Seasonal variations of Mediterranean interstitial opisthobranch assemblages

Characteristic seasonal cycles have been found for interstitial Opisthobranchs living in various sandy biotopes of different exposure in the Gulf of Marseilles (Mediterranean coast of France). Abnormal progressive degradation of the environment caused by increased human pollution and a striking decrease of regional wind frequency throughout a seven year period changed these cycles. The sensitivity of these interstitial Opisthobranchs to the degradation of their habitat makes them valuable biological indicators which could be used to identify clean sublittoral sandy bottoms which need to be protected.