that would need to be reallocated to different time interval(s) to achieve uniform change during the time extent. This article computes R for 10 Long Term Ecological Research (LTER) sites and for seven case studies from published land change data. Of the 10 LTER sites analyzed, the Andrews site in Oregon had the highest R value (37.1% of change), while the Luquillo site in Puerto Rico had the lowest (1.7% of change). We analyze the mathematical behavior of R, especially with respect to how the partitioning of the time extent into intervals can influence R.

Sala, N., Bertness, M.D. and Silliman, B.R. 2008. The Dynamics of Top-down and Bottom-up control in New England salt marshes. Oikos. 117(7):1050-1056. (DOI: 10.1111/j.0030-1299.2008.16296.x)

Abstract
Traditionally, salt marsh ecosystems were thought to be controlled exclusively by bottom–up processes. Recently, this paradigm has shifted to include top–down control as an additional primary factor regulating salt-marsh community structure. The most recent research on consumer impacts in southern US marshes has shown that top–down forces often interact with biotic and abiotic factors, such as secondary fungal infection in grazer-induced wounds, soil nutrients and climatic variation, to influence ecosystem structure. In a more northern salt marsh, located in New England, we examined the separate and interactive effects of nutrient availability, insect herbivory and secondary fungal infection, on growth of the foundation species, Spartina alterniflora. We used a factorial design with two levels of nutrients (control and addition) insects (control and removal) and fungi (control and removal). Nutrient addition increased plant biomass by 131% in the absence of herbivores. When insect consumers were allowed access to fertilized plots, biomass was reduced by nearly 45% when compared with treatments with nutrients and insecticide. In contrast, insect herbivores did not affect plant biomass in unfertilized control treatments. These differences suggest that consumer effects are triggered under high nutrient levels only. We also found that secondary fungal infections in grazer-induced wounds, in contrast to lower latitude marshes, did not significantly impact primary production. Our results suggest that while New England salt marshes may typically be under bottom–up control, eutrophication can trigger dual control with inclusion of top–down regulation. However, unlike lower latitude marshes, consumer control of plant growth in northern US salt marshes is not dependent on herbivores facilitating fungal infections that then control grass growth, suggesting that the intensity of disease mediated top–down control by small grazers may be regulated by climate and/or grazer identity that co-vary with latitude.

Salgado, C.S. and Pennings, S.C. 2005. Latitudinal variation in palatability of salt-marsh plants: are differences constitutive? Ecology. 86(6):1571-1579.

Abstract
Biogeographic theory argues that consumer–prey interactions are more intense, and prey defenses better developed, at lower latitudes. Along the Atlantic Coast of the United States, low-latitude salt marsh plants are less palatable than high-latitude conspecifics. To test the hypothesis that latitudinal variation in palatability would occur in the absence of geographically different environmental cues (i.e., that differences in palatability are constitutive rather than induced by climate or herbivore damage), we grew high- and low-latitude individuals of three species of salt marsh plants from seeds (Solidago sempervirens) or rhizome cuttings (Distichlis spicata and Spartina alterniflora) in a commongarden greenhouse environment, and compared their palatability to herbivores over time. We also quantified leaf toughness and nitrogen content over time in order to help explain results of feeding assays. High-latitude plants were always more palatable to herbivores than low-latitude conspecifics. Latitudinal variation in plant traits depended on the plant species. Toughness varied as a function of latitude for Spartina, with low-latitude plants being consistently tougher than high-latitude conspecifics. For all generations of Spartina, and for seed-propagated Solidago, high-latitude plants had a higher nitrogen content than low-latitude conspecifics. The fact that latitudinal differences in palatability and traits of salt marsh plants persisted in a common-garden environment suggests that this variation is constitutive, and likely under genetic control, rather than a plastic response to environmental cues. These results are consistent with the theory that latitudinal differences in herbivory have selected for geographical variation in plant palatability, although we cannot rule out other selective forces that may also vary across latitude.

Sanchez, C., Gaiser, E., Saunders, C., Wachnicka, A., Oehm, N. and Craft, C.B. 2013. Exploring siliceous subfossils as a tool for inferring past water level and hydroperiod in Everglades marshes. Journal of Paleolimnology. 45:49-66. (DOI: 10.1007/s10933-012-9624-3)

Abstract
Successfully rehabilitating drained wetlands through hydrologic restoration is dependent on defining restoration targets, a process that is informed by pre-drainage conditions, as well as understanding linkages between hydrology and ecosystem structure. Paleoecological records can inform restoration goals by revealing long-term patterns of change, but are dependent on preservation of biomarkers that provide meaningful interpretations of environmental change. In the Florida Everglades, paleohydrological hind-casting could improve restoration forecasting, but frequent drying of marsh soils leads to poor preservation of many biomarkers. To determine the effectiveness of employing siliceous subfossils in paleohydrological reconstructions, we examined diatoms, plant and sponge silico-sclerids from three soil cores in the central Everglades marshes. Subfossil quality varied among cores, but the abundance of recognizable specimens was sufficient to infer 1,000–3,000 years of hydrologic change at decadal to centennial resolution. Phytolith morphotypes were linked to key marsh plant species to indirectly measure fluctuations in water depth. A modern dataset was used to derive diatom-based inferences of water depth and hydroperiod (R2 = 0.63, 0.47; RMSE = 14 cm, 120 days, respectively). Changes in subfossil quality and abundances at centennial time-scales were associated with mid-Holocene climate events including the Little Ice Age and Medieval Warm Period, while decadal-scale fluctuations in assemblage structure during the twentieth century suggested co-regulation of hydrology by cyclical climate drivers (particularly the Atlantic Multidecadal Oscillation) and water management changes. The successful reconstructions based on siliceous subfossils shown here at a coarse temporal scale (i.e., decadal to centennial) advocate for their application in more highly resolved (i.e., subdecadal) records, which should improve the ability of water managers to target the quantity and variability of water flows appropriate for hydrologic restoration.

Schaefer, S.C. and Alber, M. 2007. Temperature controls a latitudinal gradient in the proportion of watershed nitrogen exported to coastal ecosystems. Biogeochemistry. 85(3):333-346. (DOI: 10.1007/s10533-007-9144-9)

Abstract
Increased export of biologically available nitrogen (N) to the coastal zone is strongly linked to eutrophication, which is a major problem in coastal marine ecosystems (NRC (2000) Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. National Academy Press, Washington, DC; Bricker et al. (1999) National Estuarine Eutrophication Assessment. Effects of nutrient enrichment in the nation’s estuaries. NOAA-NOS Special Projects Office, Silver Spring, MD). However, not all of the nitrogen input to a watershed is exported to the coast (Howarth et al. (1996) Biogeochemistry 35:75–139; Jordan and Weller (1996) Bioscience 46:655–664). Global estimates of nitrogen export to coasts have been taken to be 25% of watershed input, based largely on northeastern U.S. observations (Galloway et al. (2004) Biogeochemistry 70:153–226; Boyer et al. (2006) Global Biogeochem Cycle 20:Art. No. GB1S91). We applied the N budgeting methodology developed for the International SCOPE Nitrogen project (Howarth et al. (1996) Biogeochemistry 35:75–139; Boyer et al. (2002) Biogeochemistry 57:137–169) to 12 watersheds in the southeastern U.S., and compared them with estimates of N export for 16 watersheds in the northeastern U.S. (Boyer et al. (2002) Biogeochemistry 57:137–169). In southeastern watersheds, average N export was only 9% of input, suggesting the need for downward revision of global estimates. The difference between northern and southern watersheds is not a function of the absolute value of N inputs, which spanned a comparable range and were positively related to export in both cases. Rather, the proportion of N exported was significantly related to average watershed temperature (% N export = 58.41 e-0.11 * temperature; R 2 = 0.76), with lower proportionate nitrogen export in warmer watersheds. In addition, we identified a threshold in proportionate N export at 38°N latitude that corresponds to a reported breakpoint in the rate of denitrification at 10–12°C. We hypothesize that temperature, by regulating denitrification, results in increased proportionate N export at higher latitudes. Regardless of the mechanism, these observations suggest that temperature increases associated with future climate change may well reduce the amount of nitrogen that reaches estuaries, which will have implications for coastal eutrophication.

Schaefer, S.C. and Alber, M.A. 2007. Temporal and spatial trends in nitrogen and phosphorus inputs to the watershed of the Altamaha River, Georgia, USA. Biogeochemistry. 86(3):231-249. (DOI: 10.1007/s10533-007-9155-6)

Abstract
The watershed of the Altamaha River, Georgia, is one of the largest in the southeastern U.S., draining 36,718 km2 (including parts of metro Atlanta). We calculated both nitrogen (fertilizer, net food and feed import, atmospheric deposition, and biological N fixation in agricultural and forest lands) and phosphorus (fertilizer and net food and feed import) inputs to the watershed for 6 time points between 1954 and 2002. Total nitrogen inputs rose from 1,952 kg N km-2 yr-1 in 1954 to a peak of 3,593 kg N km-2 yr-1 in 1982 and then declined to 2,582 kg N km-2 yr-1 by 2002. Phosphorus inputs rose from 409 kg P km-2 yr-1 in 1954 to 532 kg P km-2 yr-1 in 1974 before declining to 412 kg P km-2 yr-1 in 2002. Fertilizer tended to be the most important input of both N and P to the watershed, although net food and feed import increased in importance over time and was the dominant source of N input by 2002. When considered on an individual basis, fertilizer input tended to be highest in the middle portions of the watershed (Little and Lower Ocmulgee and Lower Oconee sub-watersheds) whereas net food and feed imports were highest in the upper reaches (Upper Oconee and Upper Ocmulgee sub-watersheds). Although the overall trend in recent years has been towards decreases in both N and P inputs, these trends may be offset due to continuing increases in animal and human populations.

Schaefer, S.C. and Hollibaugh, J.T. 2017. Temperature Decouples Ammonium and Nitrite Oxidation in Coastal Waters. Environmental Science and Technology. 51(6):3157-3164. (DOI: 10.1021/acs.est.6b03483)

Abstract
Nitrification is a two-step process linking the reduced and oxidized sides of the nitrogen cycle. These steps are typically tightly coupled with the primary intermediate, nitrite, rarely accumulating in coastal environments. Nitrite concentrations can exceed 10 µM during summer in estuarine waters adjacent to Sapelo Island, Georgia, U.S.A. Similar peaks at other locations have been attributed to decoupling of the two steps of nitrification by hypoxia; however, the waters around Sapelo Island are aerobic and well-mixed. Experiments examining the response to temperature shifts of a nitrifying assemblage composed of the same organisms found in the field indicate that ammonia- and nitrite-oxidation become uncoupled between 20 and 30 °C, leading to nitrite accumulation. This suggests that nitrite peaks in coastal waters might be explained by differences in the responses of ammonia- and nitrite-oxidizers to increased summer temperatures. Analysis of field data from 270 stations in 29 temperate and subtropical estuaries and lagoons show transient accumulation of nitrite driven primarily by water temperatures, rather than by hypoxia. Increased climate variability and warming coastal waters may therefore increase the frequency of these nitrite peaks, with potential ecosystem consequences that include increased N2O production, NO2– toxicity, and shifts in phytoplankton community composition.

Schaefer, S.C., Hollibaugh, J.T. and Alber, M. 2009. Watershed nitrogen input and riverine export on the west coast of the U.S. Biogeochemistry. 93(3):219-233. (DOI: 10.1007/s10533-009-9299-7)

Abstract
This study evaluated the sources, sinks, and factors controlling net export of nitrogen from watersheds on the west coast of the US. We calculated input of new N to 22 watersheds for 1992 and 2002. 1992 inputs ranged from 541-11,644 kg N km-2 yr-1, with an overall area-weighted average of 1,870 kg N km-2 yr-1. In 2002, the range of inputs was 490-10,875 kg N km-2 yr-1, averaging 2,158 kg N km-2 yr-1. Fertilizer was the most important source of new N, averaging 956 (1992) and 1,073 kg N km-2 yr-1 (2002). Atmospheric deposition was the next-most important input, averaging 833 (1992) and 717 kg N km-2 yr-1 (2002), followed by biological N fixation in agricultural lands. Riverine N export, calculated based on measurements taken at the furthest downstream USGS water quality monitoring station, averaged 165 (1992) and 196 kg N km-2 yr-1 (2002), although data were available for only 7 watersheds at the latter time point. Downstream riverine N export was correlated with variations in streamflow (export=0.94*streamflow-5.65, R2=0.66), with N inputs explaining an additional 16% of the variance (export=1.06*streamflow+0.06*input–227.78, R2=0.82). The percentage of N input that is exported averaged 12%. Percent export was also related to streamflow (%export=0.05*streamflow-2.61, R2=0.60). The correlations with streamflow are likely a result of its large dynamic range in these systems. However, the processes that control watershed N export are not yet completely understood.

Schalles, J.F. and Hladik, C.M. 2012. Mapping phytoplankton chlorophyll in turbid, Case 2 estuarine and coastal waters. Special Issue: VIS-NIR Spectroscopy in Plant Sciences. Israel Journal of Plant Science. 60(1-2):169-192. (DOI: 10.1560/IJPS.60.1-2.169)

Abstract
We tested variants of semianalytic algorithms for estimating phytoplankton chlorophyll pigment in Case 2 waters. Since 2002 we sampled 279 stations in 22 estuaries, bays and near shore at seven National Estuarine Research Reserves between Delaware and Texas (USA). The following median values and ranges were observed: chlorophyll a = 17.4 µg/L3 (0.2 – 490.1); total suspended solids = 23.4 mg/L dry weight (0.7 – 191.1); and CDOM absorbance (440 nm) = 3.11 m-1 (0.00 – 21.08). Spectroradiometers measured volume reflectance at each station. Sampling was designed to capture upriver to coastal mixing gradients. Algorithms utilized features in the red and lower NIR, with interference adjustments for CDOM absorption and non-algal particle scatter using bands in either the green (550 nm) or NIR between 723-739 nm. Our best two algorithms were re-parameterized using matchups with AISA Eagle imagery. Examples of pigment classification using these adjusted models are presented for five studies: dinoflagellate bloom in Maryland, tidal watershed in Georgia, estuarine reserve and neighboring refinery in Mississippi, shallow ponds important to Whooping Cranes in Texas, and transect capturing transitions between the Nueces River and Corpus Christi Bay in Texas. These analyses were useful in addressing issues important to coastal management.

Schalles, J.F., Hladik, C.M., Lynes, A.R. and Pennings, S.C. 2013. Landscape estimates of habitat types, plant biomass, and invertebrate densities in a Georgia salt marsh. Special Issue: Coastal Long Term Ecological Research. Oceanography. 26:88-97. (DOI: 10.5670/oceanog.2013.50)

Abstract
Salt marshes often contain remarkable spatial heterogeneity at multiple scales across the landscape. A combination of advanced remote-sensing approaches (hyperspectral imagery and lidar) and conventional field survey methods was used to produce detailed quantifications and maps of marsh platform geomorphology, vegetation composition and biomass, and invertebrate patterns in a Georgia (USA) salt marsh. Community structure was largely related to hydrology, elevation, and soil properties. Both abiotic drivers and community patterns varied among subwatersheds and across the landscape at larger spatial scales. The authors conclude that measurements of marsh ecosystem structure and processes are spatially contextual and not scalable without detailed geospatial analysis. Efforts to protect and restore coastal marshes must strive to document, understand, and conserve this inherent spatial complexity.

Schmidt, J.P., Moore, R. and Alber, M. 2014. Integrating ecosystem services and local government finances intoland use planning: A case study from coastal Georgia. Landscape and Urban Planning. 122:56 - 67. (DOI: 10.1016/j.landurbplan.2013.11.008)

Abstract
This work presents a novel approach to assessing the impact of future growth in rural regions faced with rapid growth. We investigate one of the most rural counties on the eastern coast of the U.S. (McIntosh County, Georgia) from the dual perspective of (1) ecosystem services and (2) costs assumed by local government. As land cover in our focal locality is overwhelmingly forest or wetland, we compiled estimates from multiple sources to map the value per ha/year of (1) timber sales and recreational leases to private landowners and (2) a suite of non-market public amenities: rare species habitat, carbon sequestration, flood control, pollution treatment, water supply, and storm protection. We then quantified, based on county budgets, expenditures and revenues deriving from major land use categories (residential, commercial/industrial, agricultural/open-space). Results indicate that (1) forested wetlands generate relatively little revenue to either private landowners or in taxes to the county from extractive uses, but have very high value relative other land cover types in the provision of ecosystem services, (2) forest lands contribute much more in revenue than they receive in services, whereas residential properties cost more in services, than they generate in revenue, and (3) significant gains in both ecosystem service preservation, hazard reduction, and in lower costs to the county in municipal services could be achieved by restricting new development from within the Federal Insurance Rate Map (FIRM)-determined 500 year floodplain.

Schultz, G. and Ruppel, C. 2002. Constraints on hydraulic parameters and implications for groundwater flux across the upland-estuary interface. Journal of Hydrology. 260:255-269.

Abstract
Analyses of independent laboratory- and field-scale measurements from two sites on Sapelo Island, Georgia reveal heterogeneity in hydraulic parameters across the upland±estuary interface. Regardless of the method used (short-duration pumping tests, amplitude attenuation of tidal pumping data, sediment grain size distributions, and falling head permeameter tests), we obtain hydraulic conductivity of ~10^-4 m s^-1 for the fine-grained, well-sorted, clean sands that make up the upland areas. Proximal to the upland-estuary boundary, the tidal pumping analyses and permeameter tests suggest that hydraulic conductiv­ities decrease by more than two orders of magnitude, a result consistent with the presence of a clogging layer. Such a clogging layer may arise due to a variety of physical, chemical, or biological processes. The extent and orientation of the layers of reduced hydraulic conductivity near the upland-estuary boundary influence the nature of the aquifer's response to tidal forcing. Where the lower conductivity layer forms a relatively flat creek bank, tidal pumping produces a primarily mechanical response in the adjacent aquifer. Where the creek bank is nearly vertical, there is a more direct hydraulic connection between the tidal creek and the adjacent aquifer. The clogging layer likely contributes to the development of complicated flow pathways across the upland-estuary boundary. Effective flow paths calculated from tidal pumping data terminate within the marsh, beyond the boundary of the upland aquifer, suggesting a diffuse regime of groundwater discharge in the marsh. We postulate that, in many settings, submarsh flow may be as important as seepage faces for groundwater discharge into the marsh-estuary complex.

Schultz, G.M. and Ruppel, C.D. 2005. Inversion of inductive electromagnetic data in highly conductive terrains. Geophysics. 70:G16-G28.

Abstract
Despite the increasing use of controlled-source frequency-domain EM data to characterize shallow subsurface structures, relatively few inversion algorithms have been widely applied to data from real-world settings, particularly in high-conductivity terrains. In this study, we develop robust and convergent regularized, least-squares inversion algorithms based on both linear and nonlinear formulations of mutual dipole induction for the forward problem. A modified version of the discrepancy principle based on a priori information is implemented to select optimal smoothing parameters that simultaneously guarantee the stability and best-fit criteria. To investigate the problems of resolution and equivalence, we consider typical layered-earth models in one and two dimensions using both synthetic and observed data. Synthetic examples show that inversions based on the nonlinear forward model more accurately resolve subsurface structure, and that inversions based on the linear forward model tend to drastically underpredict high conductivities at depth. Inversions of actual field data from well-characterized sites (e.g., National Geotechnical Experimentation Site; sand-dominated coastal aquifer in the Georgia Bight) are used to test the applicability of the model to terrains with different characteristic conductivity structure. A comparison of our inversion results with existing conepenetrometer and downhole-conductivity data from these field sites demonstrates the ability of the inversions to constrain conductivity variations in practical applications.

Schutte, C., Hunter, K.S., McKay, P., Di Iorio, D., Joye, S.B. and Meile, C. 2013. Patterns and controls of nutrient concentrations in a southeastern United States tidal creek. Special Issue: Coastal Long Term Ecological Research. Oceanography. 26(3):12-139. (DOI: http://dx.doi.org/10.5670/oceanog.2013.55)

Abstract
Terrestrial inputs largely govern nutrient delivery to the coastal ocean, and subsequent processes transform these nutrients in the land-ocean transition zone. Here, we describe spatial and temporal patterns in surface water chemistry from the Duplin, a salt marsh/tidal creek system located in coastal Georgia, USA. Key drivers of nutrient concentration patterns in the Duplin include discharge from the nearby Altamaha River, groundwater inputs, exchange with the marsh platform, and biological processes within the tidal creek. Altamaha River discharge is correlated with salinity in the Duplin, but the processes taking place within the Duplin watershed regulate the distribution of other dissolved and particulate materials. Long-term data sets advance our understanding of the relative importance of these processes in generating the observed patterns in surface water chemistry. This knowledge improves our ability to predict how coastal systems will respond to anthropogenic perturbations.

Schutte, C., Joye, S.B., Wilson, A.M., Evans, T., Moore, W.S. and Casciotti, K. 2015. Intense nitrogen cycling in permeable intertidal sediment revealed by a nitrous oxide hotspot. Global Biogeochemical Cycles. 29(10):1584–1598. (DOI: 10.1002/2014GB005052)

Abstract
Approximately 40% of the total global rate of nitrogen fixation is the result of human activities, and most of this anthropogenic nitrogen is used to fertilize agricultural fields. Approximately 23% of the applied agricultural nitrogen is delivered to the coastal zone, often reducing water quality and driving eutrophication. Nitrogen cycling in coastal sediments can mitigate eutrophication by removing bioavailable nitrogen. However, some of these processes generate nitrous oxide, a potent greenhouse gas, as a by-product. Here we report the discovery of a nitrous oxide production hot spot in shallow barrier island sands. Nitrous oxide concentrations, production and consumption rates, vertical diffusion fluxes, and flux to the atmosphere were measured across triplicate depth profiles. Using a mass balance approach, rates of net nitrous oxide production were estimated to be 40 µmol m−2 d−1. This production was driven by a hot spot of nitrate consumption that removed bioavailable nitrogen from the coastal environment at a rate of 10 mmol m−2 d−1, a rate that is comparable with the highest rates of denitrification reported for coastal sediments.

Schutte, C., Wilson, A.M., Evans, T., Moore, W.S. and Joye, S.B. 2016. Methanotrophy controls groundwater methane export from a barrier island. Geochimica et Cosmochimica Acta. 179:242-256. (DOI: 10.1016/j.gca.2016.01.022)

Abstract
Methane concentrations can be high in coastal groundwater, resulting in methane export driven by submarine groundwater discharge. However, the magnitude of this methane flux depends significantly on the rate of methanotrophy, the often overlooked process of microbial methane consumption that occurs within coastal aquifer sediments. Here we describe a zone of methanogenesis within the freshwater lens of a barrier island aquifer and investigate the methane source/sink behavior of the barrier island system as a whole. The median concentration of methane dissolved in fresh groundwater beneath the center of the island was 0.6 mM, supported by high rates of potential methanogenesis (22 mmol m−2 day−1). However, rates of microbial methane consumption were also elevated in surrounding sediments (18 mmol m−2 day−1). Groundwater flowing from the zone of methanogenesis to the point of discharge into the ocean had a long residence time within methanotrophic sediments (∼195 days) such that the majority of the methane produced within the barrier island aquifer was likely consumed there.

Schutte, C., Wilson, A.M., Evans, T., Moore, W.S. and Joye, S.B. 2017. Deep oxygen penetration drives nitrification in intertidal beach sands. Limnology and Oceanography. (DOI: 10.1002/lno.10731)

Abstract
We discovered a hotspot of elevated nitrate concentration (median = 431 µM) in shallow beach pore water that extended across the entire length of two barrier islands in the southeastern United States of America. We investigated this feature by surveying groundwater geochemistry, measuring fluctuations in in situ dissolved oxygen (DO) concentrations, modeling groundwater flow, and quantifying nitrification rates. Nitrification of groundwater ammonium was the only possible nitrate source, with a measured potential rate of 0.84 µmol m−2 h−1. However, the observed nitrate concentrations were far in excess of the predicted maximum achievable by aerobic nitrification assuming a 2 : 1 ratio of O : N and around 200 µM DO in air-saturated seawater. Groundwater DO concentrations within the hotspot (65 cm depth) were consistently 20–50 µM. The nitrate hotspot was located at the top of the water table beneath dry, undersaturated sand that allowed the penetration of air and the dissolution of excess oxygen into the pore fluids. The total dissolved nitrogen concentration of the hotspot was higher than anywhere else on the island, indicating nitrogen accumulation within the hotspot, most likely via ammonium adsorption. Vertical dispersion was the dominant pathway for nitrate loss from the hotspot. This nitrate was consumed in underlying anoxic sand, coupling microbial pathways of nitrogen oxidation and reduction and removing bioavailable nitrogen from the beach ecosystem.

Segarra, K., Comerford, C., Slaughter, J.B. and Joye, S.B. 2013. Impact of electron acceptor availability on the anaerobic oxidation of methane in coastal freshwater and brackish wetland sediments. Geochimica et Cosmochimica Acta. 115:15 - 30. (DOI: 10.1016/j.gca.2013.03.029)

Abstract
Methane, a powerful greenhouse gas, is both produced and consumed in anoxic coastal sediments via microbial processes. Although the anaerobic oxidation of methane (AOM) is almost certainly an important process in coastal freshwater and salt marsh sediments, the factors that control the rates and pathways of AOM in these habitats are poorly understood. Here, we present the first direct measurements of AOM activity in freshwater (0 PSU) and brackish (25 PSU) wetland sediments. Despite disparate sulfate concentrations, both environments supported substantial rates of AOM. Higher sulfate reduction (SR) rates were measured in the freshwater site and SR at both sites was of sufficient magnitude to support the observed AOM activity. Laboratory incubations of freshwater and brackish tidal, wetland sediments amended with either nothing [control], sulfate, nitrate, manganese oxide (birnessite) or iron oxide (ferrihydrite) and supplied with a methane headspace were used to evaluate the impact(s) of electron acceptor availability on potential AOM rates. Maximum AOM rates in brackish slurries occurred in the sulfate amendments. In contrast, addition of sulfate and several possible electron acceptors to the freshwater slurries decreased AOM rates relative to the control. High ratios of AOM activity relative to SR activity in the nitrate, birnessite, and ferrihydrite treatments of both the brackish and freshwater slurries provided evidence of AOM decoupled from SR. This study demonstrates that both freshwater and brackish coastal wetland sediments support considerable rates of anaerobic methanotrophy and provides evidence for sulfate-independent AOM that may be coupled to nitrate, iron, or manganese reduction in both environments.

Segarra, K., Samarkin, V., King, E., Meile, C. and Joye, S.B. 2013. Seasonal variations of methane fluxes from an unvegetatedtidal freshwater mudflat (Hammersmith Creek, GA). Biogeochemistry. 115:349 - 361. (DOI: 10.1007/s10533-013-9840-6)

Abstract
Wetlands are estimated to contribute nearly 40 % of global annual methane (CH4) emissions to the atmosphere. However, because CH4 fluxes from these systems vary spatially, seasonally, and by wetland type, there is a large uncertainty associated with scaling up the CH4 flux from these environments. We monitored seasonal patterns of CH4 cycling from tidal mudflat wetland sediments adjacent to a vegetated freshwater wetland in coastal Georgia between 2008 and 2009. CH4 emissions were significantly correlated with CH4 production and sediment saturation state with respect to CH4 but not with temperature. CH4 cycling displayed distinct seasonal patterns. Winter months were characterized by low CH4 production and emissions. During the spring, summer and fall, CH4 fluxes exceeded CH4 production in the top 40 cm. Comparison of CH4 sources and sinks in conjunction with the interpretation of CH4 concentration profiles using a 1D reactive transport model indicated that CH4 delivered via lateral tidal pumping likely provided additional CH4 to the upper sediment column. Seasonally high CH4 ebullition rates reflected increased CH4 production and decreased CH4 solubility. The annual CH4 flux was estimated to be on the order of 10 mol CH4 m−2 y−1 which is 2–4 times the global average for wetland CH4 emissions. Thus, even though tidal freshwater mudflats are of limited spatial extent, these environments may serve as globally significant sources of CH4 to the atmosphere. This study highlights the importance of these dynamic environments to the global CH4 cycle and their relevance to climate change.

Seim, H.E., Blanton, J.O. and Elston, S. 2006. Tidal circulation and energy dissipation in a shallow, sinuous estuary. Ocean Dynamics. 56(3-4):360-375. (DOI: 10.1007/s10236-006-0078-x)

Abstract
The tidal dynamics in a pristine, mesotidal (>2 m range), marsh-dominated estuary are examined using moored and moving vessel field observations. Analysis focuses on the structure of the M2 tide that accounts for approximately 80% of the observed tidal energy, and indicates a transition in character from a near standing wave on the continental shelf to a more progressive wave within the estuary. A slight maximum in water level (WL) occurs in the estuary 10–20 km from the mouth. M 2 WL amplitude decreases at 0.015 m/km landward of this point, implying head of tide approximately 75 km from the mouth. In contrast, tidal currents in the main channel 25 km inland are twice those at the estuary mouth. Analysis suggests the tidal character is consistent with a strongly convergent estuarine geometry controlling the tidal response in the estuary. First harmonic (M4) current amplitude follows the M2 WL distribution, peaking at mid-estuary, whereas M4 WL is greatest farther inland. The major axis current amplitude is strongly influenced by local bathymetry and topography. On most bends a momentum core shifts from the inside to outside of the bend moving seaward, similar to that seen in unidirectional river flow but with point bars shifted seaward of the bends. Dissipation rate estimates, based on changes in energy flux, are 0.18–1.65 W m^-2 or 40–175 uW kg^–1. A strong (0.1 m/s), depth-averaged residual flow is produced at the bends, which resembles flow around headlands, forming counter-rotating eddies that meet at the apex of the bends. A large sub-basin in the estuary exhibits remarkably different tidal characteristics and may be resonant at a harmonic of the M2 tide.

Seim, H.E., Blanton, J.O. and Elston, S.A. 2008. The effect of secondary circulation on the salt distribution in a sinuous coastal plain estuary: Satilla River, GA, USA. Continental Shelf Research. 29(1):15-28. (DOI: 10.1016/j.csr.2008.03.018)

Abstract
An analysis of observational data suggests salt exchange in a sinuous coastal plain estuary is significantly impacted by counter-rotating residual horizontal eddies formed by channel curvature in meandering channels. The parts of adjacent eddies that advect material downstream follow the deep part of the channel where the flow continually criss-crosses from one side of the channel to the other and follows a relatively unimpeded trajectory to the sea. On the other hand, the parts of adjacent eddies that advect material upstream cross the channel at a different location where it encounters a series of shoals. In this case, the resulting upstream transport of salt is relatively inefficient and retards the rate at which salt can disperse upstream into the estuary. The strength of these circulations is modulated by the spring/neap cycle, allowing for a stronger gravitational mode of exchange to develop near neap tides, but has minimal impact on the length of the salt intrusion. It is suggested that the impeded upstream salt transport accounts for the observation that an impulse of river discharge advects a given isohaline 10 km downstream in 20 days, but that after the impulse, 70 days are required to return the isohaline to a similar position, counter to the notion of a simple dependence of intrusion length on river discharge.

Seim, H.E., Blanton, J.O. and Gross, T. 2002. Direct stress measurements in a shallow, sinuous estuary. Continental Shelf Research. 22:1565-1578.

Abstract
Observations from a 4 element mooring array collected in a bend of a shallow, sinuous estuary are used to describe the flow, density structure and momentum balance over a 10-day period. In general, the flow in the lower 3 m is stratified on ebb and unstratified on flood and shear is concentrated near the bed on flood and nearly uniform throughout the water column on ebb. At spring tides stratification is reduced and the flows 1 m above bottom (mab) are consistently greatest at the downstream end of the bend. The along-channel density gradient is weakest during spring tides owing to zero gradient over most of ebb flow. At neap tides vertical stratification is strong enough to raise the gradient Richardson number well above 0.25 for most of the ebb tide. Currents are weaker and do not display a regular along-channel pattern. The variation in density and current structure is interpreted to result from variations in crosschannel circulation associated with the channel bend. At spring tides, the cross-channel circulation appears to be strong enough to overturn the water column whereas at neap tides stratification is strong enough to halt the overturning. Reynolds stress measured with a Benthic Acoustic Stress Sensor undergoes a four-fold increase between neap and spring tide. The drag coefficient relative to flow at 1 mab is 0.0015–0.0025. Bed stress in the bend is estimated using this drag coefficient and the maximum instantaneous velocity at 1 mab over the array. Because of the along-channel variability in current speed, the estimated bed stress is roughly twice as large as the measured Reynolds stress in the middle of the bend. The estimated bed stress is found to balance the horizontal pressure gradient and local acceleration, implying that a depth-averaged linear momentum balance adequately describes the dynamics on the bend when the impact of the cross-channel circulation is taken into account in the estimate of the bottom stress.

Sharp, S. and Angelini, C. 2016. Whether disturbances alter salt marsh soil structure dramaticallyaffects Spartina alterniflora recolonization rate. Ecosphere. 7(11):16. (DOI: 10.1002/ecs2.1540)

Abstract
Disturbance regimes are shifting in response to climate change, land-use change, species’ invasions, and other stressors, challenging ecologists to improve understanding of the mechanisms controlling plant recovery under different conditions. In this study, we investigate mechanisms that underpin plant recolonization of two types of disturbance: disturbances that remove standing plant biomass, but leave the underlying soil structure largely intact, and those that remove standing biomass and physically disrupt soil structure. In the southeastern United States, salt marshes, drought and invasive feral hogs (Sus scrofa) are associated with disturbances of these respective types and both leave behind mudflats dotted with patches of cordgrass (Spartina alterniflora), the system’s dominant foundation species. To test how disturbance type and remnant patch size may interact to affect cordgrass recolonization, we transplanted replicate cordgrass patches of three sizes into one mudflat that experienced vegetation-only disturbance (VD) during a recent drought, and a second mudflat where hog activities had disrupted the soil structure creating a soil + vegetation disturbance (soil + VD). Over one year, we monitored plant performance and properties of soil. Compared with the drought-associatedVD where patches, regardless of their size, expanded vigorously, large and medium patches grew little and smaller patches even less in the hog-associated soil + VD mudflat. Moreover while biogeochemical properties varied little in the VD compared with adjacent vegetated marsh areas, the mudflats with soil + VD had less soil-binding organic matter and, hence, were too soft to support crab burrows, leading to a reduction in oxygen availability and cordgrass expansion. These results indicate that cordgrass recovery is far faster from disturbances that do not degrade soil structure than those that do and therefore advocate for disturbance-specific management strategies. Specifically, while transplanting patches is effective in restoring marshes disturbed by drought, wrack, or other factors that leave soil structure intact, preventative measures, like hog population culling, are essential to mitigating the ecological impacts of soil structure-altering disturbances.

Sharp, S. and Angelini, C. 2019. The role of landscape composition and disturbance type in mediating salt marsh resilience to feral hog invasion. Biological Invasions. 21(9):2857-2869. (DOI: 10.1007/s10530-019-02018-5)

Abstract
Habitat patch composition and configuration mediate the fitness and distribution of many species. However, we know little about how this landscape complementation may influence the distribution of an invasive species’ ecological impacts and, in turn, how this affects ecosystem resilience to disturbance. We surveyed > 820 km of coastline to evaluate how landscape complementation mediates patterns in invasive feral hog (Sus scrofa) rooting, trampling and wallowing disturbances in southeastern US salt marshes and assessed marsh resilience to these behaviors in an 8-site survey and 13-month field experiment. We discovered that hog rooting and trampling most often occur where hardwood forest comprises > 30% and salt marsh < 22% of habitat surrounding each surveyed site, respectively, while wallowing correlated most strongly with salt marsh invertebrate densities. At the 8 survey sites, vegetation cover, soil organic carbon, and surface elevation were consistently lower, and soil anoxia and porewater ammonium-nitrogen higher, in hog-disturbed relative to undisturbed areas. The experiment revealed that vegetation can recover when rooted or trampled, but remains depressed when wallowed or repeatedly disturbed. Together, these findings provide novel evidence that habitat patch composition at landscape scales can act together with local habitat attributes to dictate invasive species’ disturbance patterns and highlight areas most vulnerable to invaders. In salt marshes, insights gleaned from such consideration of landscape complementation can inform conservation and management strategies for curbing the impact of this prolific, global invader.

Sheldon, J.E. and Alber, M. 2002. A comparison of residence time calculations using simple compartment models of the Altamaha River estuary, Georgia. Estuaries. 25(6B):1304-1317.

Abstract
The residence and flushing times of an estuary are two different concepts that are often confused. Flushing time is the time required for the freshwater inflow to equal the amount originally present in the estuary. It is specific to fresh water (or materials dissolved in it) and represents the transit time through the entire system (e.g. from head of tide to the mouth). Residence time is the average time particles take to escape the estuary. It can be calculated for any type of material (including fresh water), and will vary depending on the starting location of the material. In the literature, the term residence time is often used to refer to the average freshwater transit time and is calculated as such. We explored these two mixing time scales in the context of the Altamaha River Estuary, Georgia, and present a comparison of techniques for their calculation (fraction of fresh water models and variations of box models). Segmented tidal prism models, another common approach, have data requirements similar to other models but can be cumbersome to implement properly. Freshwater transit time estimates from simple steady-state box models were virtually identical to flushing times for four river-flow cases, as long as boxes were scaled appropriately to river flow, and residence time estimates from box models were also in good agreement. Mixing time estimates from box models were incorrect when boxes were improperly scaled. Mixing time scales vary nonlinearly with river flow, so characterizing the range as well as the mean or median is important for a thorough understanding of the potential for within-estuary processing. We are now developing an improved box model that will allow the calculation of a variety of mixing time scales using simulations with daily variable river discharge.

Sheldon, J.E. and Alber, M. 2006. The calculation of estuarine turnover times using freshwater fraction and tidal prism models: a critical evaluation. Estuaries and Coasts. 29(1):133-146.

Abstract
Freshwater fraction and tidal prism models are simple methods for estimating the turnover time of estuarine water. The freshwater fraction method prominently features flushing by freshwater inflow and has sometimes been criticized because it appears not to include flushing by seawater, but this is accounted for implicitly because the average estuary salinity used in the calculation reflects all the processes that bring seawater into the estuary, including gravitational circulation and tidal processes. The model relies on measurable salinity differences among water masses and so must be used for estuaries with substantial freshwater inflow. Tidal prism models are based on flushing by flood tide inflow and ignore seawater inflow due to gravitational circulation. These models should only be applied to estuaries with weak or nonexistent gravitational circulation, which are generally those with little freshwater inflow. Using a framework that is less ambiguous and more directly applicable to the estimation of turnover times than those used previously, this paper critically examines the application of tidal prism models in well-mixed estuaries with complete tidal exchange, partial ebb return, or incomplete flood mixing and in partially mixed estuaries. Problems with self-consistency in earlier versions of these models also apply to the budgeting procedure used by the LOICZ (Land-Ocean Interactions in the Coastal Zone) program. Although freshwater fraction and tidal prism models are different approaches to estimating turnover times in systems with very different characteristics, consistent derivation shows that these models have much in common with each other and that they yield equivalent values that can be used to make comparisons across systems.

Sheldon, J.E. and Burd, A.B. 2014. Alternating Effects of Climate Drivers on Altamaha River Discharge to Coastal Georgia, USA. Estuaries and Coasts. 37:772–788. (DOI: 10.1007/s12237-013-9715-z)

Abstract
Freshwater delivery is an important factor determining estuarine character and health and may be influenced by large-scale climate oscillations. Variability in freshwater delivery (precipitation and discharge) to the Altamaha River estuary (GA, USA) was examined in relation to indices for several climate signals: the Bermuda High Index (BHI), the Southern Oscillation Index (SOI), the Improved El Nińo Modoki Index (IEMI), the North Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO), and the Pacific/North American Pattern (PNA). Discharge to this estuary has been linked to key ecosystemproperties (e.g., salinity regime, water residence time, nutrient inputs, and marsh processes), so understanding how climate patterns affect precipitation and river discharge will help elucidate how the estuarine ecosystem may respond to climate changes. Precipitation patterns in the Altamaha River watershed were described using empirical orthogonal functions (EOFs) of the combined multidecadal time series of precipitation at 14 stations. The first EOF (67 % of the variance) was spatially uniform, the second EOF (11%) showed a spatial gradient along the long axis of the watershed (NW–SE), and the third EOF (6 %) showed a NE–SWpattern. We compared the principal components (PCs) associated with these EOFs, monthly standardized anomalies of Altamaha River discharge at the gauge closest to the estuary, and the climate indices. Complex, seasonally alternating patterns emerged. The BHI was correlated with June–January discharge and precipitation PC 1. The SOI was correlated with January–April discharge and precipitation PC 2, and also weakly correlated with PC 1 in November–December. The AMO was correlated with river discharge and precipitation PC 3 mainly in December–February and June. The correlation patterns of precipitation PCs with PDO and PNAwere similar to those with SOI, but weaker. There were no consistent relationships with two NAO indices or IEMI. Connections between climate signals and estimates of nutrient loading were consistent with the connections to discharge. The occurrence of tropical storms in the region was strongly related to the BHI but not to the other climate indices, possibly representing the influence of storm tracking more than the rate of storm formation. Comparison with the literature suggests that the patterns found may be typical of southeastern USA estuaries but are likely to be different from those outside the region.

Sheldon, J.E., Griffith, P.C., Peters, F., Sheldon, W.M. Jr., Blanton, J.O., Amft, J. and Pomeroy, L.R. 2012. Southeastern U.S.A. continental shelf respiratory rates revisited. Biogeochemistry. 107:501-506. (DOI: 10.1007/s10533-010-9552-0)

Abstract
Respiratory rates on the U. S. southeastern continental shelf have been estimated several times by different investigators, most recently by Jiang et al. (Biogeochemistry 98:101–113, 2010) who report lower mean rates than were found in earlier work and attribute the differences to analytical error in all methods used in earlier studies. The differences are, instead, attributable to the differences in the geographical scope of the studies. The lower estimates of regional organic carbon flux of Jiang et al. (Biogeochemistry 98:101–113, 2010) are a consequence of their extrapolation of data from a small portion of the shelf to the entire South Atlantic Bight. This comment examines the methodologies used as well as the variability of respiratory rates in this region over space and time.

Silliman, B.R. 2014. Salt marshes. Current Biology. 24(9):348-350. (DOI: 10.1016/j.cub.2014.03.001)

Abstract
Salt marshes are lush, intertidal grasslands renowned for their productivity. The yearly accumulation of plant and animal tissue in salt marshes rivals and often exceeds that observed in other highly productive ecosystems, including coral reefs and tropical rain forests. Although the local diversity of plants and animals found in salt marshes is comparatively low, the abundance of organisms that do occur in marshes is often breathtaking. The abundance per square meter of one species of fiddler crab or snail routinely reaches 100–400 individuals, at times over 1000, and over larger spatial scales the density of one species of non-insect invertebrate (mussels, crabs and snails) can often reach 50,000,000 per square kilometer. Globally, plant species richness in salt marshes is surprisingly high, with over 500 salt marsh plant species known.

Silliman, B.R. and Angelini, C. 2012. Trophic cascades across diverse plant ecosystems. Nature Education Knowledge. 3(9):3.

Abstract
Trophic cascades are powerful indirect interactions that can control entire ecosystems. Trophic cascades occur when predators limit the density and/or behavior of their prey and thereby enhance survival of the next lower trophic level.

Silliman, B.R. and He, Q. 2018. Physical Stress, Consumer Control, and New Theory in Ecology. Trends in Ecology and Evolution. 33(7):492 - 503. (DOI: 10.1016/j.tree.2018.04.015)

Abstract
Consumer–prey interactions form the foundation of food webs and are affected by the physical environment. Multiple foundational theories in ecology [e.g., the environmental stress model (ESM), the stress–gradient hypothesis (SGH), and ecosystem resilience theory] assume increased physical stress dampens top-down control of prey. In the large majority of empirical studies, however, physical stress either does not affect or amplifies consumer control. Additive and synergistic impacts of physical stress on consumer control appear more common, for example, for herbivory versus predation, and for warm- versus cold-blooded consumers. Predictability in how physical stress affects consumer control, however, remains largely unknown. We expand classical theories in ecology so that their assumption about physical stress–consumer control relationships can be inclusive of what primarily occurs in nature.

Silliman, B.R. and Newell, S.Y. 2003. Fungal farming in a snail. Proceedings of the National Academy of Sciences. 100:15643-15648.

Abstract
Mutualisms between fungi and fungus-growing animals are model systems for studying coevolution and complex interactions between species. Fungal growing behavior has enabled cultivating animals to rise to major ecological importance, but evolution of farming symbioses is thought to be restricted to three terrestrial insect lineages. Surveys along 2,000 km of North America's Atlantic coast documented that the marine snail Littoraria irrorata grazes fungus-infected wounds on live marsh grass throughout its range. Field experiments demonstrate a facultative, farming mutualism between Littoraria and intertidal fungi. Snails graze live grass primarily not to feed but to prepare substrate for fungal growth and consume invasive fungi. Fungal removal experiments show that snails and fungi act synergistically to suppress marsh grass production. These results provide a case of fungus farming in the marine environment and outside the class Insecta and reveal a previously undemonstrated ecological mechanism (i.e., facilitation of fungal invasion) by which grazers can exert top-down control of marine plant production.

Silliman, B.R., Diller, J., McCoy, M., Earl, K., von de Koppel, J. and Zimmerman, A. 2012. Degradation and resilience in Louisiana salt marshes following the BP-DHW oil spill. Proceedings of the National Academy of Sciences. 109(28):11234-11239.

Abstract
More than 2 y have passed since the BP–Deepwater Horizon oilspill in the Gulf of Mexico, yet we still have little understanding ofits ecological impacts. Examining effects of this oil spill will generatemuch-needed insight into how shoreline habitats and thevaluable ecological services they provide (e.g., shoreline protection)are affected by and recover from large-scale disturbance.Here we report on not only rapid salt-marsh recovery (high resilience)but also permanent marsh area loss after the BP–DeepwaterHorizon oil spill. Field observations, experimental manipulations, andwave-propagationmodeling reveal that (i) oil coveragewas primarilyconcentrated on the seaward edge of marshes; (ii) there were thresholdsof oil coverage that were associated with severity of salt-marshdamage, with heavy oiling leading to plant mortality; (iii) oil-drivenplant death on the edges of these marshes more than doubled ratesof shoreline erosion, further driving marsh platform loss that is likelyto be permanent; and (iv) after 18 mo, marsh grasses have largelyrecovered into previously oiled, noneroded areas, and the elevatedshoreline retreat rates observed at oiled sites have decreased to levelsat reference marsh sites. This paper highlights that heavy oil coverageon the shorelines of Louisiana marshes, already experiencingelevated retreat because of intense human activities, induced a geomorphicfeedback that amplified this erosion and thereby set limits tothe recovery of otherwise resilient vegetation. It thus warns of theenhanced vulnerability of already degraded marshes to heavy oilcoverage and provides a clear example of how multiple human-inducedstressors can interact to hasten ecosystem decline.

Silliman, B.R., Dixon, P.M., Wobus, C., He, Q., Daleo, P., Hughes, B.B., Rissing, M., Willis, J.M. and Hester, M. 2016. Thresholds in marsh resilience to the Deepwater Horizon oil spill. Scientific Reports. 6(32520). (DOI: 10.1038/srep32520)

Abstract
Ecosystem boundary retreat due to human-induced pressure is a generally observed phenomenon. However, studies that document thresholds beyond which internal resistance mechanisms are overwhelmed are uncommon. Following the Deepwater Horizon (DWH) oil spill, field studies from a few sites suggested that oiling of salt marshes could lead to a biogeomorphic feedback where plant death resulted in increased marsh erosion. We tested for spatial generality of and thresholds in this effect across 103 salt marsh sites spanning ~430 kilometers of shoreline in coastal Louisiana, Alabama, and Mississippi, using data collected as part of the natural resource damage assessment (NRDA). Our analyses revealed a threshold for oil impacts on marsh edge erosion, with higher erosion rates occurring for ~1–2 years after the spill at sites with the highest amounts of plant stem oiling (90–100%). These results provide compelling evidence showing large-scale ecosystem loss following the Deepwater Horizon oil spill. More broadly, these findings provide rare empirical evidence identifying a geomorphologic threshold in the resistance of an ecosystem to increasing intensity of human-induced disturbance.

Silliman, B.R., He, Q., Angelini, C., Smith, C.S., Kirwan, M.L., Daleo, P., Renzi, J.J., Butler, J., Osborne, T.Z., Nifong, J.C. and van de Koppel, J. 2019. Field Experiments and Meta-analysis Reveal Wetland Vegetation as a Crucial Element in the Coastal Protection Paradigm. Current Biology. 29(11):1800-1806. (DOI: 10.1016/j.cub.2019.05.017)

Abstract
Increasing rates of sea-level rise and wave action threaten coastal populations. Defense of shorelines by protection and restoration of wetlands has been invoked as a win-win strategy for humans and nature, yet evidence from field experiments supporting the wetland protection function is uncommon, as is the understanding of its context dependency. Here we provide evidence from field manipulations showing that the loss of wetland vegetation, regardless of disturbance size, increases the rate of erosion on wave-stressed shorelines. Vegetation removal (simulated disturbance) along the edge of salt marshes reveals that loss of wetland plants elevates the rate of lateral erosion and that extensive root systems, rather than aboveground biomass, are primarily responsible for protection against edge erosion in marshes. Meta-analysis further shows that disturbances that generate plant die-off on salt marsh edges generally hasten edge erosion in coastal marshes and that the erosion protection function of wetlands relates more to lateral than vertical edge-erosional processes and is positively correlated with the amount of belowground plant biomass lost. Collectively, our findings substantiate a coastal protection paradigm that incorporates preservation of shoreline vegetation, illuminate key context dependencies in this theory, and highlight local disturbances (e.g., oil spills) that kill wetland plants as agents that can accelerate coastal erosion.

Silliman, B.R., Hughes, B.B., Gaskins, L., He, Q., Tinker, T., Read, A., Nifong, J.C. and Stepp, R. 2018. Are the ghosts of nature’s past haunting ecology today? Current Biology. 28. (DOI: 10.1016/j.cub.2018.04.002)

Abstract
Humans have decimated populations of large-bodied consumers and their functions in most of the world’s ecosystems. It is less clear how human activities have affected the diversity of habitats these consumers occupy. Rebounding populations of some predators after conservation provides an opportunity to begin to investigate this question. Recent research shows that following longterm protection, sea otters along the northeast Pacific coast have expanded into estuarine marshes and seagrasses, and alligators on the southeast US coast have expanded into saltwater ecosystems, habitats presently thought beyond their niche space. There is also evidence that seals have expanded into subtropical climates, mountain lions into grasslands, orangutans into disturbed forests and wolves into coastal marine ecosystems. Historical records, surveys of protected areas and patterns of animals moving into habitats that were former hunting hotspots indicate that — rather than occupying them for the first time — many of these animals are in fact recolonizing ecosystems. Recognizing that many large consumers naturally live and thrive across a greater diversity of ecosystems has implications for setting historical baselines for predator diversity within specific habitats, enhancing the resilience of newly colonized ecosystems and for plans to recover endangered species, as a greater range of habitats is available for large consumers as refugia from climate-induced threats.

Silliman, B.R., McCoy, M., Angelini, C., Holt, R.D., Griffin, J.N. and van de Koppel, J. 2013. Consumer Fronts, Global Change, and Runaway Collapse in Ecosystems. Annual Review of Ecology, Evolution, and Systematics. 44:503 - 538. (DOI: 10.1146/annurev-ecolsys-110512-135753)

Abstract
Consumer fronts occur when grazers or predators aggregate in bands along the edges of a resource. Our review reveals that consumer fronts are a common phenomenon in nature, occur in many different ecosystems, and are triggered by universal mechanisms: External forces locally increase top-down control beyond prey carrying and/or renewal capacity, and resource-dependent movement leads to consumer aggregation along the edge of the remaining prey population. Once formed, consumer fronts move through systems as spatially propagating waves, self-reinforced via intense overexploitation and amplified by density-dependent feedbacks. When consumer fronts are spatially restricted, they generate patchiness. In contrast, when consumer fronts are expansive, they can lead to runaway responses that cause large-scale ecosystem degradation and regime shifts. We conceptualize a synergistic stress hypothesis and model that highlight how coupled intensification of physical stress and enhanced consumer pressure can trigger increased occurrence of consumer fronts and decreased system stability and resilience. With escalating climate change and food-web modification, the physical and biological conditions favoring consumer-front formation will likely become a common feature of many ecosystems.

Silliman, B.R., Mozdzer, C., Angelini, C., Brundage, J., Bakker, J., Esselink, P., van de Koppel, J. and Baldwin, A. 2014. Livestock as a Biological Control Agent for an Invasive Wetland Plant. PeerJ. 2:567. (DOI: 10.7717/peerj.567)

Abstract
Invasive species threaten biodiversity and incur costs exceeding billions of US$. Eradication efforts, however, are nearly always unsuccessful. Throughout much of North America, land managers have used expensive, and ultimately ineffective, techniques to combat invasive Phragmites australis in marshes. Here, we reveal that Phragmites may potentially be controlled by employing an affordable measure from its native European range: livestock grazing. Experimental field tests demonstrate that rotational goat grazing (where goats have no choice but to graze Phragmites) can reduce Phragmites cover from 100 to 20% and that cows and horses also readily consume this plant. These results, combined with the fact that Europeans have suppressed Phragmites through seasonal livestock grazing for 6,000 years, suggest Phragmites management can shift to include more economical and effective top-down control strategies. More generally, these findings support an emerging paradigm shift in conservation from high-cost eradication to economically sustainable control of dominant invasive species.

Silliman, B.R., Schrack, E., He, Q., Cope, R., Santoni, A., van der Heide, T., Jacobi, R. and van de Koppel, J. 2015. Facilitation shifts paradigms and can amplify coastal restoration efforts. PNAS. 112(46):14295 - 14300. (DOI: 10.1073/pnas.1515297112)

Abstract
Restoration has been elevated as an important strategy to reverse the decline of coastal wetlands worldwide. Current practice in restoration science emphasizes minimizing competition between out-planted propagules to maximize planting success. This paradigm persists despite the fact that foundational theory in ecology demonstrates that positive species interactions are key to organism success under high physical stress, such as recolonization of bare substrate. As evidence of how entrenched this restoration paradigm is, our survey of 25 restoration organizations in 14 states in the United States revealed that >95% of these agencies assume minimizing negative interactions (i.e., competition) between outplants will maximize propagule growth. Restoration experiments in both Western and Eastern Atlantic salt marshes demonstrate, however, that a simple change in planting configuration (placing propagules next to, rather than at a distance from, each other) results in harnessing facilitation and increased yields by 107% on average. Thus, small adjustments in restoration design may catalyze untapped positive species interactions, resulting in significantly higher restoration success with no added cost. As positive interactions between organisms commonly occur in coastal ecosystems (especially in more physically stressful areas like uncolonized substrate) and conservation resources are limited, transformation of the coastal restoration paradigm to incorporate facilitation theory may enhance conservation efforts, shoreline defense, and provisioning of ecosystem services such as fisheries production.

Snyder, M., Taillefert, M. and Ruppel, C.D. 2004. Redox zonation at the saline-influenced boundaries of a permeable surficial aquifer: effects of physical forcing on the biogeochemical cycling of iron and manganese. Journal of Hydrology. 296:164-178.

Abstract
Research investigating geochemical changes accompanying subsurface mixing of fresh and saline water has primarily focused on cation exchange and mineral dissolution/precipitation reactions. In this study, we report on redox species zonation at the boundaries of a freshwater lens confined beneath a small, permeable island surrounded by saline marshes and tidal creeks and located on the estuary side of Sapelo Island, Georgia. The spatial and temporal distribution of the chemical species in the aquifer implies that the freshwater lens resists saline intrusion by maintaining constant advection across the salinity gradient. As a result, the biogeochemical processes in this aquifer seem to have reached a quasi steady-state very close to equilibrium. Redox reactions associated with natural organic matter oxidation may also play an important role at the salinity transition. Surprisingly, aerobic respiration and microbial iron reduction seem to be the main pathways for natural organic matter oxidation. Sulfate reduction is not significant despite the high concentration of sulfate available, and manganese oxides are probably chemically reduced by dissolved sulfide and Fe2+. This study is the first to demonstrate that iron and manganese reduction takes place at the salinity transitions bounding both sides of an island freshwater lens and that microbial iron reduction accounts for most of anaerobic respiration of natural organic matter at these transitions.

Soomsdat, N., Griffin, J.N., McCoy, M., Hensel, M.S., Buhler, S., Chejanovski, Z.A. and Silliman, B.R. 2014. Independent and combined effects of multiple predators across ontogeny of a dominant grazer. OIKOS. 123(9):1081-1090. (DOI: 10.1111/oik.01579)

Abstract
Ecosystems host multiple coexisting predator species whose interactions may strengthen or weaken top–down control of grazers. Grazer populations often exhibit size-structure, but the nature of multiple predator effects on suppression of size-structured prey has seldom been explicitly considered. In a southeastern US salt-marsh, we used both field (additive design) and mesocosm (additive-substitutive design) experiments to test the independent and combined effects of two species of predatory crab on the survival and predator-avoidance behavior (i.e. a non-consumptive effect) of both juveniles and adults of a dominant grazing snail. Results showed: 1) juvenile snails were more vulnerable to predation; 2) consumptive impacts of predators were hierarchically nested, i.e. the larger predator consumed both juvenile and adult snails, while the smaller-bodied predator consumed only juvenile snails; 3) there were no emergent multiple predator effects on snail consumption; and 4) non-consumptive effects differed from consumptive effects, with only the large predator inducing predator-avoidance behavior of individuals within either snail ontogenetic class. The smaller predator therefore played a functionally redundant trophic role across the prey classes considered, augmenting and potentially stabilizing trophic regulation of juvenile snails. Meanwhile, the larger predator played a complementary and functionally unique role by both expanding the size-spectrum of prey trophic regulation and non-consumptively altering prey behavior. While our study suggests that nestedness of consumptive interactions determined by predator and prey body sizes may allow prediction of the functional redundancy of particular predator species, it also shows that traits beyond predator body size (e.g. habitat domain) may be required to predict potentially cascading non-consumptive effects. Future studies of multiple predators (and predator biodiversity) should continue to strive towards greater realism by incorporating not only size-structured prey, but also other aspects of resource and environmental heterogeneity typical of natural ecosystems.

Spivak, A.C., Sanderman, J., Bowen, J.L., Canuel, E.A. and Hopkinson, C.S. 2019. Global-change controls on soil-carbon accumulation and loss in coastal vegetated ecosystems. Nature Geoscience. 12:685–692. (DOI: https://doi.org/10.1038/s41561-019-0435-2)

Abstract
Coastal seagrass, mangrove and salt-marsh ecosystems—also termed blue-carbon ecosystems—play an important role in theglobal carbon cycle. Much of the organic carbon they store rests in soils that have accumulated over thousands of years. Rapidly changing climate and environmental conditions, including sea-level rise, warming, eutrophication and landscape development, will impact decomposition and thus the global reservoir of blue soil organic carbon. Yet, it remains unclear how these disturbances will affect the key biogeochemical mechanisms controlling decomposition—mineral protection, redox zonation, water content and movement, and plant–microbe interactions. We assess the spatial and temporal scales over which decomposition mechanisms operate and how their effectiveness may change following disturbances. We suggest that better integration of decomposition mechanisms into blue-carbon models may improve predictions of soil organic carbon stores and facilitate incorporation of coastal vegetated ecosystems into global budgets and management tools.

Spyrakos, E., O'Donnell, R., Hunter, P., Miller, C., Scott, M., Simis, S., Neil, C., Barbarosa, C., Binding, C., Bradt, S., Bresciani, M., Dall'Olmo, G., Giardino, C., Gitelson, A., Kutser, T., Li, L., Matsusguta, B., Martinez-Vicente, V., Matthews, M., Ogashawara, I., Ruiz-Verdu, A., Schalles, J.F., Tebbs, E., Zhang, Y. and Tyler, A. 2017. Optical types of inland and coastal waters. Limnology and Oceanography. (DOI: 10.1 002/lno.10674)

Abstract
Inland and coastal water bodies are critical components of the global biosphere. Timely monitoring is necessary to enhance our understanding of their functions, the drivers impacting on these functions and to deliver more effective management. The ability to observe water bodies from space has led to Earth observation (EO) becoming established as an important source of information on water quality and ecosystem condition. However, progress toward a globally valid EO approach is still largely hampered by inconsistences over temporally and spatially variable in-water optical conditions. In this study, a comprehensive dataset from more than 250 aquatic systems, representing a wide range of conditions, was analyzed in order to develop a typology of optical water types (OWTs) for inland and coastal waters. We introduce a novel approach for clustering in situ hyperspectral water reflectance measurements (n54045) from multiple sources based on a functional data analysis. The resulting classification algorithm identified 13 spectrally distinct clusters of measurements in inland waters, and a further nine clusters from the marine environment. The distinction and characterization of OWTs was supported by the availability of a wide range of coincident data on biogeochemical and inherent optical properties from inland waters. Phylogenetic trees based on the shapes of cluster means were constructed to identify similarities among the derived clusters with respect to spectral diversity. This typification provides a valuable framework for a globally applicable EO scheme and the design of future EO missions.

Stahl, M., Widney, S. and Craft, C.B. 2018. Tidal freshwater forests: Sentinels for climate change. Ecological Engineering. 116:104-109. (DOI: 10.1016/j.ecoleng.2018.03.002)

Abstract
We measured plant community composition and productivity, soil accretion, and C, N, and P burial in a tidal freshwater forest of the Altamaha River, Georgia to gain a better understanding of the ecosystem services they deliver and their ability to keep pace with current and future rates of sea level rise. Ten species were identified in two 0.1 ha plots. Nyssa aquatica (Tupelo Gum) made up 50% of the density and 57% of the total basal area. Nyssa biflora, Liquidambar styraciflua, and Fraxinus pennsylvanica were the next dominant species, collectively accounting for 37% of the density and 26% of the total basal area. Taxodium distichum only accounted for 3% of the density, but 12% of the total basal area. Aboveground productivity, measured as litterfall and stem wood growth, averaged 927 and 1030 g/m2 in 2015 and 2016, respectively, with litterfall accounting for 60% of the total. Tidal forest soils in the streamside and the interior (0–60 cm) contained 3–6% organic C, 0.20–0.40% N, and 270–540 µg/g P. Soil accretion based on 137Cs was 4.0 mm/year on the streamside and 0.2 mm/year in the forest interior. The rate of accretion in the interior is considerably less than the current rate of sea level rise (3.1 mm/year) along the Georgia coast. Because the accretion rate was much higher on the streamside, rates of C sequestration, N and P accumulation, and mineral sediment deposition also were much greater. Low accretion rates in the interior of the forest that accounts for most of the acreage suggests that accelerated sea level rise is likely to lead to foreseeable death of tidal forests from saltwater intrusion and submergence.

Suding, K.N., Collins, S.L., Gough, L., Clark, C.M., Cleland, E.E., Gross, K.L., Milchunas, D.G. and Pennings, S.C. 2005. Functional- and abundance-based mechanisms explain diversity loss due to N fertilization. Proceedings of the National Academy of Sciences, U.S.A. 102:4387-4392.

Abstract
Human activities have increased N availability dramatically in terrestrial and aquatic ecosystems. Extensive research demonstrates that local plant species diversity generally declines in response to nutrient enrichment, yet the mechanisms for this decline remain unclear. Based on an analysis of >900 species responses from 34 N-fertilization experiments across nine terrestrial ecosystems in North America, we show that both trait-neutral and trait-based mechanisms operate simultaneously to influence diversity loss as production increases. Rare species were often lost because of soil fertilization, randomly with respect to traits. The risk of species loss due to fertilization ranged from >60% for the rarest species to 10% for the most abundant species. Perennials, species with N-fixing symbionts, and those of native origin also experienced increased risk of local extinction after fertilization, regardless of their initial abundance. Whereas abundance was consistently important across all systems, functional mechanisms were often system-dependent. As N availability continues to increase globally, management that focuses on locally susceptible functional groups and generally susceptible rare species will be essential to maintain biodiversity.

Sullivan, J.C., Torres, R., Garrett, A., Blanton, J.O., Alexander, C.R. Jr., Robinson, M., Moore, T.C., Amft, J. and Hayes, D. 2015. Complexity in Salt Marsh Circulation for a Semi-enclosed Basin. Journal of Geophysical Research - Earth Surface. (DOI: 10.1002/2014JF003365)

Abstract
The fine details of overmarsh circulation remain largely unexplored and yet they aretypically assumed to control many attributes of salt marsh material cycling, transport and accretion. We characterized the spatial and temporal variability in overmarsh circulation at a 2 km2 Georgia, USA salt marsh using field observations, dye tracer and numerical simulations. The marsh bathymetry was created with a high precision Global Positioning System survey that details the geomorphic structure of intertidal creeks and salt marsh platform features greater than about one meter in width. We assessed flow path dynamics at four spatial scales ranging from 1 m to 1,000 m. Results show the development and decay of simultaneous flow divergence and convergence, concentrated flow and large-scale rotational flow, as well as strong differences between flood and ebb pathways. This current complexity is set by submergence and emergence of subtle salt marsh platform geomorphic structure andit highlights the role of topography in system-wide flow processes.

Tackett, N.W. and Craft, C.B. 2010. Ecosystem development on a coastal barrier island dune chronosequence. Journal of Coastal Research. 26:736-742.

Abstract
Soil and litter organic carbon, nitrogen, and phosphorus were measured across a dune chronosequence on Sapelo Island, Georgia, U.S.A., to characterize ecosystem development and nutrient cycling during primary succession. As successional theory predicts, litter biomass and soil organic matter increased with dune age. The proportion of nutrients contained in the litter also increased with dune age. No litter was present in the grass-dominated foredunes, whereas in the forested dunes litter accounted for 37%, 17%, and 0.11% of the ecosystem (soil plus litter) C, N, and P, respectively. Soil C and N pools increased from the foredunes to older dune classes. Surface soil (0–10 cm) plant-available N (NH +4, N-23) increased from the foredunes to middunes, whereas soil P showed little change with dune age. Nitrogen was highly limiting across the chronosequence. Total soil N ranged from 0.006% (per gram of dry soil) in the foredunes to 0.087% in the middune. Soil N : P was less than 1.3 across all sites, also suggesting N limitation of plant productivity. Plant-available NO23 and total N concentrations in soil and ecosystem (litter plus soil) pools were greater in the middunes, where the N-fixing shrub Morella cerifera was present, than in either the foredunes or forested dunes. Our results suggest that the development of dune nutrient cycles is controlled by both successional age and colonization by N-fixing species.the chronosequence. Total soil N ranged from 0.006% (per gram of dry soil) in the foredunes to 0.087% in the middune.Soil N : P was less than 1.3 across all sites, also suggesting N limitation of plant productivity. Plant-available NO23andtotal N concentrations in soil and ecosystem (litter plus soil) pools were greater in the middunes, where the N-fixingshrub Morella cerifera was present, than in either the foredunes or forested dunes. Our results suggest that thedevelopment of dune nutrient cycles is controlled by both successional age and colonization by N-fixing species.

Takagi, K., Hunter, K.S., Cai, W.-J. and Joye, S.B. 2017. Agents of change and temporal nutrient dynamics in the Altamaha River Watershed. Ecosphere. 8(1):33. (DOI: 10.1002/ecs2.1519)

Abstract
Nutrient and carbon dynamics in river ecosystems are shifting, and climate change is likely a driving factor; however, some previous studies indicate anthropogenic modification of natural resources may supersede the effects of climate. To understand temporal changes in river ecosystems, consideration of how these agents act independently and collectively to affect watershed biogeochemistry is necessary. Through the Georgia Coastal Ecosystems Long-Term Ecological Research Project, we assessed nutrient (phosphorus, nitrogen, silicate) and carbon dynamics, with specific regard to import and export, in the Altamaha River Basin from 2000 to 2012. This is the first study in the region to document the biogeochemical patterns in the Altamaha's four main tributaries, the Little Ocmulgee, Ocmulgee, Oconee, and Ohoopee rivers, and the relationships between biogeochemistry and historical precipitation and discharge patterns as well as agricultural and population census data. As discharge patterns are a primary driver of nutrient loads, we determined that water use was a dominant factor in the shifting ecosystem dynamics. Dissolved inorganic nitrogen loads were primarily driven by population density and dissolved inorganic phosphorus loads were strongly influenced by livestock biomass. Taken together, we conclude that both the transportation and biogeochemical cycling of nutrients within the Altamaha River Watershed were highly impacted by anthropogenic influences, which were then further exacerbated by continued climate change. Furthermore, the N- and P-loads in the Altamaha River and tributaries were dominated by dissolved organic nitrogen and dissolved organic phosphorus, emphasizing a need to further study the bioavailability of these species and the mechanisms driving their potential ecological impacts.

Tallis, H., Lester, S., Ruckelshaus, M., Plummer, M., McLeod, K., Guerry, A., Andelman, S., Caldwell, M., Conte, M., Copps, S., Fox, D., Fujita, R., Gaines, S., Gelfenbaum, G., Gold, B., Kareiva, P., Kim, C., Lee, K., Papenfus, M., Redman, S., Silliman, B.R., Wainger, L. and White, C. 2012. New metrics for managing and sustaining the ocean's bounty. Marine Policy. 36(1):303–306. (DOI: 10.1016/j.marpol.2011.03.013)

Abstract
Policies are arising around the world, most recently in the United States, that mandate the implementation of marine spatial planning as a practical pathway towards ecosystem-based management. In the new United States ocean policy, and several other cases around the globe, ecosystem services are at the core of marine spatial planning, but there is little guidance on how ecosystem services should be measured, making it hard to implement this new approach. A new framework is shown here for practical, rigorous ecosystem service measurement that high lights contributions from both natural and social systems. The novel three-step framework addresses traditional shortcomings of an ecosystem services approach by giving managers and scientists the tools to assess and track: (1) the condition of the ecosystem (supply metrics),(2)the amount of ocean resources actually used or enjoyed by people (service metrics), and (3) people's preference for that level of service (value metrics). This framework will allow real world progress on marine spatial planning to happen quickly, and with a greater chance for success.

Tao, J., Mishra, D., Cotten, D.L., O'Connell, J., Leclerc, M.Y., Nahrawi, H.B., Zhang, G. and Pahari, R. 2018. A Comparison between the MODIS Product (MOD17A2) and a Tide-Robust Empirical GPP Model Evaluated in a Georgia Wetland. Remote Sensing. 10:1831. (DOI: 10.3390/rs10111831)

Abstract
Despite the importance of tidal ecosystems in the global carbon budget, the relationshipsbetween environmental drivers and carbon dynamics in these wetlands remain poorly understood.This limited understanding results from the challenges associated with in situ flux studies andtheir correlation with satellite imagery which can be affected by periodic tidal flooding. Carbondioxide eddy covariance (EC) towers are installed in only a few wetlands worldwide, and thelongest eddy-covariance record from Georgia (GA) wetlands contains only two continuous yearsof observations. The goals of the present study were to evaluate the performance of existingMODIS Gross Primary Production (GPP) products (MOD17A2) against EC derived GPP anddevelop a tide-robust Normalized Difference Moisture Index (NDMI) based model to predict GPPwithin a Spartina alterniflora salt marsh on Sapelo Island, GA. These EC tower-based observationsrepresent a basis to associate CO2 fluxes with canopy reflectance and thus provide the means touse satellite-based reflectance data for broader scale investigations. We demonstrate that Light UseEfficiency (LUE)-based MOD17A2 does not accurately reflect tidal wetland GPP compared to a simpleempirical vegetation index-based model where tidal influence was accounted for. The NDMI-basedGPP model was capable of predicting changes in wetland CO2 fluxes and explained 46% of thevariation in flux-estimated GPP within the training data, and a root mean square error of 6.96 g C m􀀀2in the validation data. Our investigation is the first to create a MODIS-based wetland GPP estimationprocedure that demonstrates the importance of filtering tidal observations from satellite surfacereflectance data.

Tellez, M. and Nifong, J.C. 2014. Gastric nematode diversity between estuarine and inland freshwater populations of the American alligator (Alligator mississippiensis ,daudin 1802), and the prediction of intermediate hosts. International Journal for Parasitology:Parasites and Wildlife. 3:227-235. (DOI: 10.1016/j.ijppaw.2014.07.001)

Abstract
We examined the variation of stomach nematode intensity and species richness of Alligator mississippiensis from coastal estuarine and inland freshwater habitats in Florida and Georgia, and integrated prey content data to predict possible intermediate hosts. Nematode parasitism within inland freshwater inhabiting populations was found to have a higher intensity and species richness than those inhabiting coastal estuarine systems. This pattern potentially correlates with the difference and diversity of prey available between inland freshwater and coastal estuarine habitats. Increased consumption of a diverse array of prey was also correlated with increased nematode intensity in larger alligators. Parasitic nematodesDujardinascaris waltoni, Brevimulticaecum tenuicolle, Ortleppascaris antipini, Goezia sp., and Contracaecum sp. were present in alligators from both habitat types. Dujardinascaris waltoni, B. tenuicolle, and O. antipini had a significantly higher abundance among inland inhabiting alligators than hosts from estuarine populations.Our findings also suggest that host specific nematode parasites of alligators may have evolved to infect multiple intermediate hosts, particularly fishes, crabs, and turtles, perhaps in response to the opportunistic predatory behaviors of alligators

Thompson, V.D. and Andrus, C.F. 2011. Evaluating Mobility, Monumentality, and Feasting at the Sapelo Island Shell Ring Complex. American Antiquity. 76(2):315-343.

Abstract
wo of the most salient anthropological questions regarding southeastern shell ring sites are related to the season(s) that they were occupied and whether or not the deposits represent monumental constructions and/or feasting remains. This paper addresses these questions through the analysis of growth band of clams (Mercenaria spp.) (N = 620) and stable oxygen isotope ratios of clam and oyster shells (Crassostrea virginica) (N = 58) at the Sapelo Island Shell Ring complex located on the Georgia coast, USA. The season of death and the samples 'position in the shell matrix at Sapelo provide important information on the rate of shell deposition and the season(s) the site was occupied. These data support the view that at least some portion of the human population at Sapelo occupied the site year-round. Additionally, while it appears that two shell rings at the site formed through the gradual deposition and accumulation of daily subsistence, other areas evidence short term, large-scale, shellfish processing and may lend credence to the view that at some point shell rings become monuments, commemorating rituals and gatherings.

Thompson, V.D. and Andrus, C.F. 2013. Using Oxygen Isotope Sclerochronology to Evaluate the Role of Small Islands among the Guale of the Georgia Coast, USA. Journal of Island and Coastal Archaeology. 8:190-209. (DOI: 10.1080/15564894.2012.708007)

Abstract
In this article, we present the results of sequential oxygen isotope analysis performed on hard clam, Mercenaria spp. (n = 5) and eastern oyster, Crassostrea virginica (n = 13) valves excavated from Pumpkin Hammock (9MC350). These data are used to evaluate Guale models of settlement and subsistence along the Georgia coast during the late pre-Contact and early Colonial eras (ca. AD 1325 to 1700). Season of collection data indicate shells were collected and deposited on the island during all four seasons, suggesting year-round occupation of the site. In addition, oxygen isotope values imply the Guale exploited mollusks from habitats over a wide range of salinity. We interpret this to signify that the Guale ranged broadly over the coastal landscape and that they were able to exploit these distant resources due to their use of watercraft. Finally, we place these findings within the broader context of the changing social landscape during the late pre-Contact and Colonial eras of the Georgia coast.

Thompson, V.D. and Turck, J.A. 2009. Adaptive Cycles of Coastal Hunter-Gatherers. American Antiquity. 74(2):255-278.

Abstract
Along the southeastern Atlantic coast of Georgia, hunter-gatherer groups substantially altered the landscape for more than three millennia (ca. 4,200―1,000 B.P.) leaving behind a distinct material record in the form of shell rings, middens, and burial mounds. During this time, these groups experienced major changes in sea level and resource distribution. Specifically, we take a resilience theory approach to address these changes and discuss the utility of this theory for archaeology in general. We suggest that despite major destabilizing forces in the form of sea-level lowering and its concomitant effects on resource distribution, cultural systems rebounded to a structural pattern similar to the one expressed prior to environmental disruption. We propose, in part, the ability for people to return to similar patterns was the result of the high visibility of previous behaviors inscribed on the landscape in the form of shell middens and rings from the period preceding environmental disruption. Finally, despite a return to similar cultural formulations, hunter-gatherers experienced some fundamental changes resulting in modifications to existing behaviors (e.g., ringed villages) as well as the addition of new ones in the form of burial-mound construction.

Thompson, V.D. and Turck, J.A. 2010. Island Archaeology and the Native American Economies (2500 B.C.–A.D. 1700) of the Georgia Coast. Journal of Field Archaeology. 35(3):283-297. (DOI: 10.1179/009346910X12707321358991)

Abstract
Our research along the Georgia coast of the southeastern United States explores the role that small islands played in Native American economies over some 4000 years (ca. 2500 B.C.–A.D. 1700). Most archaeological research in the region has concentrated on large barrier islands that front the Atlantic Ocean. Less understood are the much smaller back-barrier islands, also called marsh islands, located in the inter-tidal environment. Our survey of four of these islands, Little Sapelo Island, Pumpkin Hammock, Mary Hammock, and Patterson Island, indicates that such landforms were important for most of the prehistoric and early historical Native American occupations of the coast. These landforms were key components in subsistence systems that relied heavily on estuarine resources. We discuss the implications of our study regarding method and theory in archaeology, and consider long-standing debates as to the productivity of coastal and maritime resources and the notion of insularity in is and archaeology. Specificay, we suggest that, for some regions, small islands facilitate connectivity between areas. Further, the methodological implications of our study suggest that many small islands should be investigated as sites. That is, the nature of activity over the entire landform should be the focus of investigations.

Thompson, V.D., Rick, T., Garland, C.J., Thomas, D.H., Smith, K.Y., Bergh, S., Sanger, M., Tucker, B., Lulewicz, I.H., Semon, A.M., Schalles, J.F., Hladik, C.M., Alexander, C.R. Jr. and Ritchison, B.T. 2020. Ecosystem stability and Native American oyster harvesting along the Atlantic Coast of the United States. Science Advances. 6. (DOI: 10.1126/sciadv.aba9652)

Abstract
The eastern oyster (Crassostrea virginica) is an important proxy for examining historical trajectories of coastal ecosystems. Measurement of ~40,000 oyster shells from archaeological sites along the Atlantic Coast of the United States provides a long-term record of oyster abundance and size. The data demonstrate increases in oyster size across time and a nonrandom pattern in their distributions across sites. We attribute this variation to processes related to Native American fishing rights and environmental variability. Mean oyster length is correlated with total oyster bed length within foraging radii (5 and 10 km) as mapped in 1889 and 1890. These data demonstrate the stability of oyster reefs despite different population densities and environmental shifts and have implications for oyster reef restoration in an age of global climate change.

Thomsen, M.S., Alteiri, A., Angelini, C., Bishop, M., Gribben, G., Lear, G., Schiel, D., Silliman, B.R., South, P., Watson, D., Wernberg, T. and Zotz, G. 2018. Secondary foundation species enhance biodiversity. Nature Ecology and Evolution. 2:634-639. (DOI: 10.1038/s41559-018-0487-5)

Abstract
It has long been recognized that primary foundation species (FS), such as trees and seagrasses, enhance biodiversity. Among the species facilitated are secondary FS, including mistletoes and epiphytes. Case studies have demonstrated that secondary FS can further modify habitat-associated organisms (‘inhabitants’), but their net effects remain unknown. Here we assess how inhabitants, globally, are affected by secondary FS. We extracted and calculated 2,187 abundance and 397 richness Hedges’ g effect sizes from 91 and 50 publications, respectively. A weighted meta-analysis revealed that secondary FS significantly enhanced the abundance and richness of inhabitants compared to the primary FS alone. This indirect facilitation arising through sequential habitat formation was consistent across environmental and experimental conditions. Complementary unweighted analyses on log response ratios revealed that the magnitude of these effects was similar to the global average strength of direct facilitation from primary foundation species and greater than the average strength of trophic cascades, a widely recognized type of indirect facilitation arising through sequential consumption. The finding that secondary FS enhance the abundance and richness of inhabitants has important implications for understanding the mechanisms that regulate biodiversity. Integrating secondary FS into conservation practice will improve our ability to protect biodiversity and ecosystem function.

Thomsen, M.S., McGlathery, K.J., Schwarzschild, A. and Silliman, B.R. 2009. Distribution and ecological role of the non-native macroalga Gracilaria vermiculophylla in Virginia salt marshes. Biological Invasions. 11(10):2303-2316. (DOI: 10.1007/s10530-008-9417-9)

Abstract
Intertidal salt marshes are considered harsh habitats where relatively few stress-resistant species survive. Most studies on non-native species in marshes describe terrestrial angiosperms. We document that a non-native marine macroalga, Gracilaria vermiculophylla, is abundant throughout Virginia’s Atlantic coastline. We sampled eight marshes, characterized by low slopes and by the presence of the tube-building polychaete Diopatra cuprea on adjacent mudflats, which have been shown previously to be associated with G. vermiculophylla. G. vermiculophylla was found in 71% of the sampled quadrats on the border between the mudflat and tall Spartina alterniflora, 51% within the tall S. alterniflora zone, and 12% further inland. We also tagged G. vermiculophylla from two habitats: (1) unattached G. vermiculophylla within marshes and (2) G. vermiculophylla ‘incorporated’ onto D. cuprea tubes on the adjacent mudflats. Of the incorporated thalli, 3–9% ended up in the marsh, demonstrating connectivity between habitats. In addition, 21% of unattached thalli remained for 2 weeks within the marsh, suggesting that entanglement around marsh plants reduces tidal drift. Growth experiments in mesh bags indicate that most of the G. vermiculophylla transferred from the lagoon to the marsh decomposed there, potentially enhancing local nutrient levels. Finally, we document that G. vermiculophylla in marshes had a reduced associated flora and fauna compared to G. vermiculophylla on the adjacent Diopatra mudflats. In conclusion, unattached G. vermiculophylla is abundant along marsh borders in the tall S. alterniflora zone in Virginia, and we hypothesize that this non-native species has significant impacts in terms of marsh habitat complexity, species abundance and diversity, nutrient dynamics, productivity, and trophic interactions.

Thomsen, M.S., Wernberg, T., Alteiri, A., Tuya, F., Gulbransen, D., McGlathery, K.J., Holmer, M. and Silliman, B.R. 2010. Habitat cascades: the conceptual context and global relevance of facilitation cascades via habitat formation and modification. Integrative and Comparative Biology. 50:158-175. (DOI: 10.1093/icb/icq042)

Abstract
The importance of positive interactions is increasingly acknowledged in contemporary ecology. Most research has focused on direct positive effects of one species on another. However, there is recent evidence that indirect positive effects in the form of facilitation cascades can also structure species abundances and biodiversity. Here we conceptualize a specific type of facilitation cascade—the habitat cascade. The habitat cascade is defined as indirect positive effects on focal organisms mediated by successive facilitation in the form of biogenic formation or modification of habitat. Based on a literature review, we demonstrate that habitat cascades are a general phenomenon that enhances species abundance and diversity in forests, salt marshes, seagrass meadows, and seaweed beds. Habitat cascades are characterized by a hierarchy of facilitative interactions in which a basal habitat former (typically a large primary producer, e.g., a tree) creates living space for an intermediate habitat former (e.g., an epiphyte) that in turn creates living space for the focal organisms (e.g., spiders, beetles, and mites). We then present new data on a habitat cascade common to soft-bottom estuaries in which a relatively small invertebrate provides basal habitat for larger intermediate seaweeds that, in turn, generate habitat for focal invertebrates and epiphytes. We propose that indirect positive effects on focal organisms will be strongest when the intermediate habitat former is larger and different in form and function from the basal habitat former. We also discuss how humans create, modify, and destroy habitat cascades via global habitat destruction, climatic change, over-harvesting, pollution, or transfer of invasive species. Finally, we outline future directions for research that will lead to a better understanding of habitat cascades.

Thomsen, M.S., Wernberg, T., Engelen, H., Tuya, F., Vanderklift, M., Holmer, M., McGlathery, K., Arenas, F., Kotta, J. and Silliman, B.R. 2012. A meta-analysis of seaweed impacts on seagrasses: generalities and knowledge gaps. Plos ONE. 7(1).

Abstract
Seagrasses are important habitat-formers and ecosystem engineers that are under threat from bloom-forming seaweeds.These seaweeds have been suggested to outcompete the seagrasses, particularly when facilitated by eutrophication,causing regime shifts where green meadows and clear waters are replaced with unstable sediments, turbid waters, hypoxia,and poor habitat conditions for fishes and invertebrates. Understanding the situations under which seaweeds impactseagrasses on local patch scales can help proactive management and prevent losses at greater scales. Here, we provide aquantitative review of available published manipulative experiments (all conducted at the patch-scale), to test whichattributes of seaweeds and seagrasses (e.g., their abundances, sizes, morphology, taxonomy, attachment type, or origin)influence impacts. Weighted and unweighted meta-analyses (Hedges d metric) of 59 experiments showed generally highvariability in attribute-impact relationships. Our main significant findings were that (a) abundant seaweeds had strongernegative impacts on seagrasses than sparse seaweeds, (b) unattached and epiphytic seaweeds had stronger impacts than‘rooted’ seaweeds, and (c) small seagrass species were more susceptible than larger species. Findings (a) and (c) were ratherintuitive. It was more surprising that ‘rooted’ seaweeds had comparatively small impacts, particularly given that thiscategory included the infamous invasive Caulerpa species. This result may reflect that seaweed biomass and/or shading andmetabolic by-products like anoxia and sulphides could be lower for rooted seaweeds. In conclusion, our results representsimple and robust first-order generalities about seaweed impacts on seagrasses. This review also documented a limitednumber of primary studies. We therefore identified major knowledge gaps that need to be addressed before generalpredictive models on seaweed-seagrass interactions can be build, in order to effectively protect seagrass habitats fromdetrimental competition from seaweeds.

Thomsen, M.S., Wernberg, T., Olden, J., Byers, J., Bruno, J.F., Silliman, B.R. and Schiel, D. 2014. Forty years of experiments on invasive species: are biases limiting our understanding of impacts? NeoBiota. 22:1-22. (DOI: 10.3897/neobiota.22.6224)

Abstract
Invasions by non-native species are a threat to biodiversity because invaders can impact native populations, communities and entire ecosystems. To manage this threat, it is necessary to have a strong mechanistic understanding of how non-native species affect local species and communities. We reviewed 259 published papers (1972–2012) that described field experiments quantifying the impact of aquatic non-native species, to examine whether various types of study biases are limiting this understanding. Our review revealed that invasion impacts had been experimentally quantified for 101 aquatic non-native species, in all major freshwater and marine habitats, on all continents except Antarctica and for most higher taxonomic groupings. Over one-quarter (26%) of studies included tests for impacts on local biodiversity. However, despite this extensive research effort, certain taxa, habitats and regions remain poorly studied. For example, of the over one hundred species examined in previous studies, only one was a marine fish and only six were herbivores. Furthermore, over half (53%) of the studies were from the USA and two-thirds (66%) were from experiments conducted in temperate latitudes. By contrast, only 3% of studies were from Africa and <2% from high latitudes. We also found that one-fifth (20%) of studies were conducted in estuaries, but only 1% from coral reefs. Finally, we note that the standard procedure of pooling or not reporting non-significant treatments and responses is likely to limit future synthetic advancement by biasing meta-analysis and severely limiting our ability to identify non-native species with none or negligible ecological impacts. In conclusion, a future focus on poorly-studied taxa, habitats and regions, and enhanced reporting of results, should improve our understanding and management of impacts associated with aquatic non-native species.

Thomsen, M.S., Wernberg, T., Olden, J., Griffin, J. and Silliman, B.R. 2011. A framework to study the context-dependent impacts of marine invasions. Journal of Experimental Marine Biology and Ecology. 400:322-327. (DOI: 10.1016/j.jembe.2011.02.033)

Abstract
The ecological impacts of marine invasive species vary according to the spatial and temporal scale of analysis, thereby challenging the extraction of generalities about underlying mechanisms. Here, we applied a broad impact framework that addresses this scale-dependency, to test if general drivers of impacts can be identified and quantified from marine invasion experiments. This framework explains variability in impacts according to the unique (specific) and universal (general) attributes of the (1) invasive organism, (2) resident biota, (3) resource levels, and (4) abiotic conditions. In this framework, unique and universal attributes encompass the properties that are either ecologically relevant to only a few specific invasions (e.g. a unique toxin) or to most invasions (e.g. invader density, size, age or longevity), respectively. We reviewed 88 published marine invasion impact experiments, where 18 tested for effects of universal and 11 for unique attributes of the invasive organism (63 tested for presence.absence effects, where these attributes are confounded). A meta-analysis confirmed that the species identity and density (representing a unique and universal attribute, respectively) of the invader significantly predicted impacts. These attributes should, therefore, whenever possible, be treated as separate impact-modifiers. By contrast, very few experiments have tested if universal or unique attributes of the resident biota, the resource levels or the abiotic conditions modify invasion impact. This highlights a major research gap; quantitative syntheses cannot be undertaken until more factorial experiments have manipulated the invasive species and habitat-associated drivers in concert (with .2 treatments per test factor). In conclusion, to facilitate a broader understanding of marine invasion impacts, we advocate that universal and unique impact-components, whenever possible, are treated as separate test entities that should be examined for each of the four impact drivers.

Thomsen, M.S., Wernberg, T., Olden, J., Griffin, J.N. and Silliman, B.R. 2011. A broad framework to organize and compare invasive species impacts. Environmental Research. 111:899-908.

Abstract
Invasive species have transformed local, regional and global biotas; however, few generalities about the mechanisms driving impacts of invaders have emerged. To explain variation in impacts among studies, we propose a broad framework that separates drivers of impacts into universal and unique attributes of the invasive species and the invaded habitat. Universal attributes are relevant to all invasions whereas unique attributes are distinct to a specific invasion. For example, impacts associated with the abundance of any invader or the properties of a specific invader (e.g., a rare toxin) represent a universal and unique impact attribute. Through meta-analyses of aquatic field experiments, we demonstrate the utility of our framework, documenting that both the abundance and the taxonomic identity of the invader significantly influence invasion outcomes for marine and freshwater plant and animal invaders. Our review also highlights that many more experiments are needed to test for universal attributes, such as priority effects, age and size, and how the attributes of the invaded habitat further modify invasion impacts. We hope that our framework will stimulate experimental invasion ecology and begin to reconcile the idiosyncrasies that currently impede the development of a unified framework for invasion impacts.

Thomsen, M.S., Wernberg, T., Tuya, F. and Silliman, B.R. 2009. Evidence for impacts of non-indigenous macroalgae: a meta-analysis of experimental field studies. Journal of Phycology. 45(4):812-819. (DOI: 10.1111/j.1529-8817.2009.00709.x)

Abstract
Invasions by nonindigenous macroalgal species (NIMS) potentially cause severe impacts on native species. We conducted a meta-analysis of 18 field-based manipulative experiments to quantify the direction and magnitude of impacts (Hedges effect size d, hereafter ES). We found significant small-to-medium negative effects on “macrophyte abundance” (cover, biomass of native taxa; EScumulative = −0.30) and medium-to-large negative effects on “macrophyte assemblages” (richness, diversity, total abundance; EScumulative = −0.70). In contrast, EScumulative were not significant for “macrophyte processes” (growth, mortality; EScumulative = −0.39), “animal abundance” (densities; EScumulative = −0.13), or “animal assemblages” (richness, diversity; EScumulative  = 0.75). The nonsignificant effect sizes were characterized by low sample sizes and should be interpreted with caution. Three study-specific effect sizes were particularly large (<−2.0), showing that, in specific cases, impacts can be highly negative. From a conservation perspective, focus could be on such worst-case scenarios. Still, the reported EScumulative are likely biased toward larger effects because only the most conspicuous NIMS have been tested and because nonsignificant results are less likely to be published. To better understand the impacts of NIMS, more manipulative experiments are needed, testing more species and under contrasting environmental conditions. Future studies should include procedural control treatments and report the abundance of the NIMS to avoid ambiguous interpretations. In conclusion, current experimental evidence shows that NIMS have, on average, small-to-large negative impacts on native plant species and assemblages. It is possible that these effects can result in severe consequences when accumulated over long time periods and large spatial scales.

Tilburg, C.E., Seay, J.E., Bishop, T.D., Miller, H.L. III and Meile, C. 2010. Distribution and retention of Petrolisthes armatus in a coastal plain estuary: the role of vertical movement in larval transport. Estuarine Coastal and Shelf Science. 88:260-266. (DOI: 10.1016/j.ecss.2010.04.004)

Abstract
Since transport of planktonic larval stages is essential to population maintenance and expansion of many marine species, we examined the spatial and temporal distribution of Petrolisthes armatus (Gibbes, 1850) larvae and the possible underlying physical and behavioral mechanisms responsible for these distributions using a combination of field observations and numerical modeling. The field study consisted of observations of larval abundance and distribution as well as hydrographic surveys of the Satilla River estuary on the east coast of the USA in August 2006. Larvae were found throughout the water column within the tributaries but primarily at depth in the main river. A numerical model was used to examine the effect of flow and possible larval behavior responsible for the observed distribution and the consequences for larval retention in the estuary. Model results that included downward larval movement agreed with the field observations. This agreement provides support for the hypothesis that P. armatus larvae vertically migrate within the water column, which aids in their retention within the estuary.

Tolar, B., Powers, L.C., Miller, W., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2016. Ammonia oxidation is inhibited by hydrogen peroxide at environmentally-relevant concentrations. Frontiers in Microbiology.

Abstract
Marine Thaumarchaeota were discovered over 20 years ago and although a few isolates from this group are now available for study, we do not yet understand the environmental controls on their growth and distribution. Thaumarchaeotes oxidize ammonia to nitrite, mediating a key step in the global nitrogen cycle, and it is estimated that about 20% of all prokaryotic cells in the ocean belong to this phylum. Despite their almost ubiquitous distribution, marine Thaumarchaeota are rarely abundant in open-ocean surface (<100 m) waters. We tested the hypothesis that this vertical distribution is driven by reactive oxygen species (ROS), specifically H2O2, generated by photochemical and biological processes – ‘indirect photoinhibition’ rather than light inhibition as previously postulated for ammonia-oxidizing Archaea. Here we show that H2O2 can be surprisingly toxic to Thaumarchaeota from the Southern Ocean, with ammonia oxidation inhibited by additions of as little as 10 nM H2O2, while temperate Thaumarchaeota ecotypes were more tolerant. This sensitivity could explain the seasonal disappearance of Thaumarchaeota from polar surface waters and the increase in ammonia oxidation rates with depth commonly observed in marine environments. Our results highlight the need for further physiological studies of Thaumarchaeota, and indicate that ROS sensitivity could be used as a characteristic for dividing the group into meaningful ecotypes.

Tolar, B., Ross, M., Wallsgrove, N.J., Liu, Q., Aluwihare, L.I., Popp, B.N. and Hollibaugh, J.T. 2016. Contribution of ammonia oxidation to chemoautotrophy in Antarctic coastal waters. The ISME Journal. (DOI: 10.1038/ismej.2016.61)

Abstract
There are few measurements of nitrification in polar regions, yet geochemical evidence suggests that it is significant, and chemoautotrophy supported by nitrification has been suggested as an important contribution to prokaryotic production during the polar winter. This study reports seasonal ammonia oxidation (AO) rates, gene and transcript abundance in continental shelf waters west of the Antarctic Peninsula, where Thaumarchaeota strongly dominate populations of ammonia-oxidizing organisms. Higher AO rates were observed in the late winter surface mixed layer compared with the same water mass sampled during summer (mean±s.e.: 62±16 versus 13±2.8 nm per day, t-test P<0.0005). AO rates in the circumpolar deep water did not differ between seasons (21±5.7 versus 24±6.6 nm per day; P=0.83), despite 5- to 20-fold greater Thaumarchaeota abundance during summer. AO rates correlated with concentrations of Archaea ammonia monooxygenase (amoA) genes during summer, but not with concentrations of Archaea amoA transcripts, or with ratios of Archaea amoA transcripts per gene, or with concentrations of Betaproteobacterial amoA genes or transcripts. The AO rates we report (<0.1–220 nm per day) are ~10-fold greater than reported previously for Antarctic waters and suggest that inclusion of Antarctic coastal waters in global estimates of oceanic nitrification could increase global rate estimates by ~9%. Chemoautotrophic carbon fixation supported by AO was 3–6% of annualized phytoplankton primary production and production of Thaumarchaeota biomass supported by AO could account for ~9% of the bacterioplankton production measured in winter. Growth rates of thaumarchaeote populations inferred from AO rates averaged 0.3 per day and ranged from 0.01 to 2.1 per day.

Tolar, B., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2016. Oxidation of urea nitrogen in marine nitrifying communities dominated by Thaumarchaeota. Environmental Microbiology. (DOI: 10.1111/1462-2920.13457)

Abstract
Urea nitrogen has been proposed to contribute significantly to nitrification by marine thaumarchaeotes. These inferences are based on distributions of thaumarchaeote urease genes rather than activity measurements. We found that ammonia oxidation rates were always higher than oxidation rates of urea-derived N in samples from coastal Georgia, USA (means±SEM: 382±35 versus 73±24 nmol L-1 d-1, Mann-Whitney U-test p<0.0001), and the South Atlantic Bight (20±8.8 versus 2.2±1.7 nmol L-1 d-1, p=0.026) but not the Gulf of Alaska (8.8±4.0 versus 1.5±0.6, p>0.05). Urea-derived N was relatively more important in samples from Antarctic continental shelf waters, though the difference was not statistically significant (19.4±4.8 versus 12.0±2.7 nmol L-1 d-1, p>0.05). We found only weak correlations between oxidation rates of urea-derived N and the abundance or transcription of putative Thaumarchaeota ureC genes. Dependence on urea-derived N does not appear to be directly related to pH or ammonium concentrations. Competition experiments and release of 15NH3 suggest that urea is hydrolyzed to ammonia intracellularly, then a portion is lost to the dissolved pool. The contribution of urea-derived N to nitrification appears to be minor in temperate coastal waters, but may represent a significant portion of the nitrification flux in Antarctic coastal waters.

Treplin, M., Pennings, S.C. and Zimmer, M. 2013. Decomposition of leaf litter in a U.S. saltmarsh is driven by dominant species, not species complementarity. Wetlands. 33:83-89. (DOI: 10.1007/s13157-012-0353-1)

Abstract
To add to our understanding of species richness effectson ecosystem processes, we studied the importanceof species complementarity in driving decomposition in asaltmarsh in Georgia, USA. We studied pair-wise interactionsof both detritivores and plant litter species and howthey affect decomposition rates in an experiment located onthe mid-marsh platform. Needle rush, Juncus roemerianus,had 2-3 times higher decomposition rates thancordgrass, Spartina alterniflora, or live oak, Quercusvirginiana. Mixing litter types did not promote decompositionrates. Cordgrass decomposition was 1.5-timeshigher when periwinkles, Littoraria irrorata, were presentthan in detritivore-free controls. In contrast, neithercoffee-bean snails, Melampus bidentatus, nor wharfcrabs, Armases cinereum, increased cordgrass decompositionrates. Mixing detritivore species did not increasecordgrass mass loss beyond expected rates from anadditive model. We conclude that in this system, speciesdo not act complementarily with each other, but thatdecomposition rates are controlled by the dominant speciesof angiosperms and invertebrate detritivores.

Turck, J.A. 2012. Where Were All of the Coastally Adapted People During the Middle Archaic Period in Georgia, USA? Journal of Island and Coastal Archaeology. 7:404–424. (DOI: 10.1080/15564894.2011.652763)

Abstract
A dramatic increase in the number of sites, compared to previous periods, has been noted for the Late Archaic (4200-3100 BP) period on the Georgia coast. This presumably larger and more sedentary population has been attributed to sea-level rise and the establishment of the marsh-estuarine system and its resources. To assess this idea, and to understand the conditions prior to the explosion of Late Archaic sites on the coast, a model of sea-level history and attendant landscape changes leading up to the Late Archaic period is created for McIntosh County, Georgia, USA. According to the model, conditions were sufficient for marsh formation prior to the Late Archaic period, suggesting that terminal Middle Archaic (~5000 cal BP) populations should have been established on the coast of Georgia. The fact that no sites dating to this period have been found further suggests that the explosion of Late Archaic period sites in the coastal zone of Georgia may have been due to a colonizing group of people who migrated in from another area.

Turck, J.A. and Thompson, V.D. 2016. Revisiting the resilience of Late Archaic hunter-gatherers along the Georgia coast. Journal of Anthropological Archaeology. 43:39-55. (DOI: 10.1016/j.jaa.2016.05.006)

Abstract
This paper addresses fisher-hunter-gatherer settlement and subsistence variability of the Georgia Coast during the Archaic-Woodland transition, framed within ideas derived from Resilience Theory, and focusing on systemic shifts, or “collapse.” A critical examination of these shifts is needed to understand how communities experience change differentially, which in turn can lead to differential community resilience. Analysis of site file and radiocarbon date databases, as well as Bayesian modeling on a subset of dates, was performed at multiple scales and within distinct micro-environmental habitats. Results indicate that as sea levels dropped, there was continuity in Late Archaic occupation within deltaic areas of the coast, with intensive shellfishing occurring earlier (∼5000 cal. BP) and lasting longer (∼3500 cal. BP). In certain habitats, occupation may have continued into the following Early Woodland period. In non-deltaic areas, shellfishing occurs between 4500 and 3800 cal. BP, followed by subsistence changes and population movement. However, some of the post-3800 cal. BP occupations were fairly substantial. This differential experience of change between deltaic and non-deltaic areas was not accompanied by collapse: both areas had resilient communities. We conclude that inter-village relationships developed during the early Late Archaic period continued into the terminal portion, leading to resilience in the face of change.

van der Heide, T., Govers, L.L., de Fouw, J., Olff, H., van der Geest, M., van Katwijk, M.M., Piersma, T., van de Koppel, J., Silliman, B.R., Smolders, A.J.P. and van Gils, J.A. 2012. A three-stage symbioses forms the foundation of seagrass ecosystems. Science. 319:321-323.

Abstract
Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis,a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve–sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters andoffer new prospects for seagrass ecosystem conservation.

van der Zee, E.M., Angelini, C., Govers, L.L., Christianen, M.J., Alteiri, A., van der Reijden, K.J., Silliman, B.R., van de Koppel, J., van der Geest, M., van Gils, J.A., van der Veer, H.W., Piersma, T., de Ruiter, P.C., Olff, H. and van der Heide, T. 2016. How habitat-modifying organisms structure the food web of two coastal ecosystems. Proc. R. Soc. B. 283(1826):9. (DOI: 10.1098/rspb.2015.2326)

Abstract
The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity.

Vedogbeton, H. and Johnston, R.J. 2020. Commodity Consistent Meta&#8209;Analysis of Wetland Values: An Illustration for Coastal Marsh Habitat. Environmental and Resource Economics. (DOI: https://doi.org/10.1007/s10640-020-00409-0)

Abstract
Prior meta-regression models (MRMs) of wetland values pool value estimates associated with diverse commodity types—for example recreation, flood control, nutrient cycling, habitat provision, nonuse value, and carbon sequestration. Neither theory nor economic intuition justify the inclusion of such dissimilar commodities within a single meta-analytic value function, leading to validity concerns. This article seeks to advance methods for commodity and welfare consistent MRMs, applied to a particular category of wetland values. We develop a wetland value MRM restricted to a specific wetland type (coastal marshes), general location (US and Canada), commodity type (habitat provision and services), and valuation approach (stated preference methods). Results indicate that willingness to pay per household for marsh habitat changes is responsive to scope, spatial scale, market extent,the type of habitat change, household characteristics, and other factors suggested by theory and intuition. Results supersede those of prior wetland value MRMs in terms of statistical performance, estimation of anticipated value surface patterns, and capacity to support conceptually valid benefit transfers. Comparison with an otherwise identical but less commodity consistent MRM demonstrates that commodity consistency leads to improved statistical and benefit transfer performance.

Verity, P.G., Alber, M. and Bricker, S.B. 2006. Development of Hypoxia in Well-mixed Subtropical Estuaries in the Southeastern USA. Estuaries and Coasts, 29(4):665–673.

Abstract
Estuaries throughout much of the South Atlantic Bight (southeastern U.S.) have been considered to be relatively pristine, but are now experiencing elevated concentrations of both organic and inorganic nutrients. As is true in many parts of the world, this eutrophication is correlated with coastal population growth. These estuaries have been assumed to be immune from extended hypoxia, in large part because they are well mixed and do not generally exhibit the water column stratification that is traditionally associated with low concentrations of dissolved oxygen. Data presented here show long-term (19 yr) decreases in dissolved oxygen in surface waters of the Skidaway estuary, a pattern that is occurring throughout coastal Georgia. More limited data from bottom waters exhibit the same trend. The decreases in dissolved oxygen occurred at the same time as observed increases in inorganic and organic nutrients and in bacteria concentrations, implying an increase in heterotrophic activity. These observations suggest that traditional paradigms long applied to stratified estuaries, wherein the cycle that leads to hypoxia is initiated by the uptake of inorganic nutrients by autotrophs that are then decomposed below the pycnocline, may need revision for well-mixed estuaries. Heterotrophic community metabolism, stimulated by anthropogenic loading of organic and inorganic nutrients, can overwhelm even vigorous vertical mixing and horizontal exchange to gradually cause declining oxygen concentrations and eventually hypoxia.

Vinent, O.D., Johnston, R.J., Kirwan, M., Leroux, A. and Martin, V. 2019. Coastal dynamics and adaptation to uncertain sea level rise: Optimal portfolios for salt marsh migration. Journal of Environmental Economics and Management. (DOI: https://doi.org/10.1016/j.jeem.2019.102262)

Abstract
The sustainability of dynamic natural systems often depends on their capacity to adapt to uncertain climate-related changes, where different management options may be combined to facilitate this adaptation. Salt marshes exemplify such a system. Marsh sustainability under rapid sea level rise requires the preservation of transgression zones - undeveloped uplands onto which marshes migrate. Whether these uplands eventually become marsh depends on uncertain sea level rise and natural dynamics that determine migration onto different land types. Under conditions such as these, systematically diversified management actions generally outperform ad hoc or non-diversified alternatives. This paper develops the first adaptation portfolio model designed to optimize the benefits of a migrating coastal system. Results are illustrated using a case study of marsh conservation in Virginia, USA. Results suggest that models of this type can enhance adaptation benefits beyond those available through current approaches.

von de Koppel, J., van der Heide, J., Alteiri, A., Eriksson, B., Bouma, H., Olff, H. and Silliman, B.R. 2015. Long-distance interactions regulate the structure and resilience of coastal ecosystems. Annual Review of Marine Science. 7:139–158. (DOI: 10.1146/annurev-marine-010814-015805)

Abstract
Mounting evidence indicates that spatial interactions are important in structuring coastal ecosystems. Until recently, however, most of this work has been focused on seemingly exceptional systems that are characterized by regular, self-organized patterns. In this review, we document that interactions that operate at long distances, beyond the direct neighborhood of individual organisms, are more common and have much more far-reaching implications for coastal ecosystems than was previously realized. We review studies from a variety of ecosystem types—including cobble beaches, mussel beds, coral reefs, seagrass meadows, and mangrove forests—that reveal a startling interplay of positive and negative interactions between habitats across distances of up to a kilometer. In addition to classical feeding relations, alterations of physical conditions constitute an important part of these long-distance interactions. This entanglement of habitats has crucial implications for how humans manage coastal ecosystems, and evaluations of anthropogenic impact should explicitly address long-distance and system-wide effects before we deem these human activities to be causing little harm.

Vorobev, A., Sharma, S., Yu, M., Lee, J., Washington, B., Whitman, W., Ballantyne, F., Medeiros, P.M. and Moran, M.A. 2018. Identifying labile DOM components in a coastal ocean through depleted bacterial transcripts and chemical signals. Environmental Microbiology. 20:3012-3030. (DOI: 10.1111/1462-2920.14344)

Abstract
Understanding which compounds comprising the complex and dynamic marine dissolved organic matter (DOM) pool are important in supporting heterotrophic bacterial production remains a major challenge. We eliminated sources of labile phytoplankton products, advected terrestrial material and photodegradation products to coastal microbial communities by enclosing water samples in situ for 24 h in the dark. Bacterial genes for which expression decreased between the beginning and end of the incubation and chemical formulae that were depleted over this same time frame were used as indicators of bioavailable compounds, an approach that avoids augmenting or modifying the natural DOM pool. Transport‐ and metabolism‐related genes whose relative expression decreased implicated osmolytes, carboxylic acids, fatty acids, sugars and organic sulfur compounds as candidate bioreactive molecules. FT‐ICR MS analysis of depleted molecular formulae implicated functional groups ~ 30–40 Da in size cleaved from semi‐polar components of DOM as bioreactive components. Both gene expression and FT‐ICR MS analyses indicated higher lability of compounds with sulfur and nitrogen heteroatoms. Untargeted methodologies able to integrate biological and chemical perspectives can be effective strategies for characterizing the labile microbial metabolites participating in carbon flux.

Vu, H. and Pennings, S.C. 2018. Predators mediate above- vs belowground herbivory in a salt marsh crab. Ecosphere. 9(2):e02107. (DOI: 10.1002/ecs2.2107)

Abstract
Predators can significantly affect prey by removing prey individuals and by changing preybehavior. The tradeoff between foraging behavior and predation risk may result in a trophic cascade that can have important effects on ecosystem processes. For herbivores that can feed both above- and belowground, it is likely that predation risk affects the location of feeding. We tested whether two species of predatory marsh crabs affected feeding behavior of the herbivorous crab, Sesarma reticulatum. We found that predatory crabs could kill or injure Sesarma and that Sesarma did less damage to its food plant Spartina alterniflora in the presence of the more dangerous predator. Sesarma prefers to feed on and grows better on belowground rhizomes than aboveground leaves; however, the costs of digging burrows to access rhizomes lead to higher mortality if it is the only diet option. The location of feeding did not affect total biomass of S. alterniflora. For Sesarma, a choice in feeding location allows the crabs the behavioral flexibility to balance the risks of predation, the nutritional benefit of feeding belowground, and the survival costs of belowground feeding. Similar tradeoffs are likely to increase the success of other herbivores that can feed both above- and belowground.

Vu, H., Wieski, K. and Pennings, S.C. 2017. Ecosystem engineers drive creek formation in salt marshes. Ecology. 98(1):162-174.

Abstract
Ecosystem engineers affect different organisms and processes in multiple ways atdifferent spatial scales. Moreover, similar species may differ in their engineering effects forreasons that are not always clear. We examined the role of four species of burrowing crabs(Sesarma reticulatum, Eurytium limosum, Panopeus herbstii, Uca pugnax) in engineering tidalcreek networks in salt marshes experiencing sea level rise. In the field, crab burrows were associatedwith heads of eroding creeks and the loss of plant (Spartina alterniflora) stems. S. reticulatumwas closely associated with creek heads, but densities of the other crab species did notvary across marsh zones. In mesocosm experiments, S. reticulatum excavated the most soil andstrongly reduced S. alterniflora biomass. The other three species excavated less and did notaffect S. alterniflora. Creek heads with vegetation removed to simulate crab herbivory grewsignificantly faster than controls. Percolation rates of water into marsh sediments were 10 timesfaster at creek heads than on the marsh platform. Biomass decomposed two times faster atcreek heads than on the marsh platform. Our results indicate that S. reticulatum increases creekgrowth by excavating sediments and by consuming plants, thereby increasing water flow anderosion at creek heads. Moreover, it is possible that S. reticulatum burrows also increase creekgrowth by increasing surface and subsurface erosion, and by increasing decomposition of organicmatter at creek heads. Our results show that the interaction between crab and plantecosystem engineers can have both positive and negative effects. At a small scale, in contrast toother marsh crabs, S. reticulatum harms rather than benefits plants, and increases erosion ratherthan marsh growth. At a large scale, however, S. reticulatum facilitates the drainage efficiencyof the marsh through the expansion of tidal creek networks, and promotes marsh health.

Wang, S., Di Iorio, D., Cai, W.-J. and Hopkinson, C.S. 2018. Inorganic carbon and oxygen dynamics in a marsh-dominated estuary. Limnology and Oceanography. 63(1):47-71. (DOI: 10.1002/lno.10614)

Abstract
We conducted a free-water mass balance-based study to address the rate of metabolism and net carbon exchange for the tidal wetland and estuarine portion of the coastal ocean and the uncertainties associated with this approach were assessed. We measured open water diurnal O2 and dissolved inorganic carbon (DIC) dynamics seasonally in a salt marsh-estuary in Georgia, U.S.A. with a focus on the marsh-estuary linkage associated with tidal flooding. We observed that the overall estuarine system was a net source of CO2 to the atmosphere and coastal ocean and a net sink for oceanic and atmospheric O2. Rates of metabolism were extremely high, with respiration (43 mol m−2 yr−1) greatly exceeding gross primary production (28 mol m−2 yr−1), such that the overall system was net heterotrophic. Metabolism measured with DIC were higher than with O2, which we attribute to high rates of anaerobic respiration and reduced sulfur storage in salt marsh sediments, and we assume substantial levels of anoxygenic photosynthesis. We found gas exchange from a flooded marsh is substantial, accounting for about 28% of total O2 and CO2 air–water exchange. A significant percentage of the overall estuarine aquatic metabolism is attributable to metabolism of marsh organisms during inundation. Our study suggests not rely on oceanographic stoichiometry to convert from O2 to C based measurements when constructing C balances for the coastal ocean. We also suggest eddy covariance measurements of salt marsh net ecosystem exchange underestimate net ecosystem production as they do not account for lateral DIC exchange associated with marsh tidal inundation.

Wang, Y., Castelao, R. and Di Iorio, D. 2017. Salinity Variability and Water Exchange in Interconnected Estuaries. Estuaries and Coasts. (DOI: 10.1007/s12237-016-0195-9)

Abstract
A high-resolution coastal ocean model is used to investigate salinity variability and water exchange in a complex coastal system off the southern U.S. characterized by three adjacent sounds that are interconnected by a network of channels, creeks, and intertidal areas. Model results are generally highly correlated with observations from the Georgia Coastal Ecosystem Long Term Ecological Research(GCE-LTER) program, revealing a high degree of salinity variability at the Altamaha River and Doboy Sound, decreasing sharply to ward Sapelo Sound. A Lagrangian particle tracking method is used to investigate local residence time and connectivity in the system. Local residence time is highly variable, increasing with distance from the Altamaha River and decreasing with river flow, revealing that discharge plays a dominant role on transport processes and estuary-shelf ex-change. The Altamaha River and Doboy Sound are connected to each other in all seasons, with exchange occurring both via coastal and estuarine pathways. While particles released at the Altamaha and Doboy rarely reach Sapelo Sound, particles released at Sapelo Sound and the creeks surrounding its main channel can reach the entire estuarine system.

Wang, Z. and Cai, W.-J. 2004. Carbon dioxide degassing and inorganic carbon export from a marsh dominated estuary (the Duplin River): A marsh CO2 pump. Limnology & Oceanography. 49(2):341-352.

Abstract
We investigated the seasonal changes and the interactions of the CO2 system in a marsh-dominated estuary, the Duplin River, on Sapelo Island, Georgia. Surface water pCO2, total alkalinity (TA), and total dissolved inorganic carbon (DIC) showed a pronounced seasonal progression in this system. The estuary released 256–306 g C m^-2 (of water) yr^-1 of CO2 to the atmosphere and exported 109 g C m^-2 (of water) yr^-1 of DIC to adjacent coastal waters. There was a clear seasonal pattern in both fluxes with spring minima, and late summer and fall maxima. Release of inorganic carbon as a respiratory product from surrounding salt marshes is the primary process supporting these two carbon export terms. Concurrently, TA was exported from the Duplin River mainly in summer and fall as a result of anaerobic respiration in marshes. Based on data from the upper Duplin River, export of inorganic carbon from salt marshes was 156 g C m^-2 (of marsh) yr^-1. Extrapolation of this value to all southeastern U.S. salt marshes indicates that they cumulatively export 0.7 x 10^12 g inorganic carbon annually to coastal waters. This export rivals that of riverine inorganic carbon flux. We propose that the CO2 fixation of marsh grasses and the subsequent export of inorganic and organic carbon is one major mechanism that causes the marsh-influenced nearshore and offshore waters in the southeastern U.S. to be annual net sources of atmospheric CO2. We also suggest that this process provides an efficient and unique means for ocean carbon sequestration of atmospheric CO2.

Wang, Z., Cai, W.-J., Wang, Y. and Ji, H. 2005. The southeastern continental shelf of the United States as an atmospheric CO2 source and an exporter of inorganic carbon to the ocean. Continental Shelf Research 25:1917-1941.

Abstract
The US southeastern continental shelf, also known as the South Atlantic Bight (SAB), is a strong source of CO2 to the atmosphere, which is in direct contrast to recent reports regarding other major continental shelves. Both spatial (cross-shelf) and seasonal variations of the CO2 system were pronounced in the SAB. Sea surface pCO2 in winter was undersaturated relative to the atmosphere, while oversaturation of pCO2 dominated the entire shelf water in all other seasons. Annually, the SAB releases CO2 to the atmosphere at an average rate of 30 g Cm^-2 (2.5 mol Cm^-2). This system also discharges dissolved inorganic carbon to the open ocean (30 g Cm^-2 yr^-1). Methods of estimating CO2 flux and DIC flux are critically evaluated and compared. A carbon mass balance model in the SAB is presented based on inorganic carbon .uxes from this study and organic carbon .uxes from literature. The carbon budget is much closer to balance by using this carbon .ux approach than by direct measurements of primary production and respiration. It is concluded that the SAB is a net heterotrophic system annually. Intensi.ed heating, elevated input of inorganic carbon from coastal salt marshes, microbial respiration of marsh-exported organic carbon and the lack of annual spring blooms all contribute to maintaining the SAB as a strong CO2 source to the atmosphere during the warm seasons. In winter, the primary factor that governs the CO2 sink in the SAB is likely the cooling process. Strong heterotrophy during warm seasons also sustains the SAB to be an exporter of inorganic carbon to the open ocean annually. The SAB shelf functions differently from the East China Sea, the North Atlantic European Shelves, and the Mid-Atlantic Bight as a source or sink of atmospheric CO2. The SAB is classified as a "marsh-dominated" shelf as compared to other shelves in terms of carbon dynamics. Further work to study carbon dynamics in coastal margins is warranted to interpret their roles in the global CO2 budget.

Wang, Z.A., Cai, W.-J., Wang, Y. and Upchurch, B.L. 2003. A long pathlength liquid-core waveguide sensor for real-time pCO2 measurements at sea. Marine Chemistry. 84:73–84.

Abstract
An improved spectrophotometric pCO2 sensor based on a long pathlength liquid-core waveguide is described for pCO2 underway measurements. A low refractive index (RI) amorphous fluoropolymer (Teflon AF 2400) tubing, the heart of the sensor, served as both a CO2-permeable membrane equilibrator and a long pathlength liquid-core waveguide spectrophotometric cell. By using absorbance ratios at three wavelengths and carefully preparing and storing indicator solution, good reproducibility and long-term stability were achieved. The sensor behaved closely to theoretical prediction. Two pronounced features of the sensor were fast response (approximately 2 min to reach 99% of full response) due to high permeability of the Teflon AF, and high precision (about +/- 2–3 microatm in the pCO2 range of 200–500 microatm) due to the long pathlength. The temperature dependence of the sensor is also discussed. The sensor’s measurements agreed well with the "showerhead equilibrator plus infrared detector" method during an underway survey of sea surface pCO2 along a transect off the Georgia coast in December 2000. Besides underway mapping, the sensor shows broad applicability for measuring pCO2 in different environments.

Wason, E.L. and Pennings, S.C. 2008. Grasshopper (Orthoptera: Tettigoniidae) species composition and size across latitude in Atlantic Coast salt marshes. Estuaries and Coasts. 31:335-343.

Abstract
Although grasshoppers are common salt marsh herbivores, we know little about geographic variation in their species composition. We documented latitudinal variation in species composition of the tettigoniid grasshopper fauna of Atlantic Coast salt marshes. Tettigoniids (N=740 adults) were collected from the Spartina alterniflora zone of 31 salt marsh sites across a latitudinal range of 13.19° (Florida to Maine), with an additional 52 individuals collected from the Juncus roemerianus zone of low-latitude marshes for comparative purposes. Eight species were collected, but some were common only at a few sites or rare throughout the entire collection range. The tettigoniid community was dominated by Orchelimum fidicinium at low latitudes and Conocephalus spartinae at high latitudes. Several factors might explain this shift, including changes in climate, plant phenology, and plant zonation patterns. O. fidicinium and C. spartinae increased in body size toward low latitudes. In laboratory feeding assays, O. fidicinium readily ate S. alterniflora and J. roemerianus leaves, Orchelimum concinnum, which is largely restricted to the J. roemerianus zone, ate only J. roemerianus leaves, and Conocephalus spp. ate neither, consistent with literature suggestions that they mainly consume seeds and flowers.

Wenner, E., Knott, D., Barans, C., Wilde, S., Blanton, J.O. and Amft, J. 2005. Key factors influencing the transport of white shrimp (Litopenaeus setiferus) post-larvae into the Ossabaw Sound System, Georgia, USA. Fisheries Oceanography. 14:175-194. (DOI: 10.1111/j.1365-2419.2005.00328.x)

Abstract
We examined conditions under which white shrimp (Litopenaeus setiferus) post-larvae enter an estuarine channel receiving high freshwater discharge and one receiving negligible discharge in the Ossabaw Sound system of Georgia, USA, during 1997 and 1998. We used surface nets to collect plankton over several 14-day periods, during which consecutive tows were made at night against the flooding current at stations in the inlet channels. During these sampling periods, additional intensive periods of around-the-clock surface and near-bottom (using a bottom sled) plankton tows were made. Data on oceanographic conditions were obtained from moored instrument arrays and shipboard sampling. We identified three key factors that influenced the densities of post-larval white shrimp in time and space within the Ossabaw inlet system. The first factor was a critical minimum temperature of coastal waters of 27–28°C. Once the threshold temperature was reached, lunar tidal stage became a key factor when the full duration of the flood tide coincided with darkness during peak ingress. This peak also coincided with an increase in water level within the system by more than 0.2 m, which induced an additional influx of water that reinforces the flood current over the ingress period. Our results suggest that the direction of subtidal currents (into or out of the system) becomes a significant factor in post-larval ingress when influx of water coincides with the time of favorable temperature conditions and nighttime flood tides.

Weston, N.B. and Joye, S.B. 2005. Temperature-driven decoupling of key phases of organic matter degradation in marine sediments. Proceedings of the National Academy of Sciences (USA). 102(47):17036-17040.

Abstract
The long-term burial of organic carbon in sediments results in the net accumulation of oxygen in the atmosphere, thereby mediating the redox state of the Earth's biosphere and atmosphere. Sediment microbial activity plays a major role in determining whether particulate organic carbon is recycled or buried. A diverse consortium of microorganisms that hydrolyze, ferment, and terminally oxidize organic compounds mediates anaerobic organic matter mineralization in anoxic sediments. Variable temperature regulation of the sequential processes, leading from the breakdown of complex particulate organic carbon to the production and subsequent consumption of labile, low-molecular weight, dissolved intermediates, could play a key role in controlling rates of overall organic carbon mineralization. We examined sediment organic carbon cycling in a sediment slurry and in flow through bioreactor experiments. The data show a variable temperature response of the microbial functional groups mediating organic matter mineralization in anoxic marine sediments, resulting in the temperature-driven decoupling of the production and consumption of organic intermediates. This temperature-driven decoupling leads to the accumulation of labile, low-molecular weight, dissolved organic carbon at low temperatures and low-molecular weight dissolved organic carbon limitation of terminal metabolism at higher temperatures.

Weston, N.B., Dixon, R.E. and Joye, S.B. 2006. Ramifications of increased salinity in tidal freshwater sediments: Geochemistry and microbial pathways of organic matter mineralization. Journal of Geophysical Research. 111:G01009. (DOI: 10.1029/2005JG000071)

Abstract
The effects of salinity intrusion on the anaerobic microbial and geochemical dynamics of tidal freshwater sediments were investigated using flow-through sediment reactors. In freshwater control sediments, organic matter mineralization was dominated by methanogenesis (62%), followed by sulfate reduction (18%), denitrification (10%), and iron reduction (10%). Upon salinity intrusion, nutrient (ammonium, silicate, phosphate) concentrations increased and rates of methanogenesis declined. Iron-oxide bioavailability increased and microbial iron reduction appeared to account for >60% of organic matter oxidation for several days after salinity intrusion. However, sulfate reduction was the dominant pathway (>50%) of organic matter oxidation within 2 weeks of salinity intrusion, and accounted for >95% of total organic matter mineralization after 4 weeks. Total in situ sediment organic matter mineralization doubled following salinity intrusion. Increased nutrient release, decreased methanogenesis and a rapid shift to sulfate reduction, with a coincident increase overall organic matter mineralization, accompanied salinity intrusion into previously freshwater riverine sediments.

Weston, N.B., Hollibaugh, J.T. and Joye, S.B. 2009. Population growth away from the coastal zone: Thirty years of land use change and nutrient export from the Altamaha River, GA. Science of the Total Environment. 407:3347-3356. (DOI: 10.1016/j.scitotenv.2008.12.066)

Abstract
We used more than thirty years of water quality monitoring data collected by the United States Geological Survey at several stations in the Altamaha River and its tributaries to examine the relationship between population density, agricultural land use, and nutrient export from the watershed. Population densities in the Altamaha River watershed increased during the study period, most notably in the upper watershed near metropolitan Atlanta, while agricultural land use declined throughout the watershed. NOx, TN and P in rivers were related to human population densities, while OC and NH+4 concentrations in rivers were apparently related to agricultural land use. A general pattern of increasing NOx and TN and decreasing NH4+, P and OC over time throughout the watershed reflected changing population and land use. The overall average load from the Altamaha River to the coastal zone during the study period was 1.1, 5.6,16.9,0.9 and 262 kmol km-2 yr-1, delivering 40,197, 596, 30, and 9213 106 mol yr-1 of NH4+, NOx, TN, P and OC, respectively, to the coastal zone. The nutrient export patterns suggest that N and P loading to rivers in the Altamaha River watershed was greatest in the upper watershed where high population densities were found, and in-stream processing, dilution, and only moderate inputs during transit through the lower watershed resulted in relatively low export from the watershed to coastal waters.

Weston, N.B., Porubsky, W.P., Samarkin, V., MacAvoy, S.E., Erickson, M. and Joye, S.B. 2006. Porewater stoichiometry of terminal metabolic products, sulfate, and dissolved organic carbon and nitrogen in estuarine intertidal creek-bank sediments. Biogeochemistry. 77:375-408.

Abstract
Porewater equilibration samplers were used to obtain porewater inventories of inorganic nutrients (NH4 +, NOx, PO4 3-), dissolved organic carbon (DOC) and nitrogen (DON), sulfate (SO4 2-), dissolved inorganic carbon (DIC), hydrogen sulfide (H2S), chloride (Cl-), methane (CH4) and reduced iron (Fe2+) in intertidal creek-bank sediments at eight sites in three estuarine systems over a range of salinities and seasons. Sulfate reduction (SR) rates and sediment particulate organic carbon (POC) and nitrogen (PON) were also determined at several of the sites. Four sites in the Okatee River estuary in South Carolina, two sites on Sapelo Island, Georgia and one site in White Oak Creek, Georgia appeared to be relatively pristine. The eighth site in Umbrella Creek, Georgia was directly adjacent to a small residential development employing septic systems to handle household waste. The large data set (>700 porewater profiles) offers an opportunity to assess system-scale patterns of porewater biogeochemical dynamics with an emphasis on DOC and DON distributions. SO4 2- depletion (SO4 2-)Dep was used as a proxy for SR, and (SO4 2-)Dep patterns agreed with measured (35S) patterns of SR. There were significant system-scale correlations between the inorganic products of terminal metabolism (DIC, NH4 + and PO4 3-) and (SO4 2-)Dep, and SR appeared to be the dominant terminal carbon oxidation pathway in these sediments. Porewater inventories of DIC and (SO4 2-)Dep indicate a 2:1 stoichiometry across sites, and the C:N ratio of the organic matter undergoing mineralization was between 7.5 and 10. The data suggest that septic-derived dissolved organic matter with a C:N ratio below 6 fueled microbial metabolism and SR at a site with development in the upland. Seasonality was observed in the porewater inventories, but temperature alone did not adequately describe the patterns of (SO4 2-)Dep, terminal metabolic products (DIC, NH4 +, PO4 3-), DOC and DON, and SR observed in this study. It appears that production and consumption of labile DOC are tightly coupled in these sediments, and that bulk DOC is likely a recalcitrant pool. Preferential hydrolysis of PON relative to POC when overall organic matter mineralization rates were high appears to drive the observed patterns in POC:PON, DOC:DON and DIC:DIN ratios. These data, along with the weak seasonal patterns of SR and organic and inorganic porewater inventories, suggest that the rate of hydrolysis limits organic matter mineralization in these intertidal creek-bank sediments.

Whitby, H., Hollibaugh, J.T. and van den Berg, C.M. 2017. Chemical speciation of copper in a salt marsh estuary and bioavailability to Thaumarchaeota. Special Issue: Organic ligands - A key control on trace metal biogeochemistry in the ocean. Frontiers in Marine Sciences. 4. (DOI: 10.3389/fmars.2017.00178)

Abstract
The concentrations of dissolved copper (Cud), copper-binding ligands, thiourea-type thiols, and humic substances (HSCu) were measured in estuarine waters adjacent to Sapelo Island, Georgia, USA, on a monthly basis from April to December 2014. Here we present the seasonal cycle of copper speciation within the estuary and compare it to the development of an annually occurring bloom of Ammonia Oxidizing Archaea (AOA), which require copper for many enzymes. Two types of complexing ligands (L1 and L2) were found to dominate with mean complex stabilities (log K′CuL) of 14.5 and 12.8. Strong complexation resulted in lowering the concentration of free cupric ion (Cu2+) to femtomolar (fM) levels throughout the study and to sub-fM levels during the summer months. A Thaumarchaeota bloom during this period suggests that this organism manages to grow at very low Cu2+ concentrations. Correlation of the concentration of the L1 ligand class with a thiourea-type thiol and the L2 ligand class with HSCu provide an interesting dimension to the identity of the ligand classes. Due to the stronger complex stability, 82–99% of the copper was bound to L1. Thiourea-type thiols typically form Cu(I) species, which would suggest that up to ~90% copper could be present as Cu(I) in this region. In view of the very low concentration of free copper (pCu > 15 at the onset and during the bloom) and a reputedly high requirement for copper, it is likely that the Thaumarchaeota are able to access thiol-bound copper directly.

White, S.N. and Alber, M. 2009. Drought-associated shifts in Spartina alterniflora and S. cynosuroides in the Altamaha River estuary. Wetlands. 29(1):215-224. (DOI: 10.1672/08-39.1)

Abstract
In estuarine systems, informed water resource management decisions rely, in part, on bow in freshwater inflow and salinity affect a selected management target habitat changes). This examined the distribution of altemiflora and S. cynosuriodes the Altamaha River estuary in in association with an extensive during which time freshwater inflow decreased and salty water encroached into previollsly brackish areas. Bankside was of the estuary at the and end of the drought (2000. and again in 2004 after flows had increased. In addition, a removal which one or the other plant was removed from naturally mixed communities, was conducted drought (2001-2002). In all surveys, S. cynosuroides densities decreased at a location that to where average high tide salinities were> 14 psu, such that the downstream border shifted from approximately 3 to 6 km from the mouth of the river between 2000 and 2002 and then back to 3 km in 2004. Although the of S. altemiflora also shifted upstream between 2000 and 2002, upstream densities were in 2004 and distribution did not with In the removal densities and relative % cover of S. increased in all treatments remained constant except in treatments where it was removed. These results suggest that S. is a strong invader that can into new habitat under stressful salinity, low flow) conditions, and that once it is established it can co-exist with S. The more response of S. cynosuroides (shifts occurred within 2 suggests that its downstream limit is a indicator of in inflow conditions in this system.

Widney, S., Smith, D., Herbert, E., Schubauer-Berigan, J.P., Li, F., Pennings, S.C. and Craft, C.B. 2019. Chronic but not acute saltwater intrusion leads to large release of inorganic N in a tidal freshwater marsh. Science of the Total Environment. 695. (DOI: https://doi.org/10.1016/j.scitotenv.2019.133779)

Abstract
Sea level rise is expected to increase inundation and saltwater intrusion into many tidal freshwater marshes and forests. Saltwater intrusion may be long-term, as with rising seas, or episodic, as with low river flow or storm surge. We applied continuous (press) and episodic (pulse) treatments of dilute seawater to replicate 2.5 × 2.5 m field plots for three years and measured soil attributes, including soil porewater, oxidation-reduction potential, soil carbon (C), and nitrogen (N) to investigate the effects of continuous and episodic saltwater intrusion and increased inundation on tidal freshwater marsh elemental cycling and soil processes. Continuous additions of dilute seawater resulted in increased porewater chloride, sulfate, sulfide, ammonium, and nitrate concentrations. Plots that received press additions also had lower soil oxidation-reduction potentials beginning in the second year. Episodic additions of dilute seawater during typical low flow conditions (Sept.-Oct.) resulted in transient increases in porewater chloride and sulfate that returned to baseline conditions once dosing ceased. Freshwater additions did not affect porewater inorganic N or soil C or N. Persistent saltwater intrusion in freshwater marshes alters the N cycle by releasing ammonium-N from sorption sites, increasing nitrification and severely reducing N storage in macrophyte biomass. Chronic saltwater intrusion, as is expected with rising seas, is likely to shift tidal freshwater marshes from a sink to a source of N whereas intermittent intrusion from drought may have no long term effect on N cycling.

Wieski, K. and Pennings, S.C. 2014. Climate Drivers of Spartina alterniflora Saltmarsh Production in Georgia, USA. Ecosystems. 17(3):473-484. (DOI: 10.1007/s10021-013-9732-6)

Abstract
Tidal wetlands are threatened by global changes related not only to sea level rise but also to altered weather patterns. To predict consequences of these changes on coastal communities, it is necessary to understand how temporally varying abiotic conditions drive wetland production. In 2000–2011, we conducted annual surveys of Spartina alterniflora biomass in tidal marshes at nine sites in and around the Altamaha river estuary on the coast of Georgia, USA. End of the year live biomass was assessed in the creek bank and midmarsh zones to estimate annual net primary production (ANPP). River discharge was the most important driver of S. alterniflora ANPP, especially in creek bank vegetation. Increased river discharge reduces water column salinity, and this was most likely the proximate driver of increased production. In the midmarsh zone, the patterns were less distinct, although river discharge was again the best predictor, but maximum temperature had similar predictive ability. In contrast to results from terrestrial grasslands, we found no consistent evidence for a sharply delimited critical period for any climate driver in the tidal marsh,which indicates that plant growth was responsive to abiotic drivers at any time during the growing season. Results were broadly consistent across multiple sites within a geographic region. Our results differ from previous analyses of production in S. alterniflora marshes, which either identified oceanic drivers of S. alterniflora production or were unable to identify any drivers, likely because the low-latitude sites we studied were hotter and more affected by river discharge than those in previous studies.

Wieski, K. and Pennings, S.C. 2014. Latitudinal variation in resistance and tolerance to herbivory of a salt marsh shrub. Ecography. 37:763-769. (DOI: 10.1111/ecog.00498)

Abstract
Interactions between plants and herbivores often vary on a geographic scale. Although theory about plant defenses and tolerance is predicated on temporal or spatial variation in herbivore damage, no single study has compared the pattern of herbivory, plant defenses and tolerance to herbivory of a single species across a latitudinal gradient. In 2002–2005 we surveyed replicate salt marshes along the Atlantic coast of the United States from Florida to Maine. At each field site we scored leaves of Iva frutescens for herbivore damage. In laboratory experiments we measured constitutive resistance and induced resistance in I. frutescens from high and low latitude sites along the Atlantic Coast. In another common garden experiment we studied tolerance to herbivory of I. frutescens from various sites. Theory predicts that constitutive resistance should matter more when damage is high, and induced resistance when herbivory is high but variable. In the field, average levels of herbivore damage, and spatial and temporal variation in herbivore damage were all greater at low versus high latitudes, indicating that constitutive as well as induced resistance should be stronger at low latitudes. Consistent with this prediction, constitutive resistance to herbivory was stronger at low latitudes. Induced resistance to herbivores was also stronger at low latitudes: it was deployed faster and lasted longer. Theory also predicts that tolerance to herbivory should be greater where average herbivory damage is greater; however, tolerance to herbivory in Iva did not depend on geographic origin. Our results emphasize the value of considering multiple ways in which plants respond to herbivores when examining geographic variation in plant–herbivore interactions.

Wieski, K., Guo, H., Craft, C.B. and Pennings, S.C. 2010. Ecosystem functions of tidal fresh, brackish and salt marshes on the Georgia coast. Estuaries and Coasts. 33:161-169. (DOI: 10.1007/s12237-009-9230-4)

Abstract
We examined patterns of habitat function (plant species richness), productivity (plant aboveground biomass and total C), and nutrient stocks (N and P in aboveground plant biomass and soil) in tidal marshes of the Satilla, Altamaha, and Ogeechee Estuaries in Georgia, USA. We worked at two sites within each salinity zone (fresh, brackish, and saline) in each estuary, sampling a transect from the creekbank to the marsh platform. In total, 110 plant species were found. Site-scale and plot-scale species richness decreased from fresh to saline sites. Standing crop biomass and total carbon stocks were greatest at brackish sites, followed by freshwater then saline sites. Nitrogen stocks in plants and soil decreased across sites as salinity increased, while phosphorus stocks did not differ between fresh and brackish sites but were lowest at salty sites. These results generally support past speculation about ecosystem change across the estuarine gradient, emphasizing that ecosystem function in tidal wetlands changes sharply across the relatively short horizontal distance of the estuary. Changes in plant distribution patterns driven by global changes such as sea level rise, changing climates, or fresh water withdrawal are likely to have strong impacts on a variety of wetland functions and services.

Wilson, A.M., Evans, T., Moore, W.S., Schutte, C. and Joye, S.B. 2015. What time scales are important for monitoring tidally influenced submarine groundwater discharge? Insights from a salt marsh. Water Resources Research. 51(6). (DOI: 10.1002/2014WR015984)

Abstract
Submarine groundwater discharge (SGD) varies significantly across time scales ranging from hours to years, but studies that allow quantitative comparisons between different time scales are few. Most of these studies have focused on beach settings, where the combined variations in fresh and saline SGD can be difficult to interpret. We calculated variations in saline SGD based on a 1 year record of hydraulic head in a salt marsh, where we could isolate variations in saline, tidally driven SGD. Observed SGD varied by an order of magnitude over the course of the year. Groundwater discharge was proportional to tidal amplitude and varied by at least a factor of 2 between spring and neap tides. Monthly average SGD was inversely proportional to average sea level; it increased by nearly a factor of 2 as sea level declined by ∼50 cm from late summer to late winter. This variation was far larger than that predicted by analytic models, owing to the flat topography and inundation of the marsh platform. The effect of short-term (days) variations in sea level associated with wind events and storms was small in comparison. SGD is probably proportional to tidal amplitude in nearly all coastal settings, including beaches. Seasonal variations in sea level may not affect the volume of SGD as significantly in coastal settings where the slope of the intertidal zone is relatively constant, but such variations have the potential to strongly affect the composition of SGD.

Wilson, A.M., Evans, T., Moore, W.S., Schutte, C., Joye, S.B., Hughes, A.H. and Anderson, J. 2015. Groundwater controls ecological zonation of salt marsh macrophytes. Ecology. 96(3):840-849. (DOI: 10.1890/13-2183.1)

Abstract
Ecological zonation of salt marsh macrophytes is strongly influenced by hydrologic factors, but these factors are poorly understood. We examined groundwater flow patterns through surficial sediments in two salt marshes in the southeastern United States to quantify hydrologic differences between distinct ecological zones. Both sites included tall- or medium-form Spartina alterniflora near the creek bank; short-form Spartina alterniflora in the mid-marsh; salt flats and Salicornia virginica in the high marsh; and Juncus roemarianus in brackish-to-fresh areas adjacent to uplands. Both sites had relatively small, sandy uplands and similar stratigraphy consisting of marsh muds overlying a deeper sand layer. We found significant hydrologic differences between the four ecological zones. In the zones colonized by S. alterniflora, the vertical flow direction oscillated with semi-diurnal tides. Net flow (14-day average) through the tall S. alterniflora zones was downward, whereas the short S. alterniflora zones included significant periods of net upward groundwater flow. An examination of tidal efficiency at these sites suggested that the net flow patterns rather than tidal damping controlled the width of the tall S. alterniflora zone. In contrast to the S. alterniflora zones, hypersaline zones populated by S. virginica were characterized by sustained periods (days) of continuous upward flow of saline water during neap tides. The fresher zone populated by J. roemarianus showed physical flow patterns that were similar to the hypersaline zones, but the upwelling porewaters were fresh rather than saline. These flow patterns were influenced by the hydrogeologic framework of the marshes, particularly differences in hydraulic head between the upland water table and the tidal creeks. We observed increases in hydraulic head of ~40 cm from the creek to the upland in the sand layers below both marshes, which is consistent with previous observations that sandy aquifers below fine-grained marsh soils act as conduits for flow from uplands to tidal creeks. This hydrologic framework supports relatively good drainage near the creek, increased waterlogging in the mid-marsh, and the development of hypersalinity adjacent to the freshwater upland. These hydrologic differences in turn support distinct ecological zones.

Wilson, A.M., Moore, W.S., Joye, S.B., Anderson, J. and Schutte, C. 2011. Storm-driven groundwater flow in a salt marsh. Water Resources Research. 47(2):1-11. (DOI: 10.1029/2010WR009496)

Abstract
Storms can cause significant groundwater flow in coastal settings, but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer. We have little information about the effects of smaller storms on coastal flow and how storm-induced variability affects key tidal wetlands like salt marshes, which may remain saline throughout a storm. Here we show that even the distant passage of a moderate storm can strongly increase groundwater flow and transport in salt marsh ecosystems and adjacent barrier islands. Groundwater monitoring and radium isotope tracer analyses revealed significant influx of saline creek water into the confined aquifer below the marsh platform, driven by storm surge. This pulse of fluids reached depths exceeding 5 m, and surge-enhanced tides propagated through the aquifer to affect flow in the upland >100 m from the creek bank. Groundwater discharge from the marsh varied significantly prior to the storm, doubling during inundating tides compared to a period of noninundating neap tides. Storm surge then caused groundwater discharge to decline ∼50% compared to similar inundating tides. Ra- and nutrient-poor creek water that entered the confined aquifer below the marsh was quickly enriched in nutrients and carbon, even on 12 h tidal cycles, so that nutrient discharge was likely proportional to groundwater discharge. Storm-related flow could also drive significant contaminant discharge from developed coastlines. The enhanced transport and variability observed here likely affected hundreds of kilometers of the coastline impacted by the storm.

Wrona, A.M., Batzer, D., Alber, M. and Sharitz, R.R. 2007. Savannah River, Georgia: Science to support adaptive implementation of environmental flows to a large coastal river, floodplain, and estuary. Water Resources Impact. 9(4):21-24.

Abstract
A look at the Savannah River shows how a flood prone system can be managed to protect homes and cities while sustaining the estuary and other areas dependent on its water flows by being adaptive and responsive.

Xue, L., Cai, W.-J., Sutton, A.J. and Sabine, C. 2016. Sea surface aragonite saturation state variations and control mechanisms at the Gray's Reef time-series site off Georgia, USA (2006–2007). Marine Chemistry. 195:27-40. (DOI: 10.1016/j.marchem.2017.05.009)

Abstract
We report an annual cycle of surface seawater aragonite mineral saturation state (Ωarag) during 2006–2007 at the Gray's Reef time-series site off Georgia, USA, calculated based on three-hourly observations of carbon dioxide partial pressure (pCO2) and salinity-derived total alkalinity. Ωarag varied between 2.30 and 4.39 with low values (< 3.00) mainly during February–April 2007 and high values (> 3.50) during July–October 2006 and July–September 2007 as well as during two biological production spikes (April–June 2007). We first present a qualitative analysis of the drivers of Ωarag variability based on property regressions with surface temperature, salinity and apparent oxygen utilization, and then quantify the contributions of temperature, air-sea exchange, mixing, and biological processes to monthly Ωarag net changes using a simple 1-D mass budget model. Our analyses suggest that river inputs played the most important role in the seasonal variation of surface Ωarag, in contrast to temperature control on pCO2. Nevertheless, the primary processes controlling monthly Ωarag net change varied with time of year. Furthermore, river inputs lowered Ωarag by 0.28 and 0.48 in July–August and September–October 2007 relative to the equivalent periods of 2006. This implies that interannual Ωarag variability at this location may be greater than that due to the influence of increased atmospheric CO2 over the past few decades, making efforts to discern decadal coastal ocean acidification trends particularly challenging. In addition, although sea surface salinity varies substantially in coastal waters, our analysis suggests that similar to the open ocean Ωarag is essentially determined by carbonate ion concentration ([CO32 −]), not calcium ion concentration ([Ca2 +]) or the stoichiometric solubility product (K′sp), both varying substantially with salinity. Finally, we show that the difference between total alkalinity (TA) and dissolved inorganic carbon (DIC) is a better proxy for [CO32 −] and Ωarag compared with the ratio (TA/DIC) and helps to better elucidate processes affecting Ωarag in coastal oceans.

Xue, L., Jiang, J., Li, X., Yan, Z., Zhang, Q., Ge, Z., Tian, B. and Craft, C.B. 2020. Salinity Affects Topsoil Organic Carbon Concentrations Through Regulating Vegetation Structure and Productivity. Journal of Geophysical Research: Biogeosciences. 125(1):14. (DOI: 10.1029/2019JG005217)

Abstract
Estuarine salt marshes have been recognized as one of the most efficient carbon sinks in the biosphere, with considerable potential for climate change mitigation. However, there are still uncertainties about the response of soil carbon stocks to enhanced soil salinization caused by accelerated sea‐level rises and aggravated saltwater intrusion. We therefore conducted both field investigations in the Chongming Dongtan salt marsh of the Yangtze River Estuary, China, and manipulative experiments on marsh soils occupied, respectively, by the invasive Spartina alterniflora, and the native Phragmites australis and Scirpus mariqueter, to identify the effects of elevated soil salinity on top soil organic carbon (SOC) concentration. Our field data showed that SOC concentrations were significantly positively associated with soil salinity concentrations, annual net primary productivity, and marsh surface elevation but showed a significant negative relationship with median grain size. Compared with the two native species, S. alterniflora preferred more saline conditions and had a higher SOC concentration. Although raised flooding salinities (0–35 ppt) did not strongly affect SOC concentrations, elevated soil salinities significantly corresponded with low SOC concentrations and plant biomass in manipulative experiments. These findings indicated that soil salinity, plant species, and soil texture were key factors controlling SOC concentrations in the studied salt marsh. Moreover, soil salinity could affect SOC concentrations through regulating vegetation spatial structure and plant biomass production. The further invasion of the S. alterniflora community will exert a positive influence on SOC concentrations in the Chongming Dongtan salt marsh.

Yuan, Y., Castelao, R. and He, R. 2017. Variability in along-shelf and cross-shelf circulation in the South Atlantic Bight. Continental Shelf Research. 134:52-62. (DOI: https://doi.org/10.1016/j.csr.2017.01.006)

Abstract
Variability in along-shelf and cross-shelf circulation in the South Atlantic Bight (SAB) is investigated using altimetry observations. Satellite-derived along-shelf velocity anomalies are in good agreement with independent near-surface current measurements from moored acoustic Doppler current profilers and surface velocities from high frequency radar at adjacent locations. This is especially true if wind-driven Ekman velocities are added to the geostrophic velocities, suggesting that the influence of Ekman dynamics to surface along-shelf flow in the SAB is unusually large. The decade-long time series reveals substantial seasonal variability in surface velocities, with peak poleward anomalies during late spring and summer and strong equatorward flow during autumn. Convergences and divergences in the along-shelf transport between two cross-sections are compared with three-dimensional numerical model results and used to estimate cross-shelf transport across the 50 m isobath in the SAB. The calculation suggests a pattern of weak offshore flow during spring followed by prolonged and relatively stronger offshore flow during summer and early autumn, while cross-shelf velocity anomalies during winter are weak and slightly onshore. Prolonged offshore flow following the peak in river discharge that generally occurs in spring indicates the potential for the establishment of a conduit for offshore export of riverine material. The long-term time series also reveals several large events of interannual variability, including the 2003 cold event observed in the SAB.

Zengel, S., Weaver, J., Pennings, S.C., Silliman, B.R., Deis, D., Montague, C.L., Zimmerman, A., Rutherford, N. and Nixon, Z. 2017. Five years of Deepwater Horizon oil spill effects on marsh periwinkles Littoraria irrorata. Marine Ecology Progress Series. 576:135-144. (DOI: 10.3354/meps11827)

Abstract
The Deepwater Horizon spill (2010) was the largest marine oil spill in US waters to date and one of the largest worldwide. To examine effects of the oil spill on an important salt marsh species over time, we conducted a meta-analysis on marsh periwinkles Littoraria irrorata using published and unpublished sources spanning more than 5 yr (2010−2015), including newly available Natural Resources Damage Assessment (NRDA) and Gulf of Mexico Research Initiative (GoMRI) data sets. We tested the hypotheses that the spill decreased mean periwinkle density, reduced mean snail shell length, and changed periwinkle size distribution. Averaged across multiplestudies, sites, marsh zones (edge versus interior), and years, our synthesis revealed a negative effect of heavy oiling on periwinkles. Snail densities were reduced by 73% in heavily oiled sites across all study-zone-by-year combinations, including adverse effects for both the oiled marsh edge and oiled marsh interior, with impacts observed over more than 5 yr. Mean periwinkle shell length was somewhat reduced at the oiled marsh edge in a few cases; however, periwinkle size distributions displayed greater relative proportions of smaller adults and sub-adults, and fewer large adults, across all years. Given the spatial and temporal extent of data analyzed, this synthesis provides evidence that the Deepwater Horizon spill suppressed populations of marsh periwinkles in heavily oiled marshes for over 5 yr, and that impacts were ongoing and recovery was incomplete, likely affecting other ecosystem components, including marsh productivity, organic matter and nutrient cycling, marsh−estuarine food webs, and associated predators.

Zhang, C., Mishra, D. and Pennings, S.C. 2019. Mapping salt marsh soil properties using imaging spectroscopy. ISPRS Journal of Photogrammetry and Remote Sensing. 148:221-234.

Abstract
Tidal salt marshes sequester and store blue carbon at both short and long time scales. Marsh soils shape and maintain the ecosystem by supporting complex biogeochemical reactions, deposition of sediment, and accumulation of organic matter. In this study, we examined the potential of imaging spectroscopy techniques to indirectly quantify and map tidal marsh soil properties at a National Estuarine Research Reserve in Georgia, USA. A framework was developed to combine modern digital image processing techniques for marsh soil mapping, including object-based image analysis (OBIA), machine learning modeling, and ensemble analysis. We also evaluated the efficacy of airborne hyperspectral sensors in estimating marsh soil properties compared to spaceborne multispectral sensors, WorldView-2 and QuickBird. The pros and cons of object-based modeling and mapping were assessed and compared with traditional pixel-based mapping methods. The results showed that the designed framework was effective in quantifying and mapping three marsh soil properties using the composite reflectance from salt marsh environment: soil salinity, soil water content, and soil organic matter content. Multispectral sensors were successful in quantifying soil salinity and soil water content but failed to model soil organic matter. The study also demonstrated the value of minimum noise fraction transformation and ensemble analysis techniques for marsh soil mapping. The results suggest that imaging spectroscopy based modeling is a promising tool to quantify and map marsh soil properties at a local scale, and is a potential alternative to traditional soil data acquisition to support carbon cycle research and the conservation and restoration of tidal marshes.

Zhang, G., Leclerc, M.Y., Nahrawi, H.B. and Pahari, R. 2017. The presence of nocturnal LLJ-associated shear-sheltering and its impact on atmospheric turbulence. Journal of Geophysical Research - Atmospheres. (in review)

Abstract
This paper confirms the existence of atmospheric shear sheltering whose validation has confounded researchers in otherwise well designed experimental studies. Low-level jets present in the stable boundary layer are theorized by Hunt and Durbin (1999) to prevent large eddies present above the jet from penetrating downward through the jet layer thus modulating both surface turbulence and transport/turbulence properties. Previous studies in the literature present contrasting results when this theory is applied to the atmosphere. The present paper suggests that a key difference between both studies could well lie in the fact that the Smedman et al. (2004) study took place over the ocean while the Duarte et al. (2012) study was carried out at a homogeneous site on land. Spectral analysis of turbulence over a salt marsh on the Georgia coastin the presence of low-level jets shows a suppression of spectral energy at low frequencies in both velocity components and temperature signals. This suppression mechanism maybe partly attributed to the presence of large upward shear above jet cores at this coastal site, effectively impeding larger eddies aloft to penetrate through the jet cores to move downward to the surface. This recent evidence, when coupled with the recent study by both Duarte et al. (2012) and Smedman et al. (2004), thus suggest that shear-sheltering theory appears to hold true for regions of very large horizontally uniform homogeneity such as seas and oceans rather than over land.

Zhang, Y., Huang, G., Wang, W., Chen, L. and Lin, G. 2012. Interactions between mangroves and exotic Spartina in an anthropogenically disturbed estuary in southern China. Ecology. 93(3):588 - 597. (DOI: 10.1890/11-1302.1)

Abstract
Cordgrass (Spartina alterniflora) was introduced to China in 1979 from the United States for reducing coastal erosion. It grows vigorously in China and has spread over much of the Chinese coast, from Leizhou Peninsula to Liaoning, a range of more than 19 degrees of latitude. On the southern coast of China, S. alterniflora has invaded mangrove‐dominated habitats during the last two decades, but little is known about interactions between native mangroves and invasive S. alterniflora.We studied the distribution and competitive interactions between native mangroves and S. alterniflora in the Zhangjiang Estuary at four tidal sites along a salinity gradient: oligohaline upstream, mesohaline, polyhaline, and euhaline downstream. S. alterniflora occurred at all four sites, and several mangrove species occurred at all but the downstream euhaline site. S. alterniflora has invaded the estuary widely and has spread to the lower tidal margins of mangroves. It has not invaded mangrove areas with a closed canopy but has established in the mangrove zone where the canopy was opened by human disturbance.Ramets of S. alterniflora transplanted into the understory of mangrove stands with closed canopies died within 10 weeks, but 37.5% survived and grew well on open mud flats. S. alterniflora had virtually no competitive effect on mangrove seedlings planted at the upstream oligohaline site. However, S. alterniflora competitively reduced biomass of mangrove seedlings to 33% over a period of 14 weeks at the mesohaline and polyhaline sites where human disturbance has opened the mangrove canopy. In contrast, S. alterniflora marginally facilitated growth and survival of experimental seedlings at the downstream euhaline site.In China, mangroves occur along the coastline south of Whenzhou, but they have been severely disturbed and removed widely, mainly by mariculture activities. Natural vegetation patterns and our experimental results suggest that, without intervention, S. alterniflora could gradually replace these mangroves in mid‐salinity regions of Chinese estuaries.

Zhang, Y., Li, B., Wu, J. and Pennings, S.C. 2020. Contrasting latitudinal clines of nematode diversity in Spartina alterniflora salt marshes between native and introduced ranges. Diversity and Distributions. (DOI: 10.1111/ddi.13054)

Abstract
Aim: Introduced species may display or foster novel latitudinal clines because they are not well adapted to their new habitats. We tested the hypothesis that the latitudinal cline in nematode diversity in salt marshes would differ between the native (United States) and introduced (China) ranges of Spartina alterniflora.Location: East Coasts of the United States (30.32–43.33°N) and China (30.36–39.14°N).Methods: We extracted nematodes from soil samples collected at 32 sites along the United States East Coast and 41 sites along the Chinese coast. We compared latitudinal patterns in nematode diversity and composition between the native and introduced ranges.Results: In the native range of S. alterniflora, nematode richness at lower latitudes was almost twice as high as that at higher latitudes. In contrast, we found no latitudinal pattern in nematode richness or diversity in the introduced range of S. alterniflora. Nematode genus richness at all sites in China was about half that at lower latitudes in the United States. Beta diversity of nematodes increased with geographic distance in the United States, but not China.Main conclusions: Nematode diversity did not show latitudinal clines in salt marshes dominated by introduced S. alterniflora in China. A likely explanation is that the recently introduced populations are still relatively genetically homogenous, whereas in the native range, genetic variation in plant populations across latitude drives different nematode communities. We suggest that future studies of introduced species will gain additional insights by taking an explicitly geographic perspective.

Zheng, L., Chen, C., Alber, M. and Liu, H. 2003. A modeling study of the Satilla River estuary, Georgia. II: Suspended sediment. Estuaries. 26(3):670-679.

Abstract
A three-dimensional (3-D) suspended sediment model was coupled with a 3-D hydrodynamic numerical model and used to examine the spatial and temporal distribution of suspended sediments in the Satilla River estuary of Georgia. The hydrodynamic model was a modified ECOM-si model with inclusion of the flooding-drying cycle over intertidal salt marshes. The suspended sediment model consisted of a simple passive tracer equation with inclusion of sinking, resuspension, and sedimentation processes. The coupled model was driven by tidal forcing at the open boundary over the inner shelf of the South Atlantic Bight and real-time river discharge at the upstream end of the estuary, with a uniform initial distribution of total suspended sediment (TSS). The initial conditions for salinity were specified using observations taken along the estuary. The coupled model provided a reasonable simulation of both the spatial and temporal distributions of observed TSS concentration. Model-predicted TSS concentrations varied over a tidal cycle; they were highest at maximum flood and ebb tidal phases and lowest at slack tides. Model-guided process studies suggest that the spatial distribution of TSS concentration in the Satilla River estuary is controlled by a complex nonlinear physical process associated with the convergence and divergence of residual flow, a non-uniform along-estuary distribution of bottom stress, and the inertial effects of a curved shoreline.

Zhou, J., Gilerson, A., Ioannou, S., Schalles, J.F., Gross, B., Moshary, F. and Ahmed, S. 2008. Retrieving quantum yield of sun-induced chlorophyll fluorescence near surface from hyperspectral in-situ measurement in productive water. Optics Express. 16(22):17468 - 17483. (DOI: dx.doi.org/10.1364/OE.16.017468)

Abstract
Magnitude and quantum yield (η) of sun induced chlorophyll fluorescence are determined in widely varying productive waters with chlorophyll concentrations from 2–200 mg/m3. Fluorescence was estimated using linear fitting of in-situ measured surface reflectance with elastic and inelastic reflectance spectra. Elastic reflectance spectra were obtained from Hydrolight simulations with measured absorption and attenuation spectra as inputs. η is then computed based on a depth integrated fluorescence model and compared with Hydrolight calculation results. Despite the large variability of coastal environments examined the η values are found to vary over a relatively narrow range 0.1%–1% with mean values of 0.33%±0.17%.

Zimmer, M., Pennings, S.C., Buck, T.L. and Carefoot, T.H. 2002. Species-specific patterns of litter processing by terrestrial isopods (Isopoda: Oniscidea) in high intertidal salt marshes and coastal forests. Functional Ecology. 16:596-607.

Abstract
The species-specificity of litter processing by three species of isopods at the interface between salt marsh and coastal forest habitats in the south-eastern United States was examined. To quantify isopod performance, measurements were taken of feeding, digestion and growth of isopods fed on three litter types (Juncus roemerianus, Quercus virginiana and Pinus palustris) and on artificial diets containing one of three classes of model phenolic compounds (simple phenolics and hydrolysable and condensed tannins). To quantify the ecosystem impact of isopods, promotion of microbial respiration, changes in detritus chemistry, and the quantity of litter processed by isopod populations were measured. The results support three hypotheses concerning isopod–litter interactions. (i) Isopod performance on different litter types can be predicted based on chemical litter traits, e.g. phenolic concentrations and C : N ratios. (ii) Fully terrestrial isopods are better adapted to the range of phenolics found in angiosperm litter than are semiterrestrial species inhabiting the supralittoral. (iii) Isopod species differ with respect to their impact on decomposition processes due to species-specific digestive capabilities, different effects on microbial decomposition and different rates of net litter processing. Because isopods are transitional between semiterrestrial and terrestrial habitats, unlike most other salt marsh detritivores, they are likely to play a unique role in decomposition processes and in the flux of materials between salt marsh and terrestrial habitats.

Zimmer, M., Pennings, S.C., Buck, T.L. and Carefoot, T.H. 2004. Salt Marsh Litter and Detritivores: A Closer Look at Redundancy. Estuaries. 27(5):753–769.

Abstract
Most primary production of angiosperms in coastal salt marshes enters the detritivore food web; studies of this link have predominantly focused on one plant species (Spartina alterniflora) and one detritivore species (Littoraria irrorata). In mesocosm experiments, we studied the rates and pattern of decomposition of litter derived from four plant species common in southeastern United States coastal salt marshes and marsh-fringing terrestrial habitats. Crustaceans and gastropods were selected as detritivores feeding on, and affecting degradation of, the litter of two monocotyledons and two dicotyledons. Despite interspecific similarities in consumption, detritivores exhibited species-specific effects on litter chemistry and on the activity of litter-colonizing microbiota. The chemical composition of feces depended upon both the litter type and the detritivores’ species-specific digestive capabilities. Growth rates and survival of detritivores differed among litter species. Different salt marsh detritivores are likely to have different effects on decomposition processes in the salt marsh and cannot be regarded as functionally redundant nor can the litter of different plant species be regarded as redundant as food for marsh detritivores.

LTER
NSF

This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.