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GCE III - Key Finding in 2016

    The importance of non-trophic interactions in salt marsh communities

    The trophic interactions among salt marsh organisms have been extremely well studied. However, non-trophic interactions such as facilitation may also be important but have received considerably less attention. Research by Angelini et al. (2015) found that aggregations of ribbed mussels (Geukensia demissa) embedded within cordgrass (S. alterniflora) enhanced biodiversity, rates of decomposition, primary production, and water infiltration (Fig. 1). In a companion study focused on salt marsh dieback, Angelini et al. (2016) showed that G. demissa aggregations also enhance water storage and prevent increases in soil salinity during drought. This, in turn, served a protective role for cordgrass, which had a far greater chance of surviving a severe 2011-12 drought and were able to recolonize dieback areas more rapidly if mussel aggregations were present. They also speculated that mussels, by attracting crabs that excavate a burrow network, effectively boost water storage around cordgrass roots. A study of New England marshes has also provided evidence for the importance of facilitation by G. demissa: here, the authors show that mussels facilitate diverse assemblages of intertidal invertebrates and algae, thereby dramatically enhancing food web size and complexity (van der Zee et al. 2016). They extend this insight by evaluating the importance of burrowing activities of swimming crabs in seagrass meadows for promoting large complex food webs in West African intertidal seagrass systems. These studies demonstrate that positive interactions among key species can affect biodiversity, ecosystem functioning and resilience of entire landscapes, and therefore may be important to consider for effective restoration of degraded ecosystems.


    Fig. 1 Links between salt marsh foundation species, invertebrates, and ecosystem functioning. Panels a-f depict the patch-scale effects of mussel aggregations on individual ecosystem functions, average; panel g shows multifunctionality vs patch size; panel h shows the number of functions performed above a series of per cent of maximum functioning thresholds. Panel i is a conceptual model of the direct and indirect effects of cordgrass and mussel foundation species on invertebrate functional groups and ecosystem functioning. The strength of effects is denoted by line weight and direction of effects by line colour (positive, black; negative, grey). Illustration credit: Joseph P. Morton. From Angelini et al. 2015.


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.