Ecological Systems and Devices Annotation << Back THE DIMENSIONAL STRUCTURE OF MICROCYSTIS AERUGINOSA AS A CHARACTERISTIC OF ZOOPLANKTON FOOD BASE T.N. Gerasimova, A.P. Sadchikov The development of Microcystis aeruginosa begins in mid-June at high water transparency and a temperature of about 16о C. Before that, Anabaena spiroides was dominating in the plankton. The share of M. aeruginosa biomass increased from 8–10 % of phytoplankton biomass Bph (in July) to 66–72 % (in late August). In early September, at a decrease in water temperature to 15о C, the abundance of M. aeruginosa decreased to as little as 6 % of Bph. In mid-summer, at low biomass, M. aeruginosa consisted of individual cells (up to 70% of its biomass). The edible biomass (individual cells and colonies <50 μm in size) accounted for 87 % of its biomass. Colonies 50–100 μm and >100 μm in size accounted for 10 % and 2 % of biomass M. aeruginosa, respectively. In August, during M. aeruginosa blooming, its biomass increased to 28.6 mg/L. Individual cells and colonies <50 μm accounted for 65–85 % of M .aeruginosa population biomass. Throughout the summer, the edible fraction of M. aeruginosa varied from 45 % to 87 % of its biomass. Small-size rotifers (80–200 μm) dominated in plankton; their abundance in different periods of the season reached 3.5–4.5 thous. spec./L. At the beginning of M. aeruginosa blooming, 8 Cladocera species with very low abundance (not greater than 45 spec/L) were recorded. Their size varied within 0.3–0.7 mm. The size of the juvenile specimens of Daphnia longispina and Simocephalus vetulus was <1 mm. Large-size organisms were not recorded in the plankton. Notwithstanding the high proportion of the edible fraction in M. aeruginosa biomass, Cladocera were very few because of the trophic press of fish. Keywords: cyanobacteria, dimensional structure of cyanobacteria, Microcystis aeruginosa, plankton-eating fish, zooplankton, Rotatoria, Cladocera, trophic press of fish onto zooplankton. DOI: 10.25791/esip.8.2023.1393 Pp. 51-57.