THE COMMUNITY STRUCTURE OF ZOOBENTHOS IN THE THREE GORGES RESERVIOR: A COMPARISON BEFORE AND AFTER THE IMPOUNDMENT

To understand the community structure of zoobenthos and their responses to hydrological alterations, we conducted a preliminary study at five locations of the Three Gorges Reservoir in August and November of 2012 and April of 2013. The results were: (1) A total of 43 species were identified. The richness of species was the highest in Mudong (29 species), and the lowest in Zigui (12 species). The dominant species were Polypedilum sp., Procladius sp., Nais inflata, Limnodrilus hoffmeisteri and one species of Gammaridae. (2) In terms of spatial distribution, the density of zoobenthos was the highest in Mudong (81802740) ind./m2 and the lowest in Zhongxian (11642) ind./m2. The biomass was also the highest in Mudong (8.663.65) g/m2, and the lowest in Zhongxian (0.170.06) g/m2. (3) As for the seasonal variation, the density of zoobenthos was the highest in autumn (31401450) ind./m2 and the lowest in summer (11537) ind./m2. The biomass showed a different seasonal pattern, which was the highest in spring (3.83 2.11) g/m2 and the lowest in summer (0.650.46) g/m2. (4) Both the density and the biomass declined along with the increase of water depth, and the decline rate was the highest in shallow areas (water depth 20 m). (5) The analysis of ABC curves indicated that the zoobenthic community in Mudong was most disturbed (W=-0.101), followed by Wushan (W=-0.003) and others. (6) There was a trend of decrease in the biomass and the density of zoobenthos after the impoundment of Three Gorges Reservoir. It is likely that the major factors affecting zoobenthos were the slower flow rate, the increase of water depth, the higher fluctuation amplitude of the water level, and the elevated nutrients in the sediment after the impoundment of the Three Gorges Reservoir.