A preliminary study of the influence of a coastal frontal structure on ichthyoplankton assemblages in the English Channel

Larval fish surveys were made during spring 1993 along the Opale coast (northern France) to describe the hydrological influences on inshore–offshore ichthyoplankton assemblages. The French coast of the north-eastern English Channel is characterised by a coastal water mass, 3 to 5 miles wide, that is separated from offshore water by the presence of an unstable tidal front. Multivariate analysis was used to identify larval fish assemblages. Three kinds of larval distributions were found: (1) offshore larvae, whose distribution was defined by the position of the spawning area, (2) coastal larvae, which were mainly older larvae moving to coastal nursery grounds, and (3) inshore–offshore larvae, depending on the change of spawning areas during the spring. The influence of a tidally-dependent hydrological front was related to inshore–offshore larval exchange and larval development. The changing structure of the frontal zone influenced larval distribution and may be regarded as a regulating factor for the annual recruitment of different species.