Dereziuk N. V.

Purpose. To reveal seasonal changes in phytoplankton quantitative characteristics including biodiversity and species composition of potentially dangerous (toxic) species. Methods. Phytoplankton sampling in Odessa bay coastal waters and sample analyses were carried out using standard methodologies. The samples were preserved using formalin. Microscopes HUND−H600 and OLYMPUS−BH2 have been used for sample analyses. Classification of microalgae and Cyanobacteria was done according to the standards of the international database. Results. Analysis of the main abiotic factors influencing the state of phytocene has been carried out. In the species composition, 238 species of phytoplankton belonging to 11 classes have been registered: diatoms − Bacillariophyceae, dinophytes − Dinophyceae, green − Chlorophyceae, Cyanobacteria, Prymnesiophyceae, Euglenoidea, Chrysophyceae, Cryptophyceae, Dictyochophyceae, Choanoflagellatea. It was shown that the dominant phytoplankton species were Bacillariophyceae, Dinophyceae, Chlorophyceae and Cyanobacteria. For the first time, 11 freshwater species of dinophytes were registered in the Zmiinyi Island area. Statistical interconnections between phytoplankton metrics and abiotic characteristics were analysed. Development of 54 phytoplankton species, which refer to the group of potentially harmful (toxic) was registered; out of this number, 21 reached blooming level. Conclusions. The main abiotic factors determining the state of phytoplankton and its seasonal changes are salinity and transparency. During 2016−2017, 4 seasonal maximums of microalgae development were registered in the photic layer of the Zmiinyi Island coastal waters (in spring, summer, autumn and winter), which corresponded to the terms of the normal periodicity of the Black Sea phytoplankton vegetation. Comparison of modern maximum values with similar data obtained in previous years, allows us to conclude that a significant increase in the quantitative characteristics of phytoplankton took place in 2016−2017. The quality of water in the surface layers in the Zmiinyi Island area assessed using the main metrics of phytoplankton was much lower than that in the bottom water layers, which was caused by the Danube River discharge impact, first of all, observed in the surface layers of water.

The sharp change in the salinity of the Kuyalnitsky estuary in the second half of the twentieth century. Caused a significant reorganization of its ecosystem, which led to loss of fishing, deterioration of the quality of water. At the beginning of the XXI century the study of the Kuyalnitsky estuary biota, which exists in hypergalian conditions, was unsystematic, so information on the quantitative characteristics of phytoplankton and its distribution in the estuary is extremely limited. Purpose. To obtaining detailed information about current composition and quantitative characteristics of phytoplankton species in the estuary during the period from March 2015 to March 2017, i.e. when influenced by the transfer of sea water from the Odessa Bay. Methods. Concentration of the collected samples was done by sedimentation method. The samples collected during microalgal blooms have not been concentrated. Results. The phytoplankton was monodominant all over the estuary in 2015 – 2017 due to development of Dunaliella salina (Dunal) Teodor., which was presented by two different life forms. Some water samples contained benthoplankton species of diatomic algae, as well as Chlorophyta and Cyanobacteria. During the period of study algae blooms of D. salina was registered in 36 water samples; some cases of Bacillariophyta and Chlorophyta blooming were observed as well. During the period 2015-2017 the total number of phytoplankton species in the northern and central part of the estuary reached 23; in the southern part 69 species were registered. Conclusions. It has been established that phytoplankton of Kuyalnik Estuary can quickly adapt to salinity reduction caused by the filling of the estuary with sea water, which is one of the reasons of frequent algal blooms in 2015-2017.