Seasonal variations of zooplankton species composition and abundance in the Kerch Strait in 2000-2013
The state of zooplankton community was analyzed based on the monitoring surveys, conducted in the Kerch Strait (Black Sea, Russia) in 2000-2013. Seasonal variations in zooplankton abundance, biomass and composition were considered. The material was collected in the whole water column, at the depth range of 6-20 m. Altogether, 263 samples were processed; 44 plankton species were identified. Presence of indigenous Oithona nana, that became extinct in the 1990s, and O. brevicornis and Acartia tonsa, which have been introduced to the Azov and Black Seas Basin, was observed. It is shown that positive changes characterize both taxonomic composition and abundance parameters of all the zooplankton species studied. Copepods and Cladocerans were dominant in the species composition; depending on the season, their percentage rate ranged from 23 % in winter to 38 % in summer. The highest biodiversity was recorded during the summer season, the lowest was recorded in winter. The highest quantitative rates of zooplankton development were marked during the summer season. The average multi-annual abundance was 39,986 ind./m <sup>3</sup>, the biomass made up4020.9 mg/m <sup>3</sup>. In winter, zooplankton showed low quantitative and qualitative values. The lowest zooplankton development rates over the whole research period were observed in winter. The average multi-annual abundance was 3,273 ind./m <sup>3</sup> with the biomass equalling 27.4 mg/m <sup>3</sup>. Noctiluca scintillans, unsuitable for fish feeding, was reported during the whole period of the study, but its share was significant in zooplankton biomass in spring (12-79 %) and in summer (25-99 %).