The capacity of shellfish farming areas to act as either a carbon source or a carbon sink is determined by how closely the actual farming density approaches the local density threshold. Currently, most shellfish aquaculture zones are overstocked, exceeding the density threshold, and as a result, these areas generally function as carbon sources. Our monthly sampling data from the Shengsi mussel farming area show that, apart from exhibiting a strong carbon sink status in spring, the area is predominantly a carbon source in summer and autumn, and a weak carbon sink in winter. Moreover, the farming ground itself shows that mussels in the inner zone do not grow plump, and the carbon release intensity in the inner zone is significantly higher than that in the outer zone. When we introduced artificial upwelling (AU) into the ecosystem, we observed that by enhancing hydrodynamic exchange, AU not only transports deep‑layer algae to the surface layer where mussels can utilize them, but also promotes local photosynthesis, creating a region of high chlorophyll concentration centered on the upwelling device. Consequently, the condition (fatness) of shellfish within the influenced area is markedly improved, and the carbon release capacity of the area is substantially reduced. This indicates that AU increases the local density threshold of the farming area, thereby decreasing the amount of CO₂ emitted from the area to the atmosphere. Furthermore, if we were to further reduce the farming density to align with the threshold, the area could become a stronger carbon sink than it would be in the absence of mussel farming.