Macrozoobenthos of the Zernov's Phyllophora Field, Northwestern Black Sea: species richness, quantitative representation and long-term variations

Abstract

The Zernov's Phyllophora Field (ZPF) is a water area in the northwestern Black Sea (NWBS) that occupied about 11 000 km 2 in the early 20 th century. Since 2008, a water area of 4025 km 2 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 km 2 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)(1958)(1959)(1960), its crises of the second half of the 20 th century (1979, 1984, 1991) and the modern (post-crisis) stage (2010)(2011)(2012)(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 km 2 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 21 st 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.Ключевые слова: Phyllophora, биомасса, запасы макрозообентоса, макрофауна бентоса, многолетняя динамика, морская особо охраняемая природная территория, численность Nature Conservation Research. Заповедная наука 2018. 3(4): 32-43

Partial Recovery of Macro-Epibenthic Assemblages on the North-West Shelf of the Black Sea

“…Set in this context, the signs of recovery in the northwest shelf of Black Sea, documented in this and other studies (Revkov et al, 2018;Samyshev and Zolotarev, 2018) although far from complete, are all the more remarkable. The recovery of this ecosystem after its earlier ecological collapse appeared, in 2006-2008, to be at a stage characterised by: slow recovery of Phyllophora abundance; a shift in benthic communities toward opportunistic species with short life cycles; and a shift in the baseline conditions relative to the situation prior to eutrophication (Friedrich et al, 2014).…”

“…This suggests that the recovery of Black Sea benthic biota subsequent to the reduction of nutrient load may not have been as rapid, or extensive, as suggested for the pelagic ecosystem (Kideys, 2002;Steckbauer et al, 2011). In contrast, Revkov et al (2018), documented macrozoobenthos distribution and biomass via grab sampling in 2010-2013 (c. 5 years a fter this study) and noted species richness comparable to, or greater than, pre-eutrophication data, although this may in part be attributed to differing treatments of the samples. That study and the present one are not comparable in terms of methods (grabs versus video), taxonomic resolution or scope (macrozoobenthos versus epibenthos including algae); nonetheless they both point toward a recovery trend, while suggesting differing points along that continuum.…”

“…It is therefore critically important that the regional players, including the EU, recognise the progress that has been made, and continue to press for regional-scale agreements in areas such as nutrient inputs and fisheries management (O'Higgins et al, 2014), as well as a commitment to long-term studies (McCrackin et al, 2016). Encouraging progress has been made in the declaration of a marine reserve over a large proportion of Zernov's Phyllopora field (Kostylev et al, 2010;Revkov et al, 2018), and the adoption of contemporary adaptive management approaches (Douvere and Ehler, 2011) by several of the Black Sea member states. However, predicted scenarios for the Black Sea ecosystem suggest significant declines (Akoglu et al, 2014b) if current policy settings are retained.…”

“…The Black Sea suffers from the combined effects of anthropogenic eutrophication, overfishing and climate forcing (Mee et al, 2005;Oguz and Gilbert, 2007). By the early 1990s, as a result of unrestrained nutrient inputs, coupled with overexploitation of fish stocks (Daskalov, 2002), habitat loss though intensive near-bottom trawling (Revkov et al, 2018) and the invasion of exotic species (Shiganova, 1998;Shiganova et al, 2003;Siokou-Frangou et al, 2004), this once highly productive habitat was considered a dead zone (Mee, 2006;Todorova et al, 2019). It was characterised by high levels of anthropogenic nutrients delivered by the Danube, Dniester and Dniepr rivers, periodic massive phytoplankton blooms, and anoxic bottom waters during the growing season with virtually no sign of macroscopic epibenthic life, as described elsewhere (Diaz and Rosenberg, 2008;Samyshev and Zolotarev, 2018).…”

“…However, there remains little information about the status and trends in macro-epibenthic assemblage structure and distributions at time-points through the "post-crisis" stage (Revkov et al, 2018), and their relationship with documented changes in sediment, nutrient and water body characteristics. This paper presents results from research cruises in the boreal summer of 2006 (RV Akademik) and spring of 2008 (RV Poseidon) which examined a wide range of benthic and pelagic parameters in the region, as reported elsewhere (Pakhomova et al, 2008;Minicheva et al, 2013Minicheva et al, , 2018Friedrich et al, 2015a).…”