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 amphipods Orchestia gammarellus and Corophium volutator, the polychaete Hediste diversicalor and the pulmonate Ovatella bidentata were analysed using isotopic analysis, together with direct description of gut contents for 0. gammarellus. Analysis of carbon and nitrogen isotopic compositions, as well as of gut analyses, showed that the diet of 0. gammarellus consisted 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 for 0. bidentata and C. volutator, and were otherwise sometimes associated with plant detritus for H. 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. (C) 1997 Academic Press Limited.