Benefits from removing fouling mussels in suspension oyster aquaculture: An evaluation using farm-scale carbon budget and bivalve growth models

We propose a model-based approach to evaluate how effectively removing fouling mussels enhances the growth of cultivated oysters and reduces biodeposition, which could potentially lead to adverse effects on benthic environments in suspension farms. This approach links a simplified model estimating the budget of suspended particulate organic carbon (POC) in a farm with dynamic energy budget models that calculate the growth of cultivated oysters (Crassostrea gigas) and fouling mussels (Mytilus galloprovincialis). By simulating the effect of mussel removal using hot-water treatment conducted in an oyster farm in northeastern Japan, we estimated that treatment at the 12th month after the start of cultivation would increase the soft body weight of oysters harvested at the 18th month by 11 % compared to the no-treatment case. Mussel removal was also predicted to reduce the bivalves' biodeposition to 19 %. Further estimations across assumed wide ranges of background POC concentrations (up to 1.5 mg-C L⁻¹) and fouling-mussel density on cultivated oysters (up to 100 individuals per oyster) indicated that mussel removal more effectively enhanced oyster growth (by over approximately 5 %) in intermediate POC concentrations (0.02 to 0.2 mg L⁻¹) and relatively higher mussel densities (>10 individuals). The percentage of reduced biodeposition due to mussel removal was higher in relatively lower POC concentrations. The proposed models can predict the benefits of removing fouling mussels in oyster aquaculture—namely, increased oyster production and reduced environmental impact—considering site-specific conditions. These models can help determine the necessity of costly biofouling controls.