Influence of large reservoir operation on change patterns of fish community assembly and growth adaption at low and high-water levels

Abstract

The Three Gorges Dam is the largest water conservancy project in the world, and the Three Gorges Reservoir Area (TGRA) possesses precious fish resources. Currently, due to the lack of efficient biodiversity monitoring tools, the precise evaluation of fish community composition in a riverine reservoir has been restricted. Here, we investigated fish resources using 12S-rDNA barcoding in the TGRA before and after 175 m water level during the first year of a 10-year Yangtze fishing ban. Our results showed that the fish composition exhibited obvious seasonal differences. The environmental water levels, land use, and spatial characteristics less influenced the development of fish communities. Based on Infer Community Assembly Mechanisms (iCAMP) by phylogenetic bin-based null model analysis, 66.12 % of unexplained variables were driven by stochastic processes of community assembly and unmeasured key factors. We developed a growth-limiting index (GLI) and firstly applied it to inferring fish environmental adaptability, revealing the growth adaption response of reservoir fish species to environmental pressure. Compared to the downstream from the dam, fish population growth at the low- or high-water levels was partly inhibited. However, seven species of tiny or medium-sized fish showed strong adaptability in the reservoir region at both water levels. Taken together, this study clarified the patterns of fish community assembly in the TGRA and provided unique insights for chronic monitoring of fish diversities in a reservoir.