Polychaetes in benthos of Karkinit Bay, northwestern Black Sea
A total of 75 polychaete species (Polychaeta) were recorded as a result of the macrozoobenthos surveys carried out in 2007-2018 in Karkinit Bay, northwestern Black Sea. The previously known taxonomic list of polychaetes was extended by adding 46 new species. To date, 86 polychaete species belonging to 32 families have been identified in Karkinit Bay throughout the period of zoobenthos studies (1930-2018). In terms of number of species, the most widely represented families were the Phyllodocidae (10 species), Syllidae (11), Spionidae (8), and Nereididae (7). During our study, the average population density of polychaetes ranged within 498-1420 ind.·m-2, with a maximum of 17708 ind.·m-2. Differences in the structure and abundance of polychaetes were found between the shallow-water eastern (Zabakalsky) part and the deeper western part of Karkinit Bay. The polychaete taxocene of the shallow waters in the Zabakalsky part was significantly affected by the increase in water salinity due to the damming of the North Crimean Canal in 2014. In 2007-2013, Hediste diversicolor dominated in abundance at stations with a salinity lower than 10 ‰, reaching 2313 ind.·m-2. The population density of H. diversicolor showed an inverse relationship with water salinity. A change of dominant species occurred in the Zabakalsky part in 2016-2018, and the average density of polychaetes decreased 2.7-fold. No significant changes were observed in the western, deep-water part of Karkinit Bay after the closure of the canal. The maximum density values (up to 16740 ind. m-2) were recorded for Melinna palmata in 2007-2013 and for Prionospio cf. cirrifera (up to 2984 ind.·m-2) in 2016-2018. The species Heteromastus filiformis was categorized as leading all over the Bay area.