Abstract:
To understand the status quo and variation trend of macrozoobenthos along the mid-lower mainstem of the Yangtze River, three field surveys were carried out from 2019 to 2020. A total of 129 taxa of macrozoobenthos were recorded. The mean density and biomass of macrozoobenthos were 174 ind./m
2 and 0.645 g/m
2 (dry weight, similarly below), respectively. From the middle to the lower reaches, the total taxa number of macrozoobenthos decreased; the density of aquatic insects decreased, while the density of other taxa increased; the density of collector-gatherers and scrapers decreased, while predators and shredders increased. Correlation analysis showed that water depth and mean velocity were two parameters significantly affecting the distribution of macrozoobenthos. The distribution patterns of different groups were various. Oligochaetes and chironomids prefer slow flow and deep water, and there is little difference in the optimum range of water depth and mean velocity between them. Gastropods prefer shallow and slow flow, and both the optimum range of water depth and mean velocity are narrow, while bivalves are opposite. Other aquatic insects, polychaetes and gammarids are suitable for a wide range of water depth and a relatively narrow range of mean velocity. The results provide basic information for the research of environmental flow requirement of macrozoobenthos, reservoir ecological regulation and other protection and management work in the mid-lower mainstem of the Yangtze River.