An ecosystem-based evaluation of the carrying capacity ratio for bivalve and macroalgae polyculture: a case study in...

Aquaculture is a cornerstone of global aquatic food production, yet its rapid expansion has raised growing concerns about ecological risks and water pollution. Bivalve-macroalgae polyculture, recognized for its substantial ecosystem service potential, offers diverse ecological benefits. However, misaligned culture scales and improper species ratios can drive functional imbalance and trophic bottlenecks, ultimately hindering the recovery of biological resources. Consequently, understanding how variations in culture scale and ratio influence ecosystem dynamics while also balancing ecological risks and restoration benefits is pivotal for the sustainable development of aquaculture. In this study, the Ecopath with Ecosim model was employed to simulate the effects of multiple aquaculture scenarios on ecosystem stability and functional group biomass in Sansha Bay. The results revealed that reducing the bivalve culture scale promoted an increase in the biomass of most functional groups, whereas an expansion of bivalve culture led to a decrease. Although increasing macroalgae culture reduced phytoplankton biomass, it boosted the biomass of other functional groups. When varied individually, enlarging bivalve culture or reducing macroalgae culture enhanced ecosystem stability and maturity, whereas the opposite adjustments diminished these attributes. Within the non-spatial EwE framework used here, an ecologically favorable scenario was identified when bivalve and macroalgae culture scales were reduced to 50% and 60% of their current scales, respectively; under this scenario, the biomass of most functional groups increased by 30-65%, together with improvements in ecosystem maturity and diversity. These findings provide a scenario-based, non-spatial reference for adaptive aquaculture management in Sansha Bay and similar semi-enclosed marine ecosystems, while the proposed culture levels should be further refined through spatially explicit ecological analyses and socioeconomic assessments before implementation.