Model-based analysis of the energy fluxes and trophic structure of a Portunus trituberculatus polyculture ecosystem

ABSTRACT: We constructed a quantitative Ecopath model of a trophic network to evaluate the energy flow and properties in a polyculture ecosystem containing 4 species (swimming crab Portunus trituberculatus, white shrimp Litopenaeus vannamei, short-necked clam Ruditapes philippinarum, and redlip mullet Liza haematochila) over a 90 d experimental period. The model contained 10 consumers, 4 detritus groups, and 4 primary producers. Ecotrophic efficiency values indicated that the system had high energy utilization efficiency. However, benthic bacteria converted the largest amount of energy back to the detritus groups, which had the lowest ecotrophic efficiency (0.01). When aggregating the network to discrete trophic levels (TLs), most of the throughput and biomass of the system were distributed on the first 2 TLs; consequently, there was high energy transfer efficiency between TL I and II (81.98%). The trophic flow of this ecosystem was dominated by energy that originated from the detritus groups (73.77%). Imported artificial food was particularly important for the trophic flow of the total ecosystem, contributing 31.02% to total system consumption. The trophic network of the polyculture ecosystem had a moderate Finn’s cycling index (17.44%), a relatively low connectance index (CI: 26.70%), and a low system omnivory index (SOI: 0.08). Relative ascendancy was estimated as 44.90% in this model. Overall, ecosystem properties (i.e. CI, SOI, and relative ascendancy) showed that the artificial 4-species polyculture system represents a simple and fragile, but also ‘balanced,’ ecosystem.