Stable Isotopes and Gut Analyses to Determine Feeding Relationships in Saltmarsh Macroconsumers

While some saltmarsh vegetation is exported by tides to coastal waters, most saltmarsh vegetation remains and decomposes on site. After microbial action, this plant material can be assimilated by macro-invertebrates. Diets of the amphipodsOrchestia gammarellusandCorophium volutator, the polychaeteHediste diversicolorand the pulmonateOvatella bidentatawere analysed using isotopic analysis, together with direct description of gut contents forO. gammarellus. Analysis of carbon and nitrogen isotopic compositions, as well as of gut analyses, showed that the diet ofO. gammarellusconsisted of more than 50% plant detritus, although its origin was difficult to identify in gut contents. For other species studied, benthic diatoms were the most important food source, sometimes exclusively so forO. bidentataandC. volutator, and were otherwise sometimes associated with plant detritus forH. diversicolor. In this study, isotopic analyses provided a good indication of macro-invertebrate diets. The results confirm those of other studies which indicate that these four invertebrates are deposit feeders.