Macrozoobenthos of the Zernov's Phyllophora Field, Northwestern Black Sea: species richness, quantitative representation and long-term variations
Authors: Revkov N.K., Boltacheva N.A., Timofeev V.A., Bondarev I.P., Bondarenko L.V.
Number of views: 344
The Zernov's Phyllophora Field (ZPF) is a water area in the northwestern Black Sea (NWBS) that occupied about 11 000 km2 in the early 20th century. Since 2008, a water area of 4025 km2 has been given the status of a botanical sanctuary of national importance «Zernov's Phyllophora Field». The goal of the present study is to assess the species richness and quantitative development of macrozoobenthos of the ZPF and their long-term variations under the current conditions of de-eutrophication of the Black Sea basin. The work is based on the material of 43 benthos stations performed in 2010–2013 within an area of 8400 km2 in the ZPF. In 2010–2013, a total of 162 macrozoobenthos species were identified: Polychaeta (49 species), Mollusca (39), Crustacea (43), Ascidiacea (6); the other taxa comprised 25 species. The current level of species richness of macrozoobenthos is the highest for the entire historical period of the ZPF studies. The mean abundance and wet biomass of macrozoobenthos were estimated at 2417 ± 175 individuals/m² and 283 ± 32 g/m² (without mantle cavity fluid of bivalves). Values for Polychaeta amounted to 1017 individuals/m² and 6 g/m², Mollusca – 887 individuals/m² and 256 g/m², Crustacea – 165 individuals/m² and 1.3 g/m², Ascidiacea – 42 individuals/m² and 17 g/m². The biomass of the dominant species, the filter-feeders Mytilus galloprovincialis, reaches 73% of the total macrozoobrnthos biomass. Our research of the long-term alterations in benthic macrofauna covers the period 1957 to 2013, including the pre-crisis time of the Black Sea ecosystem (1957–1960), its crises of the second half of the 20th century (1979, 1984, 1991) and the modern (post-crisis) stage (2010–2013). Based on the maps of biomass spatial distribution for all periods mentioned above, the mean values and the total stocks of macrozoobenthos within the area 8400 km2 of the ZPF were evaluated. The long-term changes of the macrozoobenthos biomass were analysed in relation to the main factors adversely affected the bottom biocoenoses in NWBS – i.e. anthropogenic eutrophication, oxygen depletion and near-bottom hypoxia in summer, as well as the secondary siltation of the seabed due to intensive near-bottom trawling. The most critical period for the ZPF ecosystem state occurred in the late 1970s, when the mean biomass and the total stock of macrozoobenthos decreased by 7 times in comparison with the pre-crisis period. The data collected in the first decades of the 21st century indicate the actual recovery of the mean macrozoobenthos biomass and of its total stock in the ZPF area to the level of 1957–1960, which is related to the improving of the general ecological situation in the region.