Spatial Patterns of Ichthyoplankton Assemblages Along the Eastern English Channel French Coast during Spring 1995

Two surveys were conducted during April and May 1995 along the French coast of the eastern English Channel. They aimed to describe the influence of environmental features--water advection through the Straits of Dover and the hydrological coastal front--on ichthyoplankton assemblages. Multivariate analysis, using the non-metric multi-dimensional scaling and based on the Bray-Curtis dissimilarity index, was associated with multiple regression to characterize the spatial larval distribution and to relate it to the environmental factors. During the April survey only young larvae were found. They were separated into a coastal larvae assemblage, characterized by high water temperature and fluorescence of chlorophyll a and two offshore assemblages limited to high salinity water. During the May survey, young larvae were mainly located in offshore waters, in the south of the Picarde Bay and in the Straits, where high offshore chlorophyll a fluorescence was found. In contrast old larvae were found along the coast, near estuaries. This pattern shows a spatial segregation of developmental stages of larvae in this area due to adult spawning migration, larval drift and ontogentic migration. Larval distributions can be explained by salinity, temperature and concentration of chlorophyll a, but the spatial evolution of those parameters during spring have also to be taken into account for the comparison of the distributions between both surveys.