Spatial distribution of some groups of microzooplankton in relation to oceanographic processes in the vicinity of a submarine canyon in the north-western Mediterranean Sea

The purpose of this study is to analyse the spatial distribution of some groups of microzooplankton, including the more common potential prey of fish larvae (e.g. copepod nauplii and copepodites), in relation to oceanographic mesoscale processes in the vicinity of the Palamos Canyon (Catalan Sea, NW Mediterranean) as identified by a set of oceanographic and plankton data (60 μm mesh) obtained during a cruise in May 1992. The area was dominated by the Liguro-Provencal-Catalan current (slope current) that was influenced by the cold, fresh water discharged from the river Rhone and partial perturbations of its flow induced by the Palamos canyon. Spatial distribution of the plankton was examined by cluster analysis. Two main groups of stations and taxa were defined and named the 'Oceanic group' and 'Neritic group', respectively. The Oceanic group was characterized by high concentrations of copepod nauplii and copepodites associated with slope current waters and its intrusions into the submarine canyon. In addition the presence of a large cyclonic eddy, detected by satellite data, at the eastern margin of the slope current could contribute to the concentration of organisms in this zone. The Neritic group was located on the shelf and slope areas and characterized by taxa of neritic-meroplanktonic habits together with copepod nauplii and copepodites. The latter were in lower abundances than recorded in the Oceanic group. The results suggest the microzooplankton groups analysed show well-defined distribution patterns related to the slope current and its interaction with the heterogeneity of the shelf. These in turn, affect the distribution of fish larvae and other predators.