Regional changes in mesozooplankton assemblages in Northeastern Mediterranean, Turkish Straits System and the Black Sea

The aim of this study was to determine regional variations in epipelagic mesozooplankton assemblages at basins with different ecological characters composed of the Black Sea, the Turkish Straits System and the northeastern Mediterranean that encircle continental Turkey at three sides. To achieve this goal, mesozooplankton samplings have been carried out at total 56 stations basinwide during cruises held in March-April and September-October, 2008 within the scope of the Project "Southern European Seas: Assessing and Modelling Ecosystem Changes", EU Contract no. 036949 (SESAME). Samples were collected from different layers based on their unique chemical and physical properties within the epipelagic water column with the use of a WP-2 type zooplankton net of 200-µm mesh size equipped with a closing mechanism. Mesozooplankton abundance and biomass have displayed differences both between and within basins regionally and vertically. Spring mean abundance and biomass values retained at each basin have exceeded those of autumn. To the lowest mean mesozooplankton abundance and biomass were met in northeastern Mediterranean, while to the highest mean mesozooplankton abundance and biomass was reached in the Straits system and the Black Sea, respectively. A total of 159 Copepoda, 11 Chaetognatha, and 6 Cladocera species were defined throughout the study among which 13 Copepoda, 4 Cladocera, and 1 Chaetognatha species were common to all basins. In addition to distinct community structures of all basins; inter basin differences both at horizontal and vertical scales have also been observed. Multivariate analyses applied to species matrices have discriminated dominant species as well as statistically significant ambient parameters (temperature, salinity, density, dissolved oxygen) that helped shape the communities. Surface zooplankton abundance and biomass values have been observed maximal in areas of high primary productivity. Overall, it is concluded that basin specific ambient factors have displayed significant role in creating differences between and among the basins. Key words: Mesozooplankton, northeastern Mediterranean, Black Sea, Turkish Strait Systems