Spatial and temporal variations of demersal fish assemblages in the East China Sea in 2010 to 2012

In order to understand the demersal fish assemblages and its link to the environments, beam trawl surveys and hydrographic measurements were conducted across the East China Sea continental shelf in 2010 - 2012. The results suggested that the fish assemblages varied with the depth and salinity gradients with significant difference in composition between inshore and offshore areas. Water temperature might be an important factor in shaping the spatial pattern during spring and autumn periods. Bio-indices (e.g. diversity, richness and evenness) showed negative correlations with Chl. a concentrations and nutrients levels and positively correlated with dissolved oxygen. The eutrophication and subsequent hypoxia in the inshore area during summer periods favored the high dominance of opportunistic species (Amblychaeturichthys hexanema). These results suggested the negative impacts of eutrophication and hypoxia on the demersal fish assemblages. Seasonal changes of fish compositions were only found in the inshore area, which may attribute to the succession of dominant species. In addition, we found moderate recovery of fish communities after summer hypoxia but the short-periods of alleviation from stressful condition might not be adequate to compensate the simplified assemblages during hypoxia. Despite the variation of primary productions in different seasons, d13C value of fish muscle suggested that in situ primary production was the main food sources to the demersal fish rather than the terrestrial POM. d15N of demersal fish were higher in autumn than in summer, which might attribute to the preferential uptake of isotopic lighter N source or the shift in baseline rather than elongation of food chain. Our results provided further insights into the demersal fish assemblages in the ECS, and the influences of environmental parameters on fish compositions.