Community diversity patterns of freshwater mussels (Unionida) in Shijiu Lake and its connected channels during the early period of the Yangtze River fishing ban

To assess freshwater mussel community diversity and its environmental drivers in Shijiu Lake and the connected Guxi River during the early stage of the Yangtze River’s ten-year fishing ban, systematic surveys were conducted in August–September (high-water period) and November–December (low-water period) of 2024. A total of 68 transects were established and sampled twice. Twenty-two mussel species from 15 genera of the Unionidae were recorded, including 12 species endemic to China, such as the nationally protected Aculamprotula fibrosa and Lamprotula leai . The overall mussel density and biomass were 0.071 ± 0.047 ind./m² and 10.862 ± 12.067 g/m², respectively. Shijiu Lake supported significantly higher biomass (17.167 ± 12.770 g/m²) and density (0.077 ± 0.039 ind./m²) than the Guxi River (2.880 ± 3.203 g/m² and 0.064 ± 0.056 ind./m²), whereas the river exhibited higher species richness (Margalef index = 3.270) and diversity (Shannon–Wiener index = 2.483) than the lake (2.846 and 2.118, respectively). Dominant taxa differed between habitats, with Cristaria plicata and Sinanodonta woodiana prevailing in the lake, and Schistodesmus spineus and Lamprotula caveata in the river. Redundancy analysis identified flow velocity as the most influential environmental factor shaping species distribution ( P < 0.05), while species exhibited differential adaptations to water depth, substrate type, and flow velocity. Abundance–Biomass Comparison curves and Normalized Biomass Size Spectra indicated higher community stability in Shijiu Lake and moderate disturbance in the Guxi River. Compared with historical data, mussel communities in Shijiu Lake showed signs of recovery, with increased diversity under the fishing ban and ongoing ecological restoration. These findings highlight the effectiveness of fishing bans in restoring freshwater biodiversity and provide insights into conservation strategies for river–lake ecosystems subject to hydrological modification worldwide.