Species Composition and Toxic Potential of Cyanobacteria in Some Western Rhodopes Dams

Cyanobacteria are photosynthetic prokaryotes with cosmopolitan distribution. They are major producers of primary biomass and free oxygen in most of the freshwater and marine biomes on the planet. Under certain conditions of the environment, these organisms can evolve massively and cause the so-called "water blooms". Very often these blooms are toxic due to the ability of some cyanobacteria to produce dangerous toxins (cyanotoxins) with hepatotoxic, neurotoxic or dermatotoxic effects. This determines the cyanobacteria as an ecological risk for the aquatic ecosystems as well as a threat for the health of animals and humans. Climate changes also lead to an increase in the percentage of cyanobacterial blooms. Therefore, the investigation of the species composition of this group in the Bulgarian reservoirs, the tracking of the blooms frequencies as well as the assessment of their toxic potential is of great importance. Unfortunately, such data at this stage are scarce. This study presents data on the species composition and toxic potential of Cyanobacteria during the summer months of 2017 in five reservoirs (Batak, Dospat, Shiroka polyana, Golyam Beglik and Krichim dams) in the Western Rhodope Mountain. During the investigation period, except the representatives of Cyanobacteria, seven algal phyla (Chlorophyta, Bacillariophyta, Euglenophyta, Dinoflagellata, Cryptophyta, Chrysophyta and Xantophyta) were also found in the dams. The frequency and percentage of cyanobacteria were reported. A taxonomic list of the determined cyanobacterial species is given for each water body. In addition, a quantitative characteristic for each species (density and biomass) was performed. By using ELISA tests for cyanotoxins we have analyzed the presence of microcystins/nodularins (MCs/Nod) and saxitoxins (STXs). Cyanotoxins were found in four of the studied water basins - Dospat Dam, Batak Dam, Shiroka polyana Dam and Krichim Dam.