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As interest in natural climate mitigation solutions continues to grow, there is an essential role for coastal and ocean ecosystems ("blue carbon") to play. To meet mitigation targets, however, it is crucial that human actions to protect or restore blue carbon sinks are based on solid science and actionable human management opportunities to increase sinks and reduce emissions from ecosystem loss. Here, we reaffirm the role of coastal wetlands in climate mitigation opportunities. We update the state of the science regarding existing blue carbon pathways and explore expanding the blue carbon opportunities to new systems. Specifically, we analyze new science for those blue carbon pathways we categorize as "emerging" (e.g., management interventions involving macroalgae - both cultivated and wild, tidal flats, and marine sediments) where human action may be able to increase these sinks, but we currently have insufficient information to ensure that their climate mitigation benefit is additional. We revisit those that are "non-actionable" (e.g., management interventions involving calcifying organisms and marine fauna) where the scientific evidence is clear that there is no mitigation benefit, or the science is too uncertain to claim that human action can definitively increase these carbon sinks. With limited funding for climate action, it is critical that efforts focus on projects with the most mitigation potential. Blue carbon management is only one piece in the climate mitigation challenge, but it is an important one. Continued scientific research and investment in developing policy pathways is warranted for these actionable and emerging systems. At the same time, the world must continue to work to decrease emissions rapidly, invest in other natural climate solutions, and scale renewable energy technologies. [ABSTRACT FROM AUTHOR]

Recent attention to the ecosystem service-generating potential of marine aquaculture (mariculture) indicates that there is substantial opportunity for marine farming to optimise practices that benefit both production and nature. One strategy for augmenting sustainability within the mariculture industry is to develop more diverse farming practices and culture species that can operate within existing ocean space constraints, contribute to ecological and conservation objectives, and assuage negative public sentiment towards mariculture. While this strategy has the potential to expand mariculture's sustainability, the implementation of these alternative culture approaches will likely depend on whether the management frameworks that regulate the industry have the authority and the capacity to enable farming innovations and encourage investment in diverse mariculture systems. Using Australia and seafloor ranching of molluscs as a case study, we explore the suitability of existing policy and legislation to support novel farming methods. We find that the policy frameworks differ across States in terms of their applicability (both implicit and explicit) to seafloor ranching activities, with substantial gaps regarding the siting and building of farming infrastructure. In the context of these results, we discuss potential strategies for leveraging existing policy and management frameworks to meet the needs of seafloor ranching and identify operational stages where new, targeted policy could be particularly impactful. Our case study offers practical insights to policymakers in Australia and other countries and regions seeking to support innovations in culture methods with a greater potential for sustainability. • Diversification can bolster sustainability within the mariculture industry. • Policy gaps could hamper operationalization of alternative farming practices. • Governance frameworks require specific consideration of alternative culture methods. • Leveraging existing policies can permit and support mariculture innovations. [ABSTRACT FROM AUTHOR]

• Farms increase removal of nitrogen from marine waters, mostly during harvest. • Farms act as nursery habitats and are projected to increase recruitment of fish to fisheries. • These regulating and supporting ecosystem services have monetary value. • Benefits to the services assessed may be worth billions of USD annually. 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. [ABSTRACT FROM AUTHOR]

Competing Interests: Competing interests: None declared.