Effects of Cystoseira Sensu lato (Fucales: Phaeophyceae) on Species Richness, Composition, and Biomass of Abrau Peninsula Shelf Macrophytobenthic Communities (Black Sea)

Field observations were applied to study the macrophytobenthos of the Abrau Peninsula of the Black Sea and the effect of the two most common and largest species of brown algae of the Black Sea sublittoral, Cystoseira bosphorica and Treptacantha barbata (Cystoseira sensu lato), on species richness and phytocenosis biomass, as well as biomass and the occurrence of related macroalgae species of different ecological groups. In total, 48 species of macroalgae were found in Cystoseira assemblages, including 27 species of Rhodophyta; 11 species of Ochrophyta, Phaeophyceae; and 10 species of Chlorophyta. It was shown that two- to fourfold decrease in the Cystoseira biomass in communities as a whole does not significantly affect their species richness but leads to a decrease in the total biomass of these cenoses and a multidirectional change in participation (biomass, occurrence) of many species of macroalgae. The response of the cenoses to a decrease in biomass of C. bosphorica and T. barbata, as well as its negative character-a decrease in productivity and species richness-was more pronounced at greater depths.