Sustainable growth of non-fed aquaculture can generate valuable ecosystem benefits Ecosystem services

Investment in extractive or ‘non-fed’ aquaculture has been proposed as a partial solution for sustainable food provision. An important aspect is the potential for aquaculture-environment interactions to influence the provision of ecosystem services. Here, we quantify and monetise the impacts of bivalve and seaweed farming on a regulating service (removal of nitrogen from nearshore waters) and a supporting service (habitat provision for species with fisheries value). We estimate that on average, 275–581 kg N ha−1 yr−1 (in harvest units: 4–25 kg N t -1) is removed via bioextraction at oyster, mussel and seaweed farms, with much smaller contributions from enhanced sediment denitrification beneath farms compared to reference sites. Based on nitrogen offset values in the United States and Europe, this additional nitrogen removal could be worth 84–505 USD t−1 in locations where nutrients are a management priority. Additionally, the habitat structure offered by aquaculture is estimated to support 348–1110 kg ha−1 yr−1 of additional fish compared to reference habitats, potentially worth an additional 972–2504 USD ha−1 yr−1 to commercial fishers or 1087–2848 USD ha−1 yr−1 to recreational fishers. Habitat values assume equal mortality rates at farms and comparable natural habitats, although the direction of effect is robust to small increases in mortality at farms. New policy perspectives may improve the capacity of non-fed aquaculture to sustainably meet the increasing demand for food while enhancing the provision of these two ecosystem services. Responsible development will be crucial to ensure that ecological benefits are not eroded by suboptimal site selection or farming practices that diminish the same or other ecosystem services.