Long-term changes in the Black Sea zooplankton: The role of natural and anthropogenic factors

Date

1998-01-01

Author

Kovalev, A
Niermann, U
Melnikov, V
Belokopitov, V
Uysal, Zahit
Kıdeyş, Ahmet Erkan
Unsal, M
Altukhov, D

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Long-term changes in the biomasses of phytoplankton (1959-1985) and mesozooplankton (1957-1996) in relation to natural and anthropogenic factors were reviewed for two different regions of the Black Sea: the shallow northwestern shelf (200 m depth) of the northeastern Black Sea. In the shelf region the influence of climatic factors coupled with high variability in the hydrographic environment and anthropogenic factors, resulted in high fluctuation of the communities. In the eastern deep area the variability seen in the zooplankton was less, and climatic oscillation could be the main factor driving the zooplankton. The phytoplankton showed from the 1960's until beginning of the 1980's an increasing trend, but since then until 1985 their biomass remained at a lower level. The trends in the zooplankton were more variable. During 1958 until mid-sixties first half of the 60'ies the biomass of the mesozooplankton was about 3 times higher at the shelf than in the deep northeastern area. During 1966 the shelf biomass decreased, while the deep water area biomass increased. From the beginning of the 1970's the biomasses of both areas were approximately the same, until the beginning of the 1990's, when the biomasses of in both areas decreased significantly. While at the shelf the biomass was still moderate during 1994, the biomass in the central Black Sea has, recovered since 1992, reaching a maximum in 1995. The strong decrease of the mesozooplankton biomass during the beginning of the 1990's could be related to several factors namely the mass occurrence of the recently introduced ctenophore Mnemiopsis leidyi, to climatic variability indicated by an increased Rossby index, an increase in the Black Sea surface temperature and a decrease in salinity and river discharges during the end of the 1980's, and beginning of the 1990's.

URI

https://hdl.handle.net/11511/116993

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Graduate School of Marine Sciences, Conference / Seminar