Zooplankton in the Ligurian Sea: Part II. Exploration of their physical and biological forcing functions during summer 2000

A survey of the biological and physical oceanography of theLigurian Sea was conducted in the late summer of 2000. Forty-onestations were sampled for nutrients, oxygen, fluorescence andhydrographic information. Acoustic backscatter measurementswere used to estimate abundance of small (<5 mm) zooplanktonbiovolume versus depth and the distribution of northern krill,Meganyctiphanes norvegica. Net-tow and underwater video datawere collected to identify the zooplankton present. These datawere used to analyze the Ligurian Sea ecosystem for physicaland biological linkages that control zooplankton abundance anddistribution. Results are compared with those from a similarstudy conducted in 1999. Hydrographic sampling showed a domeof dense water in the southwestern middle of the basin. Thehighest chlorophyll a (Chl a) concentrations were measured inthis area, while small zooplankton biovolume was evenly distributedthroughout the survey. Integrated values of Chl a and smallzooplankton biovolume in 2000 were greater than in 1999. Meganyctiphanesnorvegica, siphonophores and salps were the dominant componentsof the macrozooplankton population in the upper 200 m. In thesampled depth strata, siphonophore abundance did not changeduring the day, while M. norvegica were only caught at night.Acoustic backscatter data show that higher densities of M. norvegicaoccurred in deeper water and in the western and southwesternareas of the Ligurian Sea.