Spatio-temporal variations in functional redundancy of fish communities in the Haizhou Bay and its adjacent waters.

To explore the functional redundancy and better understand the stability of fish community in the Haizhou Bay and its adjacent waters, we examined the temporal and spatial variations in functional redundancy of fish community and the influencing factors using functional redundancy index (FR) and correlation analysis based on fish resource survey data in spring and autumn from 2013 to 2023. The results showed that the average value of FR was 9.39 in autumn and was 8.62 in spring. Fish community was more stable in autumn than in spring. There were significant seasonal differences in FR in 2015, 2016, 2018, and 2023. The FR of fish community showed interannual fluctuation, which was more significant in autumn. In autumn, the highest FR (10.36) was found in 2021, while the lowest value (8.61) was found in 2020. In spring, the highest value (9.64) was presented in 2022, and the lowest value (7.96) was in 2018. The FR increased from north to south in spring in most years, and the values were generally higher in the shallow waters less than 20 m in depth, but decreased from the southwest to northeast in most years in autumn. The spatio-temporal variations in functional redundancy may be related to fish biomass, number of species, and environmental factors such as water temperature, salinity and depth. The FR was positively correlated with fish biomass, number of fish species, and water temperature, but negatively correlated with salinity and depth.