Benthic diatoms of the Black Sea: rare, invasive, extinct species and assessment of taxonomic exclusivity

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Assessment of benthic diatom taxonomic diversity under increasing anthropogenic pressure on the Black Sea shelf is necessary to preserve the genetic fund of Bacillariophyta, especially for rare and relict endangered species, as well as for controlling of invasive ones. Currently, the Black Sea benthic diatom flora includes 1100 species and intraspecific taxa, among which almost 50% are singleton species. Assumed the Black Sea flora consists from relict of the Ponto-Caspian and Karangat flora, native species, freshwater species, introducers from the Mediterranean basin, and a group of aliens acclimating to another environmental condition. 8 new genera and over 280 newly found for the Black Sea diatom flora species were noted. Also species not recorded in the World Ocean during the XX century were discovered. Groups of 33 and 11 significant for preservation species were highlighted which the ranks of high and highest taxonomic exclusivity were assigned, respectively. Species formed a mono-species branch on a hierarchical tree, i.e. belonging to the same genus, family or order, has the highest preservation priority compared to a species included in a poly-species branch and phylogenetically close to many others. Disappearance of species with high taxonomic exclusivity leads to significant changes in the structure of diatom hierarchical tree. Maintenance of intact habitat conditions for species with a high taxonomic exclusivity should be primary measure to preserve the high diversity of the Black Sea’ flora Bacillariophyta.