Infestation des coquilles d'huîtres Crassostrea gigas par les polydores en Basse-Normandie: recommandations et mise au point d'un traitement pour réduire cette nuisance.

Polydorid species form a complex of 157 Spionidae. Among them, Boccardia polybranchia, Boccardia semibranchita, Polydora ciliata and Polydora hoplura regularly colonize oysters cultivated in Normandy. Only one tenth of the populations survives more than one year. Recruits observed on the East coast of Cotentin come from the rocky calcareous flatness of Calvados. Their reproduction is spread out over all the year but winter recruitment is more prejudicial for oysters. Deepest area are more infested. Polydorids create mudblisters which cause a bad marketing of the oyster production. In order to reduce this harmful effect, it is possible to shift the setting of the oyster towards the end of March, to transfer oysters towards other areas during the peak of recruitment or six months before the marketing. It is also possible to treat oysters with a solution saturated out of salt. Quality of shells treated is clearly improved without inducing loss of growth or surmortality.