COMMUNITY STRUCTURE AND ENVIRONMENTAL ANALYSIS OF MACROZOOBENTHOS IN YICHANG-ANQING REACHES OF THE YANGTZE MAINSTEM

To systematically understand the community structure of macrozoobethos in the mid-lower Yangtze mainstem, two field investigations were conducted on 13 sections along Yichang-Anqing reaches in May-June and October-December 2016, respectively. A total of 96 taxa of macrozoobenthos were recorded with the most abundant group of aquatic insects that account for 49.0% of the total. The frequency of occurrence was relatively low (<1%) for most species (58.7%), and species composition were obviously different among reaches. The density of macrozoobenthos was (213±58) ind./m², and the biomass was (0.202±0.066) g/m². Community structure was different between pre-flood and post-flood periods, where obvious decreases in both species number and standing crops were found in the latter. Compared with the pre-damming data, community structure of macrozoobenthos had increased species number and decreased standing crops. Environmental analyses showed that velocity was the key factor affecting the distribution of macrozoobenthos, while substrate and water quality parameters were of little importance. The sharp decline in standing crops of macrozoobenthos was closely related to the increased scouring effects in post-damming period. These results suggest to carry out regulation of flow and sediment, to create slow-flow habitats and to strengthen protection of sand bars with regard to macrozoobenthos conservation in the Yangtze mainstem.