Caractérisation et déterminisme du développement d'une population de l'annélide tubicole Lanice conchilega (Pallas, 1766) (Polychète Terebellidae) associé à la conchyliculture en Baie des Veys (Baie de Seine Occidentale)

Since the mid 80's, a tidal population of the polychaete Lanice conchilega has proliferated along the eastern part of the "Baie des Veys" (Western part of the Bay of Seine). Population density 7 000 individuals per square meter. This proliferation affected significantly the local oyster farming industry, by resulting increased sedimentation rates. This work try to improved understanding the phenomenon by analyzing at various temporal and spatial scales the ecosystem and its relationship with the Lanice conchilega population dynamics. Several field works were carried out (i.e. bottom type mapping, topography, hydrology) to analyse the occurrence and development of this population taking into account the overall changes of the "Baie des Veys" ecosystem. Spatial mapping of Lanice conchilega over time was performed in 1995 and 1998 to assess temporal changes : 200 ha have been colonized by a 3 500 t (wet weight) polychaete population biomass. This demonstrated the temporal population stability The spatial and temporal population dynamic monitoring shows significant abundance changes over five years. The lacking of juvenile recruitments between 1993 and 1996 suggested adult individuals transfers from subtidal areas to regular tidal population. This hypothesis is discussed Moreover, the physiological ecology of both main species, the Pacific cupped oyster Crassostrea gigas and Lanice conchilega was assessed. Trophic competition, as well as oxygen cunsumption, is likely to occur. The main conclusions suggest several research approaches in terms of population dynamics as well as physiological ecology. Hydrodynamic processes involved in regulating population at the adults transfers and larval transports should be assessed. Similarly incorporating the Lanice conchilega as a trophic competitor would improved the ecosystem modeling of the "Baie des Veys".