Dramatic change in the copepod community in Sevastopol Bay (Black Sea) during two decades (1976–1996)

The seasonal and inter-annual fluctuation of species composition and abundance of copepods in Sevastopol Bay (Black Sea) are presented for the years 1976, 1979–80, 1989–90, 1995–96. The copepod community of the Sevastopol Bay shifted to an other state from the beginning of the seventies to 1996. The main change in the species composition occurred in 1989–1996, when the average annual number of copepods decreased approximately by a factor of 17 compared to the period 1976; 1979/80. The two most abundant copepod species,Acartia clausi (small form) andOitbona nana, vanished, whileAcartia clausi (typical form) andPseudocalanus elongatus became the dominating species. The percentage of copepods of total zooplankton decreased from 54% to 21%. As possible reasons for the degradation of the copepod community eutrophication, pollution and the impact of the accidentally introducedMnemiopsis leidyi A. Agassiz, 1865 are discussed.