Régression des herbiers de zostères dans le Bassin d’Arcachon : état des lieux et recherche des causes

While they had previously presented a hight stability, unlike in many coastal sites worldwide, eelgrass beds (Zostera noltii and Zostera marina) of Arcachon Bay have declined sharply since the 2000s. Various causes have been invoked to explain this phenomenon: climate anomalies, disease, over-grazing by herbivorous birds, contamination by herbicides, mechanical destruction during clam fishing. A multidisciplinary study was set up to study the possible effect of these factors, by putting into perspective the history of the seagrass beds and the temporal evolution of these parameters. After a chapter dealing with recent trends (2007-2010) of seagrasses in the Bay of Arcachon, the results relative to the various hypotheses are presented. These results allow to reject some suspected explanatory factors and retain others classifying them according to their relevance. Finally, this work lead to the need for further work, particularly in the field of ecotoxicology, and dealing with the light reaching the seagrasses.