Trophic transfer and habitat use of oyster Crassostrea virginica reefs in southwest Florida, identified by stable isotope analysis

Oyster reefs have been identified as essential fish habitat for resident and transient species. Many organisms found on oyster reefs, including shrimp, crabs, and small fishes, find shelter and food on the reef and in turn provide food for transient species that frequent oyster reefs. The objective of this study was to determine trophic transfer on oyster reefs in a subtropical environment using stable isotope compositions. Water, sediment, particulate organic matter, various crustaceans, fishes, as well as oysters were collected at 2 sites in Estero Bay, Florida, during the wet and dry seasons, and processed for delta C-13 and delta N-15 stable isotope analyses. Differences in freshwater input (salinity) resulted in differences in carbon and nitrogen isotope ratios. Overall, fish and shrimp are secondary consumers, with crabs and oysters as primary consumers, and organic matter sources at the lowest trophic level. Results of the study further demonstrate that reef-resident organisms consume other organisms found on the reef and/or primary producers and detrital organic matter on the reef. Transient fish species come to the reef to feed on the reef-resident species.