Comparative analysis of the energy fluxes and trophic structure of polyculture ecosystems of Portunus trituberculatus based on Ecopath model

This study investigated the energy flow and trophic structure of different polyculture ecosystems of the swimming crab Portunus trituberculatus using an Ecopath with Ecosim (EwE) model. Specifically, we aimed to characterize the trophic structure and biomass interactions, in parallel to assessing the energy utilization efficiency, of different ecosystems. Four treatments were designed, including the monoculture of P. trituberculatus (P), bi-species polyculture of P. trituberculatus with white shrimp Litopenaeus vannamei (PL), tri-species polyculture of P. trituberculatus with L. vannamei and short-necked clam Ruditapes philippinarum (PLR), and qua-species polyculture of P. trituberculatus with L. vannamei, R. philippinarum, and Gracilaria lichenoides (PLRG). Fourteen, 16, 17, and 18 functional groups were incorporated into models of the P, PL, PLR, and PLRG ecosystems, respectively. Macrozooplankton, macrobenthos, and Aloidis laevis consistently shared high keystoneness in all ecosystems, generating both bottom-up and top-down effects in all four ecosystems. Most of the total system throughput (TST) of the four ecosystems was distributed in trophic level I and II. The main energy flows were associated with benthic bacteria, bacterioplankton, L. vannamei, and P. trituberculatus in the PL, PLR, and PLRG ecosystems. The PLRG ecosystem has higher redundancy and overhead values than the other three ecosystems, indicating a stronger ability of resisting external perturbations. Overall, the PLRG ecosystem expressed the highest energy utilization efficiency, highest energy exports, and strongest ability of ecosystem stability among the four eco-systems, representing a sustainable P. trituberculatus polyculture pattern.