Suivi des gisements naturels de mollusques dans le cadre du réseau Repamo

A monitoring of the natural and high density populations of commercial molluscs is performed on an annual basis within the scope of the Repamo mollusc pathology monitoring network The aim of this surveillance is (1) to monitor the health status of the molluscs along the French coast and to produce a reference picture, and (2) to study the evolution of the noticeable pathogenic agents existing on the national territory. Different sampling strategies have been introduced for the past 15 years; each strategy is based on an active monitoring including the systematic study of natural mollusc deposits. Indeed, the natural and high density mollusc populations are interrelated and pathogenic agents can be and have been exchanged between these populations with dramatic consequences for shellfish culture. Mollusc farming is performed in the natural milieu, next to natural populations and, very often, natural individuals are collected and kept in farming conditions (spawners, spats); as a matter of fact, the distinction between natural and cultivated populations is really difficult to make especially as farming is mostly performed in an extensive way. These natural populations are also the reflection of a production sector as far as diseases (reservoir, sentinel) are concerned, since mollusc farming is mostly based on transfers. The main natural species studied were the flat oyster Ostrea edulis, the abalone Haliotis tuberculata, the cockle Ceratoderma edule, the clam Ruditapes decussatus and R. philippinarum and the mussel Mytilus edulis and M. galloprovincialis. Different pathogenic agents have been observed and mostly noticeable agents like Bonamia ostreae and Marteilia refringens. The collected data enable the gradual mapping of the French coast regarding the different pathogenic agents. This map could then be used to improve security during transfers, the preservation of pathogen free zones and to better understand a certain amount of abnormal mortality cases