OSTRACODS IN THE PLANKTON OF THE SIVASH BAY (THE SEA OF AZOV) DURING ITS TRANSFORMATION FROM BRACKISH TO HYPERSALINE STATE

Abstract

Bay Sivash (the Sea of Azov), the largest lagoon in Europe, demonstrates a sharp ecosystem change due to anthropogenic impact. A pronounced salinity increase occurs as a result of the decision to stop supplying Dnieper water into the North-Crimean Canal. Salinity has increased from 20–22 g/L to 55–75 g/L in the lagoon. This led to the changes of biotic composition. The authors used data on ostracod species composition and abundance in samples of 2014–2016 samples with comparison with data from samples collected in 2004, before the salinity increase. The identification of ostracod species in the Sivash Bay was first made; five species was found in 2004–2016: Cyprideis torosa (Jones, 1850), Loxoconcha bulgarica Caraion, 1960, Loxoconcha aestuarii Marinov, 1963, Cytherois cepa Klie, 1937, Leptocythere devexa Schornikov, 1966. In June and August 2004, the average ostracod abundance in plankton was 22 ind./m3 (CV = 1.506). In October 2014, the ostracod abundance in the plankton reached 210 ind./m3, and in August 2015 – average of 1273 ind./m3 (CV = 1.220). In some plankton samples, ostracods dominated in numbers and reached 3850 ind./m3. In the salinity range of 50–80 g/L, a significant positive correlation was observed between total ostracod abundance in plankton and salinity.