Fluctuations of Pelagic Species of the Open Black Sea During 1980–1995 and Possible Teleconnections

Abstract

The drastic changes in the Black Sea ecosystem, i.e. the harsh decline of the Black Sea fishery in 1989 and the dramatic changes in the zooplankton were often related to the outburst of the accidentally introduced ctenophore Mnemiopsis leidyi and to other man made events, such as pollution, eutrophication, regulation of river outflows (irrigation, damming) and overfishing. Beginning with the question as to why such changes in the Black Sea ecosystem occurred specifically at the end of the 1980s, the fluctuation of zooplankton stocks in other regions of the world are reviewed and compared with the changes in the Black Sea ecosystem. It transpires that changes in the zooplankton community and in small pelagic fish stocks in the second half of the 1980’s until the beginning of the 1990s were evident in all seas under consideration. These changes were discussed in connection with changes in the climatic regime. Striking changes were observed in the NAO (North Atlantic Oscillation), SO (Southern Oscillation), ENSO (Southern Oscillation (El Nino Index), and ALPI (Aleutian Low Pressure Index) in the second half of the 1980s resulting in changes of the hydrological and meteorological regime (river run off, salinity, sea- and air temperature, atmospheric pressure, precipitation and strength of westerly winds) in the northern hemisphere. It is concluded (hypothetically), that possibly, changes in the weather regime during the 1980s could have triggered the changes in the phyto- and mesozooplankton communities of the Black Sea, which caused the conditions for the outburst of M. leidyi and the decline of the anchovy stock.