Mesozooplankton distribution in relation to hydrology of the Northeastern Aegean Sea, Eastern Mediterranean

The Northeastern Aegean Sea (NEA) is the area where Black Sea waters (BSW) outflow in the Mediterranean enhancing local productivity and inducing high hydrographic complexity. We describe the structure and distribution (both vertical and horizontal) of mesozooplankton assemblages in the NEA during the thermal stratification period in July and September 2003, in an effort to identify BSW effects. The overall standing stocks of mesozooplankton in the NEA were much higher than those typically reported for other pelagic waters of the eastern Mediterranean. Higher abundance and biomass values and a distinctive copepod and cladoceran species assemblage were recorded in the surface layer (directly influenced by the BSW). Variability in the supply and subsequent advection of BSW in the NEA seemed to be the major factor affecting the structure and distribution of mesozooplankton assemblages. In July, lower surface salinity reflected the increased supply of BSW (rich in organic carbon) and, consequently, the abundance of filter feeding taxa (cladocerans, appendicularians and doliolids) was higher than in September. During both surveys, the copepod/cladoceran assemblages of the surface (0–50 m) layer were sensitive tracers of horizontal hydrological and biological variability (e.g. location of fronts) associated with the advection of the BSW.