Seaweed aquaculture is a growing blue sector that provides many benefits to society (e.g. biomass provision for food, feed and cosmetics) and the environment (e.g. eutrophication mitigation, carbon uptake and habitat provision). Successful and sustainable production expansion requires that these activities are operated within limits of acceptable change (LAC) i.e. align with ecological and social carrying capacity. Emerging from a three-round Delphi study, this work presents, from a Global North perspective, the most relevant 1) limiting variables from the socio-environmental spheres that influence the cultivation unit (inputs), such as high operating costs or underdeveloped markets or uncertain impacts from climate change, and 2) the negative impacts of aquaculture on environment and society (outputs), such as overhyped and unrealistic expectation for seaweed cultivation, conflicts with fisheries or pollution. Consolidated lists of these inputs and outputs are accompanied by specific thresholds beyond which unacceptable changes are likely to occur. These results are placed into a globally applicable holistic framework for a multidimensional assessment of seaweed aquaculture including barriers and carrying capacity, which has been outlined for the first time for seaweed cultivation. Our results emphasize the need to include socio-economic aspects into ecosystem approaches, like profitability or social license to operate-and the need for broad stakeholder participation. This study provides thus a directly useable lists of aspects to consider for cultivators and decision-makers. And as is as such a crucial contribution for the ongoing discourse on sustainable growth of this emerging blue sector.

Offshore wind energy development has been accelerating at a rapid pace around the world to address renewable energy goals. As a new use of ocean space, offshore wind developments can create spatial and temporal conflicts with existing ocean uses. The concept of multi-use, which spans from promoting co-existence of uses to identifying synergies between uses, has become an important framework for marine spatial planning and offshore renewable energy development in Europe, where offshore wind farms have been integrated with aquaculture and tourism, among other uses. In the United States, however, where offshore wind energy is at a more nascent stage, multi-use concepts have not been applied to the planning, permitting, and development processes, and multi-use has been considered on a more ad hoc basis. Offshore wind development in the U.S. has consequently been rife with conflict, particularly with the commercial fishing industry, and a lack of consistent policy on multi-use has led to missed opportunities to consider ways to build on synergies. To better understand the state of multi-use in the U.S., we interviewed key informants in the Southern New England region from federal and state agencies, and development, research, conservation, and fisheries sectors. Based on the interviews, we identified perceived opportunities and barriers to multi-use among interviewees, and perceptions of the state of multi-use. Responses were used to share lessons learned in the region, and to develop a set of recommendations related to the implementation of multi-use policies in the U.S.

Ocean Multi-use (MU) has gained significant attention as an approach with great potential to promote a more sustainable and space efficient' Blue Economy development. Despite many efforts to implement the multi-use concept into practice, MU still has many practical challenges, which is even more evident outside the European context, where there is significant policy support for MU. This paper aims to elucidate how MU can bolster the local blue economy, particularly within the context of the Global South. The research is based on a case study in southern Brazil, within a traditional fishing community that occupies a marine protected area. A practical analysis of the synergies between community-based tourism, artisanal fishing and conservation was done through interviews with key stakeholders. The main benefits, constraints, opportunities, and risks of MU activities were identified. Results demonstrate the positive impact of MU promoting revenue, environmental education, and cultural and historical attributes. MU has shown great positive impact on social, economic, and environmental aspects within this case study. Key enabling factors that allowed the MU development were horizontal participatory governance and the protagonist of fishers. In terms of existing challenges, the absence of investment in infrastructure, fragmented governance and lack of institutional support was pointed out as the main constraint and limitations to strengthening MU. We argue that MU can be an important strategy for promoting the local blue economy. In the Global South context, the efficacy of MU initiatives appears intricately tied to the participation of local actors in a manner tailored to local contexts and challenges.

Livestock supply chains contribute a substantial share of global anthropogenic greenhouse gas (GHG) emissions, with enteric methane (CH₄) from ruminants being a key driver. Seaweed-derived feed additives have been proposed as a CH₄ mitigation strategy, but their broader environmental trade-offs remain unclear. This study applies life cycle assessment (LCA) to evaluate seven seaweed-supplemented scenarios across beef, dairy, and sheep production, assessing climate change, marine and freshwater eutrophication, land use, fossil fuel depletion, and water use. Results indicate that while certain seaweed additives can lower CH₄ emissions in vitro, real-world reductions in total GHG emissions remain modest. Energy-intensive processing and long transport distances can offset CH₄ abatement gains, with only scenarios utilizing low-impact by-products achieving net climate benefits. Sensitivity analyses highlight the importance of Global Warming Potential (GWP) time horizon selection, energy sources, and grazing practices in determining overall environmental performance. Optimizing algae sourcing, processing, and application will be essential to realizing meaningful and scalable mitigation potential in ruminant systems. While seaweed additives can contribute to CH₄ reduction, this study concludes they will not single-handedly deliver transformative climate benefits.

The study examines the governance of low trophic species mariculture (LTM) using Sweden as a case study. LTM, involving species such as seaweeds and mollusks, offers ecosystem services and nutritious foods. Despite its potential to contribute to blue growth and Sustainable Development Goals, LTM development in the EU and OECD countries has stagnated. A framework for mapping governance elements (institutions, structures, and processes) and analyzing governance objective (effective, equitable, responsive, and robust) was combined with surveys addressed to the private entrepreneurs in the sector. Analysis reveals ineffective institutions due to lack of updated legislation and guidance, resulting in ambiguous interpretations. Governance structures include multiple decision-making bodies without a clear coordination agency. Licensing processes were lengthy and costly for the private entrepreneurs, and the outcomes were uncertain. To support Sweden’s blue bioeconomy, LTM governance requires policy integration, clearer direction, coordinated decision-making, and mechanisms for conflict resolution and learning.

As seaweed farming gains prominence in future blue economies, scientifically robust environmental evaluations are vital. Harmonizing life cycle assessment (LCA) studies provides nuanced insights, allowing generalizations and potentially more accurate results than individual studies. This study recalculates life cycle inventory (LCI) data to offer a comprehensive perspective on sugar kelp Saccharina latissima. The findings affirm and validate previous studies, emphasizing critical hotspots such as fuel use for boats at sea, impacts from the use of plastic ropes, buoys and metal components at sea, and electrical energy use in the hatchery. The overall environmental impacts of seaweed farming remain relatively low compared to other seafood and biomass sources. The study also highlights the importance of how fuel use is modelled for the outcome. While harmonization enhances certainty and facilitates robust comparisons, challenges arise from the lack of standardized methods for data collection and reporting, along with data gaps between studies. Addressing these limitations calls for standardized protocols and improved data sharing practices in the field.

This paper offers a comprehensive, analytical, and critically informed overview of the current state of ocean multi-use research. It delves into the origins, trajectory, and driving forces behind this emerging research field, all within the broader context of investigations addressing the management of increasingly diverse and intensifying activities at sea. The Bibliometrix R package is employed to analyze the social, geographical, and conceptual dimensions of multi-use scientific production. The results obtained are then compared to a larger corpus of publications focusing on both multiple-use Marine Protected Areas (MPAs) and Marine Spatial Planning (MSP). Finally, the paper addresses research gaps, with a particular emphasis on the transdisciplinary challenges associated with translating this new marine policy concept into practical implementation and extending its application beyond European seas.

The versatility of microalgae biomass as candidates for various products and bioremediation needs motivates interests towards design and implementation of novel microalgae bioreactors. Conventional open-reactors are reliant on large quantities of sunlight and space while yields are constrained by outdoor environment conditions. Conversely, closed-reactor systems like bubble columns reduces these constrains on microalgae growth while occupying far less space at the expense of high energy demands, notably from lighting systems. A novel patented closed reactor design has recently been proposed that improves the bubble column concept with an efficient and effective lighting system. The present study uses Life Cycle Assessment approach to compare the environmental performance of conventional reactors and the proposed internally luminated novel closed reactor design, expressing impacts per kg biostimulant for the Scenedesmus almeriensis harvest from such units. All performance data was collected from a pilot facility in Almeria, Spain. Urban-industrial symbiosis scenarios are also portrayed in the study using wastewater and incinerator flue gas. Results show that under synthetic nutrient and carbon inputs in Spanish pilot operations, the cumulative energy demand for the novel photobioreactors is similar to conventional vertically-stacked horizon bioreactors but are substantially more demanding than conventional open reactors. However, when leveraging renewable energy sources and the photosynthesis process to consume wastestreams in urban-industrial symbiosis scenarios, the novel photobioreactor was able to achieve up to 80 % improvements in several impact categories e.g. eutrophication and climate change. Impact mitigation credits per kg dwt biomass across all energy scenarios in symbiosis amount to asymptotic to 1.8 kg CO(2)eq and asymptotic to 0.09 kg PO4 eq. This highlights that such closed and internally illuminated photobioreactors can be competitive with conventional reactors, and have potential to harness photosynthesis to reduce environmental burdens in an urban-industrial symbiosis setting. Possible economies of scale and the associated potential gains in efficiencies are further discussed.

The environmental benefits of seaweed cultivation have gained a lot of attention, both in policy strategies and by private companies. Sustainability evaluations of seaweed farming have however focused on a very small part of global production of seaweed - on European cultivations at research and pilot-scales although Asia stands for 99 % of global production with China alone producing 60 %. In this study, we use Life Cycle Assessment (LCA) to evaluate the environmental performance of a 400-hectare Chinese kelp farm with a yearly harvest of 60,000 tons. Primary data from the farm was used to assess impacts up until harvest for the functional unit of 1 ton of fresh-weight kelp. Included in the LCA were impact on climate change, acidification terrestrial and marine eutrophication, and use of land water and energy. In addition, we calculated nutrient uptake. Further, we extracted inventory data of four published LCA studies of farmed kelp and recalculated environmental impacts, applying the same background data and method choices with the aim to compare the effects of scale and cultivation system. The results of the hotspot analysis showed that the plastic ropes and buoys dominated impacts on climate change, freshwater and marine eutrophication, and energy consumption. Consequently, the most effective improvement action was recycling after use. The yearly harvest of the Chinese farm was 1000–4000 times larger than previously evaluated farms compared. Results suggest that streamlined and mature production in the large-scale Chinese kelp farm led to lower electricity and fuel consumption compared to small-scale production, thus placing the Chinese farm with a climate impact of 57.5 kg CO2 eq. per ton fresh-weight kelp on the lower end when comparing the carbon footprint. There was a large variation in carbon footprints, which implies that the kelp cultivation sector has considerable room for optimization.

Seaweed is often touted as a blue economy resource with climate benefits. Several calls are made to scale the industry up and to use blue carbon financing to create additional incentives for the sector to expand. But how much of a climate crisis panacea is seaweed, and under which conditions can climate benefits be realized? The article reviews the literature on climate impacts from seaweed value chains and proposes a cradle-to-grave structure for carbon accounting in seaweed value chains. While the literature points towards several ways in which climate benefits can be generated, the evidence base for net negative emissions across the value chain is not robust enough to suggest seaweed value chains, by default, are a climate solution. Instead, climate effects depend on the specific production setup, product choice and the fate of the product on the market. Climate benefits can only be claimed by tracking blue carbon flows across whole life cycles and over time. Knowledge gaps relate to effects at sea, the role of temporarily locking carbon into products and the effects of introducing this resource to the market. Blue carbon financing should be directed only to setups proven to lead to additional and permanent carbon storage.