Sulfur, Carbon, and Nitrogen Isotopes Used to Trace Organic Matter Flow in the Salt-Marsh Estuaries of Sapelo Island, Georgia

The stable isotopes of sulfur, nitrogen, and carbon were used to trace organic matter flow in salt marshes and estuarine waters at Sapelo Island, Georgia. Organic matter inputs from terrestrial sources as detrital input either from forests adjacent to the marshes or from rivers were not detectable by their isotopic signatures in estuarine consumers. The results suggest that there are two major sources of organic matter for the fauna of the marshes and estuarine waters of Sapelo Island: Spartina and algae. The long-standing debate about the relative importance of Spartina detritus and algae in supporting marsh and estuarine secondary production appears from this analysis to be a draw; both sources are important and their relative importance is determined by feeding mode, size, location, and trophic position of the marsh and estuarine consumers.