Influence du vieillissement d'une population de crépidules sur l'épifaune associée. Influence sur le recrutement

Crepidula fornicata (slipper Iimpet) is a gastropod mollusc, coming from the North American east coast. Since its accidentaI introduction on french coasts, fifty years ago, C. fomicata invaded several coastal areas of this country and the bay of Saint Brieuc (Brittany -France) is one of the major site affected by the proliferation. Accumulation of dense mats of the slipper limpet contributes to the modification of the bottom structure and affects the substrate's heterogeneity, allowing the settlement of a diversified vagile and sessile epifauna. In this paper, the effects of the C. fornicata population ageing on epifauna assemblages and recruitment are studied. Quantitative and qualitative analysis of epifauna organisms suggests that, the ageing of the C. fornicata population induces a decrease of the pioneer species Pomatoceros triqueter and an increase of the structural complexity of the substrate and therefore favors the development of others sessile species. However, a decrease of species richness of vagile epifauna is observed, probably due to the enhancement of silt and clay sedimentation related to the biological activity of C. fornicata. Results also show that dense colonisation of stacks by epifauna may impede the settlement of slipper limpet new recruits, but alternatively, availability of many substrates (shells) for juvenile settlement seems to offset the problem of spatial competition. Other population regulation factors such as : (i) the weakening effects of the drilling sponge Cliona celata on colonized individuals and (ii) the enhancement of fine particules sedimentation resulting in an increase of filtration and particules sorting activity, which leads to an increase of the energetic demand, seem to contribute to growth alterations.