Dynamique de la population de crépidule (Crepidula fornicata) en Baie du Mont Saint-Michel

A population dynamic study has been carried out on slipper-limpet Crepidula fornicata, in the bay of Mont-Saint-Michel (Brittany, France), for the National Program for Coastal Environment (Programme National d'Environnement Côtier - P.N.E.C.), from samples collected between February and October 2002. Analysis were done on sexuality, reproduction, growth and production. In this population, we observe twice more males than females, which is the consequence of an active reproduction and a sign of a continuous spread. Our results show that the laying period runs from February to October, with two or three main peaks corresponding to a significant rise in water temperature. All females lay eggs in May, but the results demonstrate that the oldest females also lay in autumn, at least for the second time. An in-situ measurement of larval growth rate has been carried out for the first time. In 2002, the first main recruitment period observed began in mid-June. These juveniles start to mature six months later. The maximal calculated length is 54,5 mm after 10 years. This population biomass has a turn-over of around 3 years. It is thus necessary to limit this spread by a continuous harvest. These results have been compared to those obtained four years ago, in the bay of Saint- Brieuc, and showed that these two populations, both situated in the south of the Norman Gulf, are similar.