The distribution of Pectinaria korenilarvae in the Seine river plume was studied in June 1992 in the course of three inshore–offshore transects. Plume waters were characterized by a higher turbidity and a well-developed phytoplankton biomass. The hydrological structure varied greatly among surveys, principally due to lunar tidal cycle and wind events. Pectinaria korenilarval densities were consistently larger, by at least one order of magnitude, in plume waters than they were in ambient shelf waters. The frontal structure of the plume, acting as a physical boundary, may favour transport along a coastal band which offers rich trophic resources and limits offshore export. Nonetheless, some mixing processes were observed between water masses. Wind events were also able to break up the front and induce a large-scale dispersal of larvae. In frontal zones, larval and phytoplankton aggregation was quite variable and this cannot be explained by a calculated index of potential convergent velocities.