Caspian cyanobacteria of Azerbaijan: a complete checklist with ecological and geographical characteristics

The article presents the results of a taxonomic revision of the species diversity of cyanobacteria in the Azerbaijani sector of the Caspian Sea according to literature and original data. For the period from 1870 to 2019, 98 species from 44 genera of Cyanophyceae were found off the Caspian coast of Azerbaijan. Phormidium Kützing ex Gomont, Chroococcus Nägeli, Lyngbya C. Agardh ex Gomont, Oscillatoria Vaucher ex Gomont, Merismopedia F.J.F.Meyen and Spirulina Turpin ex Gomont lead in species number. 64 species from 32 genera were found in both plankton and benthos. 33 species from 20 genera of cyanobacteria were common for these communities. Off the coast of Azerbaijan, 64.7% of the genera and 48.0% of the species of сyanobacteria known for the Caspian Sea as a whole have been identified, which indicates that the marine cyanoflora of Azerbaijan has been studied quite fully. The analysis of ecological and biogeographic features of the identified species is given. Among the cyanobacteria of the Azerbaijani coast, the inhabitants of fresh waters are the most numerous (39.2%), followed by freshwater/brackish and brackish species (35.1% together), marine species are the third (16.5%). The predominance of freshwater and brackish forms reflects the specificity of the Caspian Sea as a closed water body with a lower salinity in comparison with oceanic waters. By ecotopic confinement, most of the species found are known as benthic (62.9%), the proportion of truly planktonic species is 29.9%. At the same time, film-forming species are widely represented not only in benthic communities (82.8%), but also in the water column, where they account for about half of the identified species (48.5%). This is related to the hydrological features of coastal ecotopes, where the surf-wave impact on the marine littoral contributes to the penetration of bottom filaments into the water column. The geographical spectrum is characterized by the predominance of species with a cosmopolitan (45.4%) and sub-cosmopolitan (30.9%) distribution, which reflects the tense ecological situation in the region.