Effects of invader Mnemiopsis leidyi on the Caspian Sea ecosystem functioning.
Shiganova, Tamara*,1, Javanshir, Arash2, 1 Shirshov Institute of Oceanology RAS, Moscow, Russia2 University of Tehran, Karaj, Iran
ABSTRACT- During last century Caspian Sea was invaded by a number of alien species, which seriously affected native biodiversity in both pelagic and bottom communities and the whole ecosystem functioning. The most dramatic effect on ecosystem was recorded after invasion of the ctenophore Mnemiopsis leidyi. M. leidyi first was introduced with ballast water from the ships in early 1980s into the Black Sea from the Atlantic coast of North America. IM.leidyi had explosive outbreak in the Black Sea and expanded into the Azov, Marmara, eastern Mediterranean through the straits, and in 1999 into the Caspian Sea with ballast waters of oil tankers. This invasion was a real catastrophe for the Black and Azov Sea ecosystems and fisheries, and now situation is even worse in the Caspian Sea. In 2000 M.leidyi spread across all areas of the Caspian with a salinity not less than 4,3. In 2001 it greatly increased in population size (wet mean biomass 1 kg. m-2 (55 g m-3) in, a abundance two times higher than the highest values in the Black Sea. And in 2002 this biomass doubled. The M.leidyi population study in the five years has revealed that its main area of distribution is the Southern Caspian, where it spends winter and where its population size plummets, as temperatures drop to 8-10 o C, while surviving individuals shrink back to a small size. In spring, it begins to grow and reproduce, spreading to the north.. It appears in the Middle Caspian in July and in the Northern Caspian in late July-early August. Effects on the ecosystem were faster and stronger than in the Black Sea. In 2001, effects were felt at all trophic levels. Functioning ecosystem was changed in the same scheme. On one hand bottom up cascading effect occurred at high trophic levels from decreasing zooplankton stock through planktivorous fish to fish and seal predators, on another hand top-down cascading effect occurred at the lower trophic levels : from decrease zooplankton stock to phytoplankton increase relaxing from herbivorous zooplankton pressure. Thus the Caspian Sea example showed again that this primitive but very well adapted for rapid expansion gelatinous invader , could suppress whole ecosystems and type of their function ×
Key words: invader, ballast waters, ecosystem, the Caspian Sea
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