Using the Ecopath modeling software,the energy flow model of Mercenaria mercenaria-Portunus trituberculatus-Litopenaeus vannamei polyculture pond ecosystem was constructed.The model contained 12 functional groups.The carrying capacity of M.mercenaria was evaluated based on the energy flow model.Results show that M.mercenaria showed the highest biomass(134.99 g/m2),followed by L.vannamei(62.56 g/m2)in the ecosystem,and the zoobenthos showed the highest trophic level(TL)(2.65).Due to the low energy transfer efficiency(5.20％)between TL Ⅱand Ⅲ,most of the energy throughput(98.37％)was distributed in TL Ⅰ and Ⅱ.The system connectance index and omnivory index were 0.37 and 0.05,respectively,indicating that the food web structure of the ecosystem was very simple.The ratio of total primary production to total respiration was 2.13,and the net system production was 715.18 g/m2 in every 30 d,indicating that the ecosystem was mainly autotrophic.The imported artificial feeds accounted for 71.60％of the primary production,which made the ecosystem food web mainly dominated by detritus food chain.The results evaluated in Ecopath model show that the ecological and production carrying capacity of M.mercenaria were 854.46 and 1441.47 g/m2,respectively,in the polyculture ecosystem.The stocking density of M.mercenaria was calculated as 73 and 123 ind/m2,respectively,based on the ecological and production carrying capacity.The Ecopath model is not able to simulate inorganic processes;therefore,caution should be made while using the results estimated by Ecopath.Maintaining the water and bottom environment within the appropriate range for cultured organisms is an important prerequisite for the correction of the evaluated results of Ecopath.
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