Optimizing Culture Density to Balance Seston Transport and Mussel Growth in Gouqi Island Suspended Aquaculture

Intensive high-density suspended mussel aquaculture frequently experiences flow attenuation and limited hydrodynamic exchange, leading to severe internal food depletion. To address this issue, this study evaluates spatial density-optimization strategies to balance stocking scale and production performance in the Gouqi Island suspended aquaculture farm for the mussel Mytilus coruscus Gould, 1861. A three-dimensional hydrodynamic-tracer-bivalve growth model was developed within the SCHISM framework. This approach established a dynamic two-way coupling between tracer transport and bivalve growth, capturing feedbacks among hydrodynamic transport, facility-induced obstruction, and biological depletion. Field observations along the surveyed transects showed that chlorophyll-a concentrations within the aquaculture layer were 64.9–85.5% of those in adjacent non-aquaculture waters. Scenario simulations revealed that while uniform density reduction improved internal food availability, it substantially reduced the total stocking scale. In contrast, a spatially heterogeneous density configuration provided a more favorable balance between food availability, growth, and stocking scale among the tested scenarios. At a total stocking scale of 2.34 million sleeves, the area with tracer concentrations below 0.65 during neap tides was reduced to 620.06 ha, representing a 25.33% reduction relative to the current scenario. Additionally, an area of 174.41 ha achieved a relative individual growth increment exceeding 0.20. Ultimately, aligning culture density with local hydrodynamic transport conditions can alleviate internal food limitation while maintaining a relatively high stocking scale.