Date of Award

8-26-2026

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Derek Crane

Second Advisor

Ryan Rezek

Third Advisor

Daniel Abel

Additional Advisors

Matthew Kimball

Abstract

Estuaries are among the world’s most productive ecosystems in the world and are characterized by the convergence of two distinct habitats, creating a mosaic of environmental conditions from inland rivers to the nearshore ocean. Many fishes occupy estuaries during various life stages for growth, reproduction, or foraging, and may reside in them seasonally. The co-occurrence of species, particularly upper-trophic level carnivores, can result in competitive interactions for prey resources within a shared environment. Identifying the degree of these interactions as well as understanding basal energy consumption can inform food web dynamics and how overlapping species use shared spaces. I used bulk stable isotope analysis to investigate trophic ecology of four estuarine predators: sandbar sharks (Carcharhinus plumbeus), bull sharks (Carcharhinus leucas), longnose gar (Lepisosteus osseus), and red drum (Sciaenops ocellatus) in Winyah Bay, South Carolina. Stable carbon, nitrogen, and sulfur isotope signatures from these four predators and primary producers revealed estuarine phytoplankton as a prominent basal resource, with additional contributions from smooth cordgrass (Sporobolus alterniflorus) for sandbar and bull sharks and freshwater phytoplankton for red drum and longnose gar. Despite shared basal resource use, isotopic niche overlap was limited among the species, with sandbar and bull sharks exhibiting the highest, yet moderate, overlap, longnose gar and red drum showing comparatively lower overlap, and minimal overlap observed between sharks and bony fishes. These findings demonstrate how a predator guild can use a widely available basal resource while isotopically partitioning a common environment.

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