Summer mesozooplankton distribution in coastal waters of central Greece (eastern Mediterranean). I. Hydrology and group composition

Abstract

Zooplankton and hydrography of the upper 200 m was studied in coastal and pelagic waters off central Greece (eastern Mediterranean) during July 1998. The spatial distribution of the main environmental (temperature, salinity, fluorescence) and zooplankton (abundance, dry-weight, dominant groups) features of the area was delimited over an intense grid of 124 stations. The complex topography of the surveyed area comprised an interesting field for the study of pelagic–coastal interaction and its influence on the taxonomic composition of zooplankton.

A typical summer thermal stratification was observed over the entire study area. Marked differences were found in surface-salinity between the eastern (Aegean Sea) and the western (Ionian Sea) part of the study area, which was attributed to the presence of less saline waters originating from the Black Sea. A deep fluorescence maximum was present in both coastal and pelagic stations. Zooplankton abundance and biomass showed an inshore–offshore gradient with coastal areas being significantly richer than pelagic areas. The taxonomic composition of zooplankton varied greatly both along the inshore–offshore gradient and among the different semi-enclosed Gulfs. Copepods were the dominant group in the pelagic waters comprising 67–78% in terms of mean relative abundance. In coastal areas, copepods were less important with cladocerans (especially the species Penilia avirostris) being the dominant group (44–51%). Appendicularians and chaetognaths comprised an important component of the zooplankton community over the entire surveyed area with mean relative abundance ranging from 2·5 to 14% and 0·6 to 5·8%, respectively.