A mass-balanced model was constructed to determine the flow-energy in a community of fishes and invertebrates in the Beibu Gulf,northern South China Sea using Ecopath and Ecosim software. Input parameters were taken from the literature, except for the biomass of fish groups which was obtained from trawl surveys during October 1997 to May 1999 in the study area. The model consisted of 16 functional groups (boxes), including one marine mammal and seabirds, each representing organisms with a similar role in the food web, and only covered the main trophic flow in the Beibu Gulf ecosystem. The results showed that the food web of Beibu Gulf was dominated by the detrital path and benthic invertebrates played a significant role in transferring energy from the detritus to higher trophic levels; phytoplankton was a primary producer and most utilized as a food source. Fractional trophic levels ranged from 1.0 to 4.08 with marine mammals occupying the highest trophic level. Using network analysis, the system network was mapped into a linear food chain and six discrete trophic levels were found with a mean transfer efficiency of 16.7% from the detritus, 16.2% from the primary producer within the ecosystem. The biomass density of the commercially utilized species estimated by the model is 8.46 t/km2, only 0.48% of the net primary production.
South China Sea Fisheries Research Institute, Chinese Academy of Fisheries Sciences, Guangzhou 510030, China;College of Marine Science and Technology, Shanghai Fisheries University, Shanghai 200090, China;Key Laboratory for Sustainable Utilization of Marine Fisheries Resources of the Ministry of Agriculture, Qingdao 266071, China
South China Sea Fisheries Research Institute, Chinese Academy of Fisheries Sciences, Guangzhou 510030, China