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

The distributions of temperature, salinity, chlorophyll andzooplankton were measured in the Ligurian Sea, north of Corsica,in August 1999. To characterize the physical environment, hydrographicand fluorometric profiles were collected. A net and two acousticsystems were used to measure the distribution of small (<5mm) and large (>5 mm) zooplankton. Highest chlorophyll valueswere strongly associated with a dome of dense water in the centerof the Ligurian Basin. Small zooplankton (copepods and smaller),in contrast, appeared to be associated with the periphery ofthe basin and were negatively correlated with chlorophyll. Largezooplankton were not correlated with either chlorophyll or smallzooplankton. Large zooplankton migrated vertically hundredsof meters every night, while small zooplankton did not appearto migrate much. The physical observations were consistent with(i) a well-documented geostrophically driven cyclonic coastalcurrent (the Ligurian Current) fed by sources in the AlgerianBasin and Tyrrhenian Sea and (ii) upwelling in the central LigurianBasin. Large zooplankton, being strong vertical migrators, werepotentially insulated from the effects of the currents and thereforestayed resident.