Structural Variables Of Macrozoobenthos During Stabilization And Increase Of The Small Aral Seas Level (1996-2008)

Abstract

The purpose of this work was to study the macrozoobenthos of the Small Aral Sea in the period from 1996 to 2008, which was characterized by stabilization and then by a steady increase in the water level and decrease in water salinity. Samples of macrozoobenthos were taken in the Small Aral Sea using a grid of 20 stations. During the study period, the average salinity of water varied from 6.3% to 19.0%. 10 taxa were identified in the benthic community. The average annual abundance of macrozoobenthos was 1962 species/m2, with its biomass at 83.3 g/m2. Quantitative variables of the community were primarily formed by polychaete Hediste diversicolor, mollusks Abra ovata, Caspiohydrobia sp. and Cerastoderma isthmicum. During the period of study, abundance and biomass of macrozoobenthos decreased by an order of magnitude from 4274 to 641 species/m2 and from 206.0 to 20.6 g/m2 , respectively. The average values of the Shannon index - 1.20 bits/specimen and 0.92 bits/mg, were characteristic of a low diversity of benthic cenosis. Evidently, the water salinity had a positive effect on the long-term dynamics of macrozoobenthos biomass. The observed decrease in the quantitative variables of macrozoobenthos during desalination of the Small Aral Sea is not only due to the deterioration of hydrochemical conditions for marine and halophilic species, but also to the increased pressure on the benthic fauna caused by fish.