Modeling assessment of carrying capacities of kelp and bivalve polyculture bay based on ecological model

Large-scale, high-density mariculture has developed rapidly, and assessing its carrying capacity (CC) is important for sustainable development. Taking Sanggou Bay (China), a typical kelp-bivalve polyculture bay, as the study area, we develop an ecological model that incorporates the effects of aquaculture on hydrodynamic-biochemical processes and establish the CC model based on the food-balance relationship, so as to assess the CC of kelp and bivalve and determine reasonable culture densities. By incorporating the momentum loss caused by aquaculture, we achieve modeling hydrodynamic processes in culture waters. This shows that aquaculture alters the vertical structure of water-currents and significantly reduces the water-exchange ability (the bay’s half-exchange duration is ∼16 d with bivalve-kelp cultures and ∼7 d without aquaculture). The model reflects aquaculture’s impact on the ecosystem and reproduces ecological characteristics, including a weak phytoplankton biomass peak in February and the highest peak in September (3.7 μg/L on average). We estimate the CC in the kelp culture zone to be 3.84 ind/m² and propose maintaining the stocking density at 4 ind/m². We present the dynamic variations of bivalve CCs for different specifications. The CC of scallops is low in spring and summer, reaching its lowest in mid-April. The annual average CC for the mean size is 53 ind/m² (35,333 ind/acre), and the density of 59 ind/m² should not be exceeded. The CC of oysters is low in summer, reaching a minimum in late August. The theoretical capacity of the mean oyster is 76 ind/m² and we propose maintaining a density of 39,333 ind/acre.