Recruitment of meroplanktonic larvae in the Southern Bight of the North Sea

The density distribution of meroplanktonic larvae is compared with the density distribution of adults in the benthos, at five coastal stations in the Southern Bight of the North Sea (Abra alba community). Plankton communities were sampled during one tidal cycle, along a buoy traject or at a fixed point; southern and northern locations, 250 m from each central sampling point, have been investigated too. Benthos samples were taken only at the central points of this traject. Meroplankton consisted of polychaete larvae (9 families) and bivalve and echinoderm larvae. The highest density values of these larvae (6,400 ind.10.25 m2) are found on the southern sites of each traject (closest to the coastline). The highest meroplankton densities are found where the macrobenthos and meiobenthos density values are low. Results suggest the existence of a larval flux established by specific water bodies running parallel to the coastline. Higher meroplankton densities are present after high water and just before low water. The picture which emerges from this preliminary survey of recruitment shows the important influence of hydrodynamics on biological processes. The meroplankton density distribution pattern at the different locations shows a clear effect of short-term tidally induced variability