Benthic foraminifera are known to respond quickly to environmental changes. Biological indices are used in marine subtidal areas (Barras et al., 2014) to monitor impacted marine environments (Mojtahid et al., 2006, 2008). Such indices could be useful in transitional marine environments such as estuaries and mudflats where no accurate indices are available. To develop such to ols and to improve our knowledge
on b enthic foraminifera in intertidal environments, we followed the spatial and temporal distribution of b enthic foraminifera in Bourgneuf Bay, a coastal bay with a large mudflat situated south of the Loire estuary on French west coast. At this location, wild oyster reefs are present. Partial release of organic
and inorganic nutrients through oyster excretion enriches the nutrients flow leading to microphytobenthos
bloom around the reef. To show this relation and to understand the relation between the different biological compartments,we analysed the foraminiferal composition of the sediment around the reef before and after ananthrop ogenic manipulation. In July 2014, the oysters of the reef were removed in
order to assess their impact on microphytob enthos and meiofauna. In this study, we showed a strong impact of this anthrop ogenic manipulation on benthic foraminiferal densities and species composition.
These results confirmed the strong and quick responses of benthic foraminifera from intertidal areas to
environmental changes and showed that intertidal benthic foraminifera can be used as an index to monitor transitional marine environments.

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