Succession of the ecosystems
of the Aral Sea during its transition from oligohaline to polyhaline water
body
I.M. Mirabdullayev, I.M. Joldasova, Z.A. Mustafaeva,
S. Kazakhbaev, S.A. Lyubimova, B.A. Tashmukhamedov-2004
Journal of Marine Systems, 47: 101-107
Abstract:
During 22 field trips from 1990 to 2002 (mainly the
western basin of the Large Aral) data on salinity, phytoplankton,
zooplankton, zoobenthos and fish fauna have been collected. In 2002, the
salinity of the western basin reached 75 ppt, while that in the eastern
basin, 150 ppt. In 1999–2002, 159 species of planktonic algae have been
recorded. This is approximately twice as low as recorded before. The
diversity of Cyanophyta, Pyrrhophyta and Chlorophyta in particular has
dropped in the past few years. As before, currently Bacillariophyta is the
most diverse plankton. However, the composition of dominants has changed.
Once previously dominant species, Actinocyclus ehrenbergii, vanished
from the plankton of the Aral Sea and was replaced by such diatoms as Amphora
coffeaformis, A. coffeaformis var. acutiuscula and Synedra
tabulata var. parva.
Since 1970s, a gradual decrease in the diversity of
zooplankton has been taking place. Since 1997, the formerly dominant Calanipeda
aquaedulcis vanished, which apparently was the reason for the emergence
of Moina salina and Artemia parthenogenetica. Since 2000, Artemia
has been dominant in the plankton of the Aral Sea, constituting 99% of the
zooplankton biomass.
In the 1970–1980s, a rapid decrease in the
biodiversity of the zoobenthos was observed. In the 1990s, most aboriginal
and introduced species became extinct. Currently, the bivalve mollusk Syndosmya
segmentum, the ostracod Cyprideis torosa and larvae of the
dipteran Chironomus salinarius can still be recorded in the western
basin. In the eastern basin no benthos is observed.
By 1998, in the Large Aral, only five fish species
survived: baltic herring Clupea harengus membras, flounder Platichthys
flesus luscus, atherine Atherina boyeri caspia and bullheads Neogobius
fluviatilis and Potamoschistus caucasicus. Since 2002, only
flounder and atherina have been recorded in the western basin of the Large
Aral. No fish have been recorded in the eastern part of the Aral Sea in
2002.
With increasing salinity and transition of the Aral
Sea from an oligohaline to a polyhaline water body, its biota is becoming
drastically poorer. Almost all local species became extinct in the Aral;
however, some still survive (including some endemics) in some lakes around
the Aral Sea. In the near future, Artemia will be the only animal in
the Aral Sea.
(Institute of Zoology of the Uzbek Academy of
Sciences, Tashkent, 700095, Uzbekistan, e-mail: iskandar@mail.tps.uz)