Spatial distribution and community structure of copepods in a central Mediterranean key region (Egadi Islands-Sicily Channel)

During an autumn oceanographic cruise in October 2004, 87 zooplankton samples were collected from 12 sites, located along inshore-offshore sections around the Egadi Island Archipelago, a central Mediterranean key region. Zooplankton samples were taken by the electronic multinet BIONESS, equipped with a multi-parameter probe system in order to measure simultaneously physico-chemical and biological factors (temperature, salinity, dissolved oxygen and fluorescence). Three different water masses were identified from physico-chemical parameter analysis: MAW (0-50 m) widespread all around the study area; a water mass, which is most likely a mixture of western and eastern-origin waters, up to 300 m depth; and LIW in the 300-600 m layer, with a core salinity of 38.72-38.74 at the most offshore stations. Spatial diversity patterns of copepod assemblage were examined using species richness and Shannon-Wiener diversity indices. 107 copepod species were identified. Four major sample groups were identified by cluster analysis, differing in species composition and abundances in relation to the depth and in-offshore environments. They seemed to be only partly related to the different water masses and significantly correlated to temperature and salinity. In the entire study area, the copepod abundances were markedly lower than those reported for other regions of the Mediterranean Sea, but the species richness was relatively high, and similar to the richest Mediterranean areas. This is probably due to geographical position of the Egadi Island Archipelago at the entrance of Sicily Channel, where water mass exchange between Eastern and Western basins occurs.