Trophic subsidies of Crassostrea gigas, Mytilus edulis and Crepidula fornicata in the Bay of Mont Saint Michel (France): A δ13C and δ15N investigation

This study focussed on the determination of the main trophic subsidies for three dominant filter feeding molluscs of the benthic community, namely, Crassostrea gigas (Thunberg), Mytilus edulis (L.) and Crepidula fornicata (L.), cultivated or naturally occurring in the Bay of Mont Michel (France). δ13C and δ15N values revealed that the diet of these filter feeders was primarily based on marine plankton together with a lower contribution of the organic matter derived from salt marsh phanerogames, as estimated through the isotopic mixing equations (Isosource). The microphytobenthos inhabiting the intertidal flat and the salt marshes do not contribute significantly to the diet of cultivated and naturally occurring C. gigas and M. edulis. Hence, in this bay, the major trophic pathways differ from previous results obtained in several coastal systems devoted to shellfish culture. This could result from ecological particularities and/or strong hydrodynamic conditions in the Bay of Mont Michel.