American alligator trophic dynamics Dr. Brian R. Silliman Duke University

135 Duke Marine Lab Rd. Duke University Marine Lab Beaufort North Carolina 28516-9721 USA

brian.silliman@duke.edu https://nicholas.duke.edu/people/faculty/silliman https://orcid.org/0000-0001-6360-650X Georgia Coastal Ecosystems LTER Project

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

gcelter@uga.edu https://gce-lter.marsci.uga.edu/ Dr. Brian R. Silliman Duke University

135 Duke Marine Lab Rd. Duke University Marine Lab Beaufort North Carolina 28516-9721 USA

brian.silliman@duke.edu https://nicholas.duke.edu/people/faculty/silliman https://orcid.org/0000-0001-6360-650X Principal investigator James C. Nifong Kansas State University

Kansas Cooperative Fish and Wildlife Research Unit Division of Biology Kansas State University Manhattan Kansas 66506-3501 USA

jcnifong@ksu.edu https://www.researchgate.net/profile/James_Nifong Graduate research assistant 2026

J. Nifong (MS student, UF) and B. Silliman (UF) are assessing population densities of the American alligator on Sapelo Island. They have found that alligators spend significant time feeding and moving in marine waters and can be abundant in marsh creeks with full strength salt water (Table 3). T-tests (P<0.05) revealed three categories of alligator density: high (Oakdale), low (Factory, Blackbeard to Cabretta, Duplin), and medium (all others). They hypothesize that alligators cope with osmotic stress by moving every week or two into freshwater to drink and rest, and then moving back into marine waters to feed. They have also taken tissue samples from over 80 individuals to assess the level of connectivity between these predator populations and marine food sources. Their initial results show a change in diet with age: adult alligators are at higher trophic levels, as demonstrated by their enriched 15N signal, and their 13C signal indicates increased reliance on marsh-derived material.

Question 2: How do the spatial and temporal patterns of biogeochemical processes, primary production, community dynamics, decomposition, and disturbance vary across the estuarine landscape, and how do they relate to environmental gradients? (more information)

LTER NSF Georgia Sapelo Island GCE American alligator denisty isotopic osmotic stress Overall geographic extent of the research project -81.301987 -81.263124 31.486493 31.371003 2006-01-01 2012-11-01

National Science Foundation grant numbers OCE-0620959

estuary marsh complex Duplin River - Duplin River transect used for GCE quarterly hydrographic monitoring surveys. Nominal profiling stations are defined at various locations along the Duplin River west of Sapelo Island, Georgia. -81.301987 -81.263124 31.486493 31.410854 Dean Creek - Doboy Sound/salt marsh site at the southern end of Sapelo Island near Dean Creek and the Sapelo lighthouse. A few small creeks are present, but a large creek (Dean Creek) is easily accessed. Upland is composed of small hammocks and some constructed causeways, with sand dune complexes east of Dean Creek and extending to the beach. Upper end of the watershed is affected by a culvert at Beach Road and heavy student use of marsh immediately adjacent to culvert. A hydrographic sonde is deployed in Doboy Sound near Commodore Island approximately 1.5km from this site. GCE6 is also the focus of Sapelo Island Microbial Observatory research on microbial diversity and genomics (http://simo.marsci.uga.edu) -81.299522 -81.264378 31.394072 31.371003 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) https://link.springer.com/article/10.1007%2Fs10750-017-3255-7 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) http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12306/abstract 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. 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) https://www.sciencedirect.com/science/article/pii/S0022098113000063 GIS-GCET-1706 - American alligator GPS tracking study from May 2008 to September 2010 on Sapelo Island, Georgia https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=631 Eleven-foot alligator with GPS tracker on back being released into marsh after gut pumping and tagging https://gce-lter.marsci.uga.edu/public/resources/projects/AlligatorGPScollar.png 10 foot alligator being noosed https://gce-lter.marsci.uga.edu/public/resources/projects/Alligator.png Alligator densities across the Sapelo Island Creeks. https://gce-lter.marsci.uga.edu/public/resources/projects/AlligatorDensities.png