Integrating sustainable bivalve aquaculture into water quality strategies to mitigate anthropogenic nitrogen loads.

Excessive nitrogen runoff from agricultural and urban sources poses a significant threat to coastal ecosystems. Elevated dissolved inorganic nitrogen (DIN) levels contribute to algal blooms, hypoxia, and coral degradation, undermining the health and resilience of the reef system. In addition to land-based management, bivalve aquaculture has been proposed as a potential solution for mitigating nitrogen loads in coastal environments. However, studies assessing the suitability, scale, and potential benefits of such production for reducing impacts of nitrogen runoff are often lacking. This study evaluated the potential of bivalve aquaculture (tropical black-lipped oyster, (Saccostrea echinata)) to mitigate DIN loads using a case study of the Great Barrier Reef (GBR). By combining spatial information on environmental, biophysical, and socio-economic constraints, we identified 818.9 km2 of suitable bivalve aquaculture area along Queensland's coastline. Developing just 43% (352.9 km2) of the suitable area could remove 77.9% (4145 tonnes) of the GBR's total anthropogenic load, closing the critical nutrient management gap left by currently insufficient land-based mitigation measures. Economically, this could translate to a potential AUD $809.7 million in oyster market value and AUD $871.6 million in Reef Credits for nitrogen annually. These findings highlight the potential for bivalve aquaculture to contribute meaningfully to regional water quality targets by complementing land-based management measures. Our model and results can inform planning and investment decisions by policymakers, regulators, and industry, both within Australia and in other coastal regions facing similar challenges of nitrogen pollution and climate-resilient food production.