Determining the Trophic Structure and Underlying Nutrient Source Dynamics of an Estuarine Predator, Cynoscion nebulosus, in a River Dominated Estuary

Apalachicola Bay, located in the panhandle of northwest Florida, is one of the most productive estuaries in the northern hemisphere. The Bay has an extensive network of seagrass beds, brackish water sub-aquatic vegetation (SAV), oyster reefs, and saltmarshes which are thought to provide food resources and predation refuge for several ecologically and economically important marine species.  While prior studies have investigated the spatial and trophic dynamics of estuarine fish communities in Apalachicola Bay and other estuaries, few have included piscivores that occupy the highest trophic levels in the system.  The overall objective of this research is to investigate the relative importance of alternative habitat types (e.g., marine seagrass, saltmarsh, brackish water SAV, oyster reef, mudflat) to spotted seatrout foraging in Apalachicola Bay.  By combining ¹³C, ¹⁵N and ³⁴S stable isotope analysis and traditional gut content analysis we aim to: (1) determine the role of alternative habitats as ultimate nutrient sources underlying the productivity of spotted seatrout, and (2) investigate how diet, nutritional condition, and trophic level of seatrout varies spatially in relation to habitat type and seasonally in relation to variation in river flow.  Here we present preliminary ¹³C, ¹⁵N and ³⁴S isotopic data from 300 spotted seatrout ranging in size from 99 – 595mm standard length which were collected in Apalachicola Bay from spring 2010 through winter 2011.  This study will mark the first attempt to delineate the sources of primary productivity supporting an apex predator within Apalachicola Bay across spatial, temporal and ontogenetic time scales.  This project will also provide considerable insight on how various nutrient sources and habitat types support the productivity of an important estuarine piscivore that both structures estuarine communities and form the basis of important fisheries in the region.