Trophic linkages of primary producers and consumers in fringing mangroves of tropical lagoons

Stable carbon and nitrogen isotope ratios were analyzed to investigate the trophic linkages between primary producers and consumers in fringing mangrove ecosystems of The Bahamas and Biscayne Bay, Florida. The isotope ratios, in conjunction with stomach content analysis, were used to trace the flow of organic matter from the primary organic sources (mangroves, seagrass and macro-algae) to primary consumers and ultimately to the gray snapper (Lutjanus griseus). We found the mean delta^13C value of the primary consumers (-17.1%) to be closely related to the mean values of the macro-algal material (-16.7%) and the seagrass (-10.5%) with very little correlation to the carbon signature of mangroves (mean = -27.4%). Our results suggest the ultimate source of carbon for the primary and secondary consumers, located at our study sites, is algal and seagrass material, individually or possibly as a mixture, and that mangroves are not the sole source of carbon in these systems.