Taxonomic and functional response of fish assemblages to flood-triggered water level fluctuations in a large floodplain lake along the Yangtze River

Water level fluctuations (WLFs) are generally regarded as the primary factor structuring the fish metacommunities in floodplain lakes, but their effects on fish taxonomic and functional diversity have been limited explored. Here, we asked how fish taxonomic and functional structures vary in response to different WLFs, and how environmental parameters influence fish metacommunity structures among different WLFs. Our results demonstrated significantly higher Richness, Pielou’ evenness, Shannon-Wiener index, functional richness, and functional evenness in high water phase, which was probably due to high fish recruitments originating from floodplain rivers. The high abundance of riverine gudgeons in high water phase confirmed the enhanced fish dispersal processes from rivers to floodplain lakes which were triggered by flood pulses. Compared to the scenario of high-water level, our results demonstrated significantly lower taxonomic and functional diversity during low water phase with more abundant generalist fish species. Such changes were probably triggered by enhanced environmental filtering during the low water phase, since we detected significantly intensified environmental loadings in low water level. Water temperature, conductivity, total nitrogen, and phosphate phosphorus were retained as significant predictors of fish taxonomic and functional structures across different water levels, which suggested that WLFs influenced fish assemblages through physicochemical changes. The present findings highlighted the importance of sustaining natural WLFs as well as seasonal floods in high water for the fish recruitments in floodplain lakes.