Changes in the heterogeneity of mesoscale distribution patterns of larval fish associated with a shallow coastal haline front

Abstract

In June 1983 there was a large outflow of inland fresh-waters from the Rhône River that covered a broad area off the northern coast of Catalonia (Northwestern Mediterranean), giving rise to a surface plume of fresh water with a distinct haline front at its southern edge. This hydrodynamic event brought about substantial changes in the structure of the larval fish community in the area, which was in turn reflected in an increase in spatial heterogeneity. Large numbers of species and individuals were found along the southern edge of the plume in association with the haline front, whereas, with the exception of certain species, larval fish concentrations in the area covered by the plume tended to be considerably lower than in the rest of the area. Species predominantly located in the surface water layers were probably transported by the plume out to the plume's edge. Other species, which apparently enjoy a broader vertical distribution range, were less affected by the surface advection processes.