Zooplankton in the Ligurian Sea: Part I. Characterization of their dispersion, relative abundance and environment during summer 1999

The distributions of temperature, salinity, chlorophyll and zooplankton were measured in the Ligurian Sea, north of Corsica, in August 1999. To characterize the physical environment, hydrographic and fluorometric profiles were collected. A net and two acoustic systems were used to measure the distribution of small (5 mm) zooplankton. Highest chlorophyll values were strongly associated with a dome of dense water in the center of the Ligurian Basin. Small zooplankton (copepods and smaller), in contrast, appeared to be associated with the periphery of the basin and were negatively correlated with chlorophyll. Large zooplankton were not correlated with either chlorophyll or small zooplankton. Large zooplankton migrated vertically hundreds of meters every night, while small zooplankton did not appear to migrate much. The physical observations were consistent with (i) a well-documented geostrophically driven cyclonic coastal current (the Ligurian Current) fed by sources in the Algerian Basin and Tyrrhenian Sea and (ii) upwelling in the central Ligurian Basin. Large zooplankton, being strong vertical migrators, were potentially insulated from the effects of the currents and therefore stayed resident.