Biodiversity and Biological-Environmental Relationships of the Demersal Fish Assemblage in the East China Sea in 2008 Summer

The East China Sea (ECS) was characterized by nutrient-rich condition, high primary productivity and high fishery yield, due to the massive input of nutrient from Changjiang (CJ). However, the anthropogenic nutrient load from CJ has increased over 10-fold since 1960’s, and caused frequent eutrophication and hypoxia events. In addition, construction of Three Gorges Dam has been proved to reduce the nutrients discharge. The effects of present nutrient status on the benthos assemblage were still obscure. Nevertheless, we presume that the nutrient status in the ECS is still excessive, and may injure the benthos communities in the ECS. To verify our assumption, oceanographic survey was conducted across the inshore-offshore transects. Totally 3935 dermal fish including 71 species were collected by the beam trawl. Fish species composition varied greatly between northern and southern sites as well as between inshore and offshore sites. Higher diversity appeared at offshore sites and lowest diversity occurred at the inshore site close to Changjiang Estuary. The fish community structure among each site was related to depth, latitude, dissolved oxygen, PO4 and NO2. Besides, the fish species diversity is significantly positive correlated to dissolved oxygen and negative to concentrations of various nutrients and chlorophyll a. This result implied that the fish communities were not only determined by specific biogeographic distribution, but also by the nutrients and hypoxia conditions. In conclusion, the nutrient status in the ECS is still redundant, and its follow up consequences, including organic matters accumulation and benthic hypoxia have negatively impacted the community of demersal fish.