Impacts of environmental factors and shellfish practices on the Mont-St-Michel Bay ecosystem (France). A modelling study involving scientists, stakeholders and users of the bay

Abstract : The macro-benthic communities of Mont-Saint-Michel Bay, located in the Norman-Breton Gulf (English Channel) along the French coast, are mainly dominated by filter-feeders which include cultivated species (oysters and mussels). The decline in shellfish farms production and the significant spreading of the invasive slipper-limpet Crepidula fornicata have conducted scientists and stakeholders to undertake a reflexion on the trophic balance between cultivated and wild (native or invasive non-native) filterfeeders. An ecological model of the bay was developed, coupling a 2D hydro-sedimentary model along with biological models for primary production and filter-feeder growth. The objectives of the project were first to provide indicators to stakeholders on the future evolution of the trophic resource taking in account environmental modifications and human pressure, and establish with them the scenarios to be developed by the model. To accomplish these objectives different focus groups were organised between scientists and stakeholders. Based on these exchanges scenarios on shellfish practices, watershed runoffs and Crepidula fornicata spreading, were investigated through numerical modeling tools. Then results of the models were presented to 6 stakeholders' focus groups and a social scientist has analysed first the interaction between scientists and stakeholders, second the perception of the models by the stakeholders and the ideas of stakeholders concerning the environmental problems face within the Bay.