Energy Network Analysis And Fish Community In Adjacent Waters Of Yangtze Estuary

In the research, we developed mass-balance models for Yangtze Estuary to analyze energy flow of the ecosystem based on marine comprehensive survey in 1985-1986 and 2004, respectively. By using Ecopath model, we evaluated the overall characteristic of Yangtze Estuary ecosystem in 1985-1986 and 2004. The passage also applied species diversity indices and multivariate statistical methods to analyze data collected from bottom trawl survey and environmental investigation in Yangtze Estuary and its adjacent waters in May and November 2014. Based on the analysis, the research identified species diversity, structure of fish communities as well as their relationships with environmental factors in Spring and Autumn.Organisms were divided into sixteen functional groups in the ecosystem in 1985-1986. The Ecopath model suggested that in 1985-1986 the trophic level of functional groups ranged from 1 to 4.52. Trophic aggregation analysis showed that the ecosystem was dominated by the grazing food chain in 1985-1986. A linear food chain was derived from the mixed trophic network with a mean transfer efficiency of 12.4%, 12.9% from detritus and 12% from primary producer within the ecosystem. In this period, the total system throughput is 5020.886 t/(km2·a). The evaluation of characteristic of ecosystem in this period showed that the Connectance index and system omnivory index were 0.471 and 0.103, The Finn cycling index and mean path length were 9.35% and 2.778, the ratio of total primary production and total respiration was 1.724 in the ecosystem.Organisms were divided into seventeen functional groups in the ecosystem in 2004. The Ecopath model suggested that in 2004 the trophic level of functional groups ranged from 1 to 4.34. Trophic aggregation analysis showed that the ecosystem was dominated by the grazing food chain in 2004, with 56 percent of energy derived from primary producer. Benthos and crabs energy mainly came from detrital food chain. A linear food chain was derived from the mixed trophic network with a mean transfer efficiency of 14.7%, 13.9% from detritus and 15.2% from primary producer within the ecosystem in 2004. In this period, the total system throughput is 6342.081 t/(km2·a). The evaluation of structure and function of ecosystem in this period showed that the Connectance index and system omnivory index were 0.539 and 0.069, The Finn cycling index and mean path length were 4.2% and 2.461, the ratio of total primary production and total respiration was 2.527 in the ecosystem.The research indicated that there were 28 fish species captured in May 2014, belonging to 22 families, 10 orders and 1 classes. Juvenile bluefin searobin, small yellow croaker and hairfin anchovy prevailed in fish community. In November 2004, the research indicated that there were 32 fish species captured in the survey, belonging to 22 families, 9 orders and 2 classes. Bumalo, Hairtair and hairfin anchovy prevailed in fish community. In spring, the Shannon diversity index, Margalef species richness index and Pielou evenness index ranged from 0.9 to 3.26, 0.89 to 2.72 and 0.32 to 0.92, respectively. In Autumn, the Shannon diversity index, Margalef species richness index and Pielou evenness index ranged from 0.56 to 2.57, 0.84 to 2.53 and 0.17 to 0.79, respectively.In spring, fish community may be divided into three groups, the western community, the northeastern and southern community and the southeastern community in Yangtze Estuary and its adjacent waters. In autumn, fish community may be divided into three groups, the southeast community, the western community and the northeast community in Yangtze Estuary and its adjacent waters. Canonical correspondence analysis demonstrated that the bottom pH, bottom dissolved oxygen, surface chemical oxygen demand, surface total Nitrogen and bottom total Nitrogen were the most significant environmental factors affecting fish community in Yangtze Estuary and its adjacent waters in Spring. While, the depth, sea surface salinity and bottom dissolved oxygen were the most significant environmental factors affecting fish community in Yangtze Estuary and its adjacent waters in autumn.