Study of Bioturbation and the Impact on Coastal Erosion of the Biodiversity of Benthic Organisms in the Normandy Territory (Sandy Beaches, Estuaries, Oyster Farms, Harbours)

With over 600 km of coastline, Normandy is highly concerned by the risks of submersion and worries about rising sea levels. These coastal ecosystems are very diverse, and marine biodiversity, particularly that of the benthos, provides numerous ecosystem services, including the morphosedimentary regulation of the seafloor. In particular, benthic organisms are very effective at modifying the physical properties of their habitat in terms of resistance to erosion at local scales. These processes are already well quantified, but often in a mono-specific manner, and studies concerning sediment-biota interactions need to be applied to a greater variety of environments such as oyster farms, estuarine mudflats, and sandy beaches exposed to waves. In situ experiments have been able to prove that the bioturbation of certain populations (Hediste diversicolor, Cerastoderma edule, Mytilus edulis, Magallana gigas) can be responsible for an accumulation of 1 to 2 cm in 15 days (and therefore $\sim$ 50 cm per year). Conversely, other destabilizing species like the bivalve Scrobicularia plana can, on the contrary, decrease the sedimentary level by about 50 cm in a year and can be useful, for example, to prevent the too rapid extension of a salt marsh (or schorre).

The BILBO project proposes to evaluate the complete role of multi-specific communities on different sedimentary facies and along transverse profiles across different types of foreshore to better understand their potential role in sediment accumulation. This project aims to provide a solid foundation for future ecological restoration projects (dike development, de-polderization) or coastal protection (high beaches) in the face of new threats related to rising sea levels (which should reach a rate of 1 to 2 cm per year by 2100 according to the IPCC RCP8.5 scenario).