[Spatio-temporal variations of functional diversity of fish communities in Haizhou Bay.]

As the link among species, ecological environment, and ecosystem function, functional diversity can help us to better understand the relationship between biodiversity and ecosystem function. We analyzed functional diversity with thirteen functional traits reflecting the characteristics of food acquisition, locomotion, ecological adaptation, reproduction and population dynamics of fish species. The seasonal, interannual and spatial variations of functional diversity of fish communities were examined using functional richness index (FRic), functional evenness index (FEve), functional divergence index (FDiv) and community weighted mean index (CWM) based on the data from the bottom trawl surveys in spring and autumn from 2011 to 2017 (except 2012) in Haizhou Bay. The results showed that functional diversity indices were significantly different in spring and autumn, with FRic was significantly higher in autumn than that in spring and FDiv was significantly higher in spring than that in autumn. Migration might be the main reason for the seasonal change of functional diversity indices. CWM analysis showed that dominant fish species were cold-temperate or warm-temperate species, with higher trophic level, strong motion ability, and relatively high growth coefficient, resilience and vulnerability in spring. In autumn, the dominant species showed the opposite traits. In both spring and autumn, fish species with pelagic eggs dominated the fish communities. Inter-annual variations in functional diversity indices were observed in spring and autumn. The functional diversity indices showed an annual fluctuation during the study period in both spring and autumn, indicating the low stability of fish community in Haizhou Bay. Significant spatial changes in functional diversity of fish assemblages were observed, with FDiv being higher in the offshore coastal waters (>20 m) than that in the shallow waters (<20 m). The functional diversity showed obvious spatio-temporal variation. The ecological niches and resource utilization of fish species varied with season, year and space in Haizhou Bay.