IMIS

Data were collected during the Ukrainian national monitoring program in 2004. Mesozooplankton samples were collected using a vertical plankton Juday net with a 0.1 m² mouth opening area and 150 μm mesh size, from 2 meters above the bottom or from the lower boundary of the oxic layer to the surface at discrete sampling layers. The length and angle of the wire were taken into consideration for calculation of the wire length to reach the target horizon. The samples were preserved in 4% formaldehyde buffered to pH 8–8.2 with disodium tetraborate (borax) (Na₂B₄O₇·10H₂O) formalin solution (1 part 40% formaldehyde solution and 9 parts water/sample) and stored in plastic containers. In the laboratory, the samples were concentrated to 100–150 cm³ before being divided into sub-samples. A Bogorov's chamber was used for quantitative assessment (abundance and biomass calculation using species individual weight) and qualitative (taxonomic structure) processing of sub-samples. The sub-samples were examined using a Stereoscopic Zoom Microscope. At least 100 organisms from each of the three dominant species were counted in each sub-sample. The precision of the calculated abundance for organisms of the first three groups, counted up to 100 specimens, amounts to 20% (Alexandrov et al., 2014). Species were identified according to Morduhay-Boltovskoy (1968, 1969 and 1972).