Phytoplankton of the Northwestern Part of the Black Sea in the Odesa Region under Conditions of a Technogenic Disaster

In 2023, the northwestern part of the Black Sea underwent significant ecological changes due to the destruction of the dam of the Kakhovka Hydroelectric Power Plant. The large volume of fresh water with nutrients and the increase in water temperature were responsible for the intensive development of Cyanobacteria and green algae, water bloom in summer, and red tides due to the intensive development of Dinophyta in autumn. Representatives of Bacillariophyta, Dinophyta, Chlorophyta, and Cyanobacteria prevailed. However, their ratio changed significantly under the influence of stress factors. The average monthly phytoplankton numbers in 2023 ranged from 84 thousand cells/L to 4306 thousand cells/L, its biomass - from 0,073 to 3,778 mg/L, and the Shannon diversity index varied in 2023-2024 from 1.10 to 3.58 bits/ind. indicating structural instability of communities in response to extreme hydrological changes. Despite the increasing level of eutrophication and surges in algal numbers and biomass, bioindicators demonstrate signs of phytoplankton adaptation to new conditions and gradual stabilization of the ecosystem. The obtained results indicate the high sensitivity of phytoplankton to hydrological disturbances and emphasize its importance as an indicator group for monitoring aquatic ecosystems under conditions of the technogenic disaster.