IMIS

Data were collected in 2003 within the framework of the Ukrainian national monitoring program. Mesozooplankton samples were obtained using a vertical Juday plankton net with a 0.1 m² mouth opening and a mesh size of 150 μm. Vertical hauls were performed from 2 m above the seabed or from the lower boundary of the oxic layer to the surface, depending on local conditions. The sampling depth was determined by accounting for both the length and the angle of the towing wire. Samples were fixed with 4% formaldehyde buffered to pH 8.0–8.2 using disodium tetraborate (borax; Na₂B₄O₇·10H₂O) and stored in plastic containers. Prior to analysis, the material was concentrated to 100–150 cm³ and divided into sub-samples. Quantitative (abundance and biomass based on species-specific individual weights) and qualitative (taxonomic composition) analyses were carried out in a Bogorov chamber under a stereoscopic zoom microscope. At least 100 individuals of each of the three dominant species were counted per sub-sample. According to Alexandrov et al. (2014), the abundance estimates for these groups have an accuracy of approximately 20%. Taxonomic identification followed Morduhay-Boltovskoy (1968, 1969, 1972).