Zodarsed

The Arcachon Bay is colonized by the largest European Zostera noltei meadows and by Zostera marina with a smaller extent. These seagrasses are known to provide several ecosystem services. However, since 1989 seagrass beds extent dramatically decrease in the Bay. Although a recent study shown that summer heat waves in 2003 and 2006 may be incriminated, the causes of this decline remains not fully understood. Moreover, since the beginning of the decline, an increase of suspended sediment concentration is observed without correlation with wind energy, and is associated with an infilling of eastern shallow channels. Within this context, the main objectives of the present project are (1) to better understand the physical causes of Zostera spp. decline, (2) to unravel physical consequences and quantify possible synergetic effects interplaying between the seagrasses and the sediment dynamics in the bay, and (3) to investigate past and future ecosystem responses to changes of environmental conditions. This will be done combining existing field and laboratory data analysis, new field experiments and, by improving and using the coupled models (hydrodynamics - sediment dynamics - biogeochemistry - seagrass growth) recently developed at Ifremer. The present project also matches priorities 1 and 3 of the COTE LabEx throughout an approach coupling physical processes (Ifremer LER and ODE-DYNECO-PHYSED, and UMR EPOC-METHYS) and, seagrass biology and ecology (Ifremer LER and ODE-DYNECO-PELAGOS, and UMR EPOC-ECOBIOC). The project also deals with the understanding of mechanisms triggering the evolution of an aquatic ecosystem and with the assessment of its medium to long-term response to environmental changes. It would provide a societal answer to recent modifications of the bio-sediment dynamics as well as a valuable tool to further investigate the resilience or the vulnerability of the Arcachon Bay’s seagrass ecosystem.