MORPHOFUNCTIONAL GROUPS OF PHYTOPLANKTON OF THE KAZAN BAY
The article presents data on the composition of dominant species of phytoplankton in the Kazan Bay in 2017. The morphofunctional classification of freshwater phytoplankton shows the seasonal succession of the main algal flora associations. The isolation of morphofunctional groups of phytoplankton of the Kazan Bay was investigated for the first time in our work. During the period of the studies on the average relative abundance, Chrysophyta in April, Bacillariophyta from April to June, Cyanophyta from July to October prevailed; biomass was the highest from April to June and in October for diatoms, from July to September for blue-green algae. The heyday of Cryptophyta was recorded in July, for Dinophyta in August. According to the functional classification (FG) of freshwater phytoplankton and the largest average relative abundance and biomass of dominant species ( Planktothrix agardhii, Aphanizomenon flos-aquae, Stephanodiscus huntzschii, St. minutulus, Synedra ulna, Chromulina tenera, Chr. rosanoffii, Cryptomonas erosa, Cr. ovata, Ceratium hirundinella ), the community of the phytoplankton of the Kazan Bay can be classified as B, D, S1, H1, X3 (quantity) or D, S1, L<sub>O</sub>, Y (biomass). Group B represents species of mesotrophic waters, which prefer shallow water zones sensitive to changes in silicon content in water and to seasonal stratification. Group D - species, mainly found in shallow water areas, resistant to low-light conditions (live in muddy water bodies), to agitation. Group S1 - tolerant to light deficiency (mainly turbid waters) species, which prefer shallow-water eutrophic and highly eutrophic water bodies. Group H1 - tolerant to low nitrogen content eutrophic species, resistant to mixing, prefer shallow water. X3 - oligotrophic species; Y - species characterized by a wide range of habitats, where the ejection press is low, prefer shallow-water eutrophic and highly eutrophic water bodies with low transparency; L<sub>O</sub> - species that prefer shallow-water eutrophic and highly eutrophic water bodies. According to the morphological classification (MBFG) of freshwater phytoplankton and the largest average relative abundance and biomass of the dominant species of phytoplankton in size, they represented by groups II, III and VI ( Chr. tenera, Chr. rosanoffii, P. agardhii, Aph. flos-aquae, St. huntzschii, St. minutulus ), biomass III, V and VI ( St. huntzschii, Cr. erosa, Cr. ovata, P. agardhii, Cer, hirundinella, S. ulna ). Group II represented by organisms of small size (Chrysophyta); III - filamentous forms (Cyanophyta), resistant to low-light conditions, high levels of trophism; V - unicellular flagellate forms of medium and large sizes (Euglenophyta, Cryptophyta, Dinophyta), resistant to reduced nutrient content, to light deficiency; VI - organisms with siliceous exoskeletons (Bacillariophyta), which prefer low temperatures, tolerant to a wide range of trophic status of the reservoir. Seasonal change of dominant complexes was determined by diatom algae. In spring (April, May), diatoms accounted for more than 55 % of the average total abundance and more than 65 % of the biomass of phytoplankton, Chrysophyta developed. According to the morphofunctional classification (FG and MBFG), the complexes belonged to groups B, D, X3 and II, VI. In summer (June, July, August), the relative contribution of diatoms to the total abundance and biomass of phytoplankton decreased, due to the active development of Cyanophyta, Cryptophyta and Dinophyta. A complex of species related to FG D, S1, H1, Y, Lo and MBFG III, V, VI developed in the water. In autumn (September, October), with the water temperature lowering, the average organic matter content rose down to 13.8 (mgO<sub>2</sub>/l), the abundance and biomass of the species FG Y, Lo, H1 and MBFG V decreased significantly, diatoms from FG D and MBFG VI were among the dominant species together with blue-green algae FG S1 and MBFG III. The course of seasonal succession of phyt