Determination of food sources for benthic invertebrates in a salt marsh (Aiguillon Bay, France) by carbon and nitrogen stable isotopes: importance of locally produced sources

delta(13)C and delta(15)N were measured in benthic invertebrates and food sources collected in the salt marsh of the Aiguillon Bay, France. The results showed that, although Spartina anglica was dominant, this marine phanerogame did not contribute significantly to the carbon and nitrogen requirements of the invertebrates considered in this study. In fact, Macoma balthica, Scrobicularia plana and Mytilus edulis preferentially fed on a mixture of benthic diatoms and marine phytoplankton, but in different proportions, as was estimated through isotope mixing models. However, this isotopic data set revealed complex trophic relationships for the nematode community and for the crab Carcinus maenas which did not allow accurate isotopic determination of food sources.