Caspian Sea 2011

2010

The introduction and accidental invasion of Nereis diversicolor, Abra ovata, Mytilaster lineatus, and Rhithropanopeus harrisii caused a complete change in the benthic community. Some en- demic species disappeared and these exotic species have become dominant. The accidental invasion of Acartia tonsa occured in the 1980s. This species now dominates zoo- plankton in the Central and South Caspian Sea, producing up to 98% of zooplankton biomass. The invasion of Mnemiopsis leidyi ( ML ) in the late 1990s is of great significance. At present, ML is found throughout the Caspian Sea, except in the extreme north and northeast. According to latest data Mnemiopsis leidyi is found in the North Cas- pian where salinity is less than 2% and in fresh waters of the Volga avandelta, where the salinity is too low (CEP 2002c). The most serious impact from the introduction of this species is on the tulka fisheries, primarily due to the competition for food between these two species and the ML eating the planktonic tulka larva. Also, because tulka is a key part of the diet of Caspian seals, a decline in sprat stocks is likely to have a knock-on effect and cause further declines in seal popula- tions (GIWA 2006). Maximum abundance levels of Mnemiopsis were noted in 2002, measuring 1700 specimens per m 3 in the South Caspian Sea (CEP TDA 2007). It was noted that zooplankton diversity and biomass were reduced two to three times. In many cases, instead of the previously registered 10 - 17 species, only one species ( Acartia tonsa ) was found in 2003. Similar changes were observed in the phytoplankton community. A reduction in the phytoplankton community was observed in the vicinity of the southern coast and cannot be ex- plained, while biomass and diversity in the ben- thic community increased twice over during the same period. After two years, the blooms and biomass associated with Mnemiopsis leidyi started to decline. As amounts of Mnemiopsis leidyi fluc- tuate across the Caspian basin, there have been continuing changes among zoo- and phytoplank- ton. The species composition of both communi- ties has become richer while the diversity. Several

species have been seen in healthy numbers, un- observed for several years. This applies particular- ly to Cladocerans and Copepods found in shallow waters along the south shore. It is clear that the invasion of ML has disrupt- ed the whole Caspian Sea ecosystem – however, other earlier invasive species may have also played a role in changing the Sea’s ecology. It is unclear what the long-term impact of ML in the Caspian Sea will be. Habitats The waters of the Caspian Sea and its coasts are distinguished by a diversity of habitats which are of global importance. Species and their habitats are intertwined, one with the other. The condi- tion of habitats is the basis for species survival, but if disrupted, can also cause their extinction. Key factors in the species sustainability are the availability of suitable habitat, their quality and size, and whether they exist over time. A wide spatial variability of habitats and a diversity of environmental conditions result in a high level of taxonomic regional diversity. Deterioration and destruction of habitats result in a loss of di- versity and a reduction in numbers and quality of species populations. These include rare and endemic species (CEP 2002). Such phenomena can clearly be seen in the Caspian Sea region, with many populations of birds and valuable commercial fish decreasing. Coastal habitats. The coastal scenery and habi- tats in the Caspian Sea region are degraded by a number of natural factors such as fluctuations in sea levels, earthquakes and climate change (CEP 2007a). For the whole Caspian Sea coastal zone, the most frequent human impacts are (1) agriculture (2) extraction of fossil fuels and sea- sonal fishing and hunting, and (3) construction, dredging and dumping (CEP 2006), as well as perepromysel living aquatic resources, the crimi- nal trade, regulation of wastewater flowing into rivers. (2) extraction of fossil fuels and seasonal fishing and hunting, and (3) construction, dredg- ing and dumping (CEP 2006), as well as overex-

63