Abstract:Using the Ecopath with Ecosim software, we constructed a trophic structure model of a large enclosed sea area in north Hangzhou Bay to analyze the main biomass flows in the artificial ecosystem. The structure model is based mostly on the 2006 survey data and it provides a snapshot of how the artificial ecosystem operates. The model consists of 13 functional groups, which are piscivorous fish, benthic-feeding fish, zooplanktivorous fish, herbivorous fish, crabs, shrimp, mollusca, infauna, carnivorous zooplankton, herbivorous zooplankton, periphyton, phytoplankton and detritus. Each group represents organisms with a similar role in the food web, and the 13 functional groups cover the main trophic flow in the artificial ecosystem. The results show that the food web in a large enclosed sea area is dominated by the detrital path, and herbivorous zooplankton plays a significant role in transferring energy from detritus to higher trophic levels. Trophic levels of the compartments vary from 1.00 for the primary producers and detritus to 3.90 for the piscivorous fish. Through network analysis, the system network is mapped into a linear food chain and six discrete trophic levels are found with a mean transfer efficiency of 9.8% from detritus and 9.4% from the primary producers within the ecosystem. The geometric mean of the trophic transfer efficiencies is 9.6%. In the course of energy flow, the proportion of total flow originating from detritus is 57%, and that from the primary producers is 43%. Three indexes of ecosystem maturity, TPP/TR, FCI and Ascendancy, are 2.672, 0.25 and 0.315 respectively, indicating that the artificial ecosystem of a large enclosed sea area in north Hangzhou Bay is in the state of development. This is the first reported trophic model of a large artificially enclosed sea area; it may serve as the basis for future bioremediation and ecosystem management in eutrophic coastal sea areas.