Studying the carrying capacity of Mont Saint Michel Bay (France): respective role of the main filter-feeders

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The macrobenthic community in the bay of Mont-Saint-Michel (English Channel, France) is mainly dominated by filter-feeders, including cultivated species (oysters and mussels). The decline in farming production, along with the significant spreading of the invasive slipper limpet Crepidula fornicata (150.000 T), have led scientists and stakeholders to question about the trophic balance between cultivated and wild (native or invasive nonnative) filter-feeders. An ecological model of the bay was developed, coupling a 2D hydro-sedimentary model (SiAM) and biological models for primary production and filter feeder filtration. The filter feeder model includes cultivated (mussels Mytilus edulis and oysters Crassostrea gigas and Ostrea edulis), invasive (Crepidula fornicata) and wild native species (Abra alba, Cerastoderma edule, Glycymeris glycymeris, Lanice conchilega, Macoma balthica, Paphia rhomboides, Sabellaria alveolata, Spisula ovalis). The real distribution for each species was taken into account into the computational grid and individual filtration rates were imposed. For cultivated and invasive species, which represented the highest density levels, bio-deposition production was also computed in order to evaluate the role of these bio-deposits in re-stimulating chlorophyll levels. From 2008 to 2010, this model will be used by scientists and decision makers as a tool for exploring several scenarios of farming managements and/or environmental factor evolutions and their impacts on the ecosystem.