Harnessing seaweed farming for climate mitigation in South Korea: evaluating carbon dioxide removal potential and future research directions

Scalability of seaweed aquaculture

Scaling up seaweed aquaculture faces significant economic, environmental, and regulatory challenges. Carbon removal through seaweed cultivation remains unprofitable, while nutrient availability, light conditions, and technological limitations restrict suitable farming areas (Bak et al. 2018). From an environmental perspective, large-scale aquaculture can harm ecosystems through oxygen depletion, methane emissions, nutrient exhaustion, and habitat disruption. Some seaweed species also release halocarbons that may counteract climate change mitigation efforts (Ross et al. 2023). Furthermore, intensive cultivation risks reducing biodiversity and introducing invasive species (Corrigan et al. 2022).

Research is underway to address these challenges. Breeding programs in Asian countries have boosted yields by 75% (Boderskov et al. 2023) through advances in seaweed seed production technology and substrate research (Avila-Peltroche et al. 2022, Jiksing et al. 2022, Park et al. 2022, Jung et al. 2023). Strategic farm placement has also improved nutrient uptake and photosynthetic efficiency (Broch et al. 2019). However, carbon sequestration in seaweed farming still demands careful consideration—particularly due to varying regional regulations and the need for rigorous MRV procedures to demonstrate carbon removal effectiveness.

EEZ potential

There are approximately 48 million square kilometers of global waters suitable for seaweed farming, representing about 13% of the total ocean area and about 35% of the global EEZ area (Froehlich et al. 2019). These suitable waters are areas with limited human activity, sufficient sunlight, and nutrient-rich waters, especially those with high levels of DIC, such as the upwelling zone, which further enhances seaweed’s carbon fixation efficiency.

It is estimated that growing seaweeds in approximately 1 million km² of the most productive areas of the global EEZ could produce gigatons of biomass per year (Arzeno-Soltero et al. 2023). This is based on seaweed’s rapid growth rate, adaptability to a wide range of marine environments, and minimal freshwater and land use. In particular, innovative offshore aquaculture technologies, such as multi-trophic level aquaculture systems, have enabled expansion into deeper waters (Buschmann et al. 2017), allowing production to scale up while minimizing competition with coastal ecosystems.

Seaweed farming on a global scale not only contributes significantly to meeting CDR targets, but also provides ancillary benefits such as enhancing food security, restoring marine ecosystem habitats, and mitigating ocean acidification. This demonstrates that seaweed farming is a comprehensive marine environmental improvement strategy that goes beyond simple carbon reduction.

Offshore seaweed farming is an approach that removes carbon by growing seaweed in the open ocean and settling it in the deep ocean. A North Atlantic study by Baker et al. (2022) achieved a 94% carbon sequestration rate at depths of more than 2,000 meters. Offshore aquaculture has several advantages. The high carbon-to-nutrient ratio of seaweed allows for effective carbon fixation even in eutrophic environments, and sequestration can be achieved over 100 years at depths greater than 500 meters (Broch et al. 2019). The CDR potential is substantial due to scalability opportunities (DeAngelo et al. 2023), while monoculture conditions and minimal herbivore presence make carbon flow analysis more straightforward (Hurd et al. 2024). Offshore aquaculture presents a number of challenges from an ecosystem perspective. Complex ecosystem dynamics are involved, including seaweed-plankton competition for nutrients, interactions with calcifying organisms, and albedo effects (Ross et al. 2022).

Re-mineralization of carbon

The biggest challenge to seaweed farming is the issue of carbon re-emission. More than 90% of the carbon fixed in seaweed biomass is rapidly reoxygenated during decomposition, combustion, or short-term product use and released into the atmosphere as CO₂ (Krause-Jensen et al. 2018). To overcome this limitation, long-term carbon sequestration of harvested biomass is essential, which can be achieved through additional processing, such as biochar production or incorporation into durable materials such as composites for construction (Farghali et al. 2023, Lian et al. 2023). Without these additional processing steps, the direct contribution of seaweed farming to CDR will be limited, demonstrating the urgent need for technological innovation to improve the carbon sequestration efficiency of seaweed farming.

Meanwhile, CDR through marine afforestation and deep-sea seaweed dumping faces a number of environmental, technical, and economic challenges. Environmentally, large-scale seaweed farming can negatively impact marine ecosystems. Native plankton disturbance, food chain changes, and volatile organic compound emissions are major concerns (Levin et al. 2023), and only 30% of the world’s oceans are suitable for aquaculture due to iron deficiency (Froehlich et al. 2019). On the technical side, there are uncertainties about the effectiveness and measurement of carbon sequestration. During deep-sea processing of seaweed biomass, significant amounts can be re-emitted as CO₂ (Siegel et al. 2021), and precise monitoring of the ocean-atmosphere CO₂ equilibrium is needed to accurately measure the actual removal of CO₂ from the atmosphere. On the economic side, the sustainability of large-scale aquaculture is a major challenge. Most biomass, except for high-value markets, is uneconomic (Troell et al. 2024), and simply dumping seaweed into the deep ocean means missing out on more valuable uses, such as food, fertilizer, and cosmetics.

Operational emissions

Operational emissions from the growing, harvesting, and transportation of seaweed are a significant factor that can offset the net climate benefits of this activity. Energy used for offshore aquaculture equipment and transportation emits significant amounts of greenhouse gases (Bullen et al. 2024), which contributes significantly to the overall carbon footprint of seaweed farming. In addition, in some regions, fertilizers are used to increase productivity, which generates nitrous oxide (N₂O), an additional source of GHG emissions (Resplandy et al. 2024). Of particular note are the emissions of methane (CH₄) and halocarbons that result from the decomposition of seaweed under anoxic conditions, which can be a major factor in reducing the climate mitigation benefits of seaweed farming (Resplandy et al. 2024). Improving farming efficiency and actively incorporating renewable energy sources into operations are therefore key challenges to minimizing these emissions and maximizing the net climate benefits of seaweed farming.

MRV limitations

Rigorous scientific verification is essential to demonstrate the CDR effectiveness of seaweed farming. According to the additionality principle, carbon uptake through seaweed farming must clearly exceed the uptake in the natural state, and this must be objectively demonstrable (Pessarrodona et al. 2023). International standards require at least 100 years of stable carbon storage (Group of Experts on the Scientific Aspects of Marine Environmental Protection 2019), so the establishment of a systematic MRV system is essential to verify the effectiveness of such long-term storage (United Nations Framework Convention on Climate Change 2014).

Accurate measurement and verification of carbon sequestration through seaweed farming is severely constrained by the lack of a standardized MRV framework, with a major challenge being the quantification of the rate at which DOC is converted to RDOC and remains in the ocean for long periods of time (Buck-Wiese et al. 2023). In addition, the burial rate of POC is highly dependent on regional deposition dynamics and oxygen availability, and accurately measuring and predicting this variability is also a major challenge (Duarte et al. 2023). Tracking emissions from operations and integrating them into life cycle assessments (LCA) has also been pointed out as a key issue to be addressed (Hasselström and Thomas 2022).

In this context, the development of robust MRV systems is a prerequisite for seaweed aquaculture to be effectively integrated into carbon markets and national climate accounting systems—a key challenge if carbon reduction efforts through seaweed aquaculture are to be recognized and utilized as a viable climate change mitigation strategy.

Biochar and carbon-enhanced materials

The process of converting seaweed biomass into biochar has important implications for soil management and carbon sequestration. Biochar is stable for decades to hundreds of years when injected into soil and has been shown to improve soil fertility while effectively storing carbon (Sun et al. 2022, Farghali et al. 2023). Furthermore, the application of biochar extends to the construction industry, where its incorporation into building materials such as concrete and asphalt can contribute to reducing carbon emissions from conventional building materials while enhancing long-term carbon sequestration (Wani et al. 2022).

Bioplastics

Seaweeds are gaining attention as a raw material for biodegradable plastics because of its value as an environmentally friendly alternative to conventional petroleum-based plastics. In particular, the production process of seaweed-based bioplastics can reduce energy consumption by up to 65% compared to conventional petroleum-based plastics, which can contribute significantly to reducing carbon emissions (Lim et al. 2021, Nagarajan et al. 2024). Furthermore, due to their biodegradable nature, they can effectively prevent microplastic pollution in marine ecosystems and soils, making them an innovative solution to address two environmental challenges simultaneously: climate change mitigation and ecosystem conservation (Zhang et al. 2024).

Livestock feed additives

Adding seaweed to livestock feed has been recognized as an effective solution for reducing GHG emissions in the agricultural sector. In particular, studies have reported that adding red algae species, such as Asparagopsis taxiformis, to livestock feed can reduce methane (CH₄) emissions from ruminant gut fermentation by up to 80% (Machado et al. 2016). This is a significant reduction in enteric fermentation methane, a major source of GHG emissions from the agricultural sector, and highlights the climate change mitigation potential of seaweed farming.

Biofuels

Seaweed-based biofuels are gaining attention as an alternative to address the environmental problems caused by the use of fossil fuels. Seaweed-derived fuels, such as bioethanol and biodiesel, have the potential to reduce GHG emissions by replacing conventional fossil fuels (Jung et al. 2013). In particular, recent research has shown that integration with processing systems utilizing renewable energy enables efficient biofuel production with minimal GHG emissions during production (Farghali et al. 2023). These technological advances are further increasing the commercial viability of seaweed-based biofuels, and their role as a low-carbon energy source is expected in the future.

Carbon sequestration and emission reductions

Soil utilization of seaweed biochar shows notable carbon sequestration benefits. LCA results show that one ton of seaweed biomass (wet biomass) converted to biochar and applied to soil can result in net carbon sequestration equivalent to up to 0.06 tons of carbon dioxide equivalent (Roberts et al. 2015).

Even more noteworthy is the potential for seaweed as a livestock feed additive; specifically, the use of red algae of the genus Asparagopsis as a feed additive for ruminants on a global scale is predicted to result in GHG reductions equivalent to approximately 2.6 gigatons of carbon dioxide equivalent (CO₂e) per year (Spillias et al. 2023). This high mitigation potential is also confirmed under realistic feeding conditions: assuming a feed additive input of 7–10 kg per animal per year and a methane mitigation efficiency of approximately 80%, each ton of Asparagopsis-based additive could result in GHG reductions equivalent to approximately 200–300 tons of carbon dioxide equivalent (CO₂e).

Energy use and emissions in seaweed processing

Seaweed products have shown significant substitution effects compared to conventional products, but energy consumption during production remains a challenge. Seaweed-based bioplastics have shown energy savings of 30–50% compared to petroleum-based plastics (Ayala et al. 2023), but still rely on industrial processing, which requires further energy efficiency. The pyrolysis process for biochar production also generates significant operational emissions (Pariyar et al. 2020), which can partially offset the carbon sequestration benefits of biochar if not utilized with renewable energy sources, requiring overall improvements in the production process.

Net climate benefits

There are important limitations to the carbon sequestration effectiveness of seaweeds. Most of the carbon fixed by seaweeds remains in short-term storage, with only a very low proportion leading to long-term storage. The climate change mitigation effect is expected to be quite limited now and in the near future, especially considering that the global cultivated seaweeds area is only 0.06% of the range of wild seaweeds (Pessarrodona et al. 2024). Moreover, emissions from fossil fuel use during seaweed farming are likely to offset the carbon removal, further reducing the net mitigation effect.

Nevertheless, there are positive findings at the local level. A study of various scenarios for the coast of British Columbia (BC), Canada, found that, depending on the growth rate and utilization of seaweeds, GHG emissions reductions of 0.20 to 8.2 Tg CO2e per year are possible. This is significant, representing 0.3 to 13% of BC’s annual GHG emissions (Bullen et al. 2024). Notably, the analysis suggests that effective substitution of existing carbon-intensive products is more important than ocean sequestration to achieve these climate benefits. However, the realization of these potential benefits is dependent on a number of factors, particularly technical and operational factors such as energy use, emissions from transportation, and the efficiency of the product conversion process, which have been identified as crucial to actual reductions.

Energy and infrastructure requirements

The production of value-added products from seaweeds is accompanied by significant energy consumption, which has a significant impact on the efficiency and sustainability of the overall process (Lian et al. 2023, Liu et al. 2024). It is important to note that the climate change mitigation benefits of utilizing seaweeds can be significantly reduced if conventional fossil fuel-based energy sources are continued to be used, especially during processing. In addition, many regions currently lack the necessary infrastructure for large-scale seaweed cultivation and processing, which is a major factor limiting the expansion and efficient operation of the seaweed industry.

Economic feasibility

The high cost of growing and processing seaweeds is currently a major economic barrier. In particular, when compared to traditional feedstocks such as petroleum or synthetic fertilizers, seaweed-based products have been shown to be significantly less cost-competitive (DeAngelo et al. 2023). To address these cost issues and ensure the sustainable growth of the industry, it is essential to achieve economies of scale through the establishment of large-scale production systems. If economies of scale are realized, it is expected that unit production costs can be significantly reduced.

Product market penetration

Market access for seaweed-based products faces a number of challenges. This is particularly true for bioplastics and biofuels, which can be characterized by three main aspects. First, the current regulatory framework tends to limit the market entry of new biomaterials; second, consumer awareness and understanding of seaweed-based products is not yet fully developed. Finally, it is difficult to compete with established industries that are already well established in the market (Ayala et al. 2024).

Variability in lifecycle impacts

Seaweed farming is practiced in different ways in different regions, which is a major source of variability in LCA results. In particular, differences in farming methods, the diversity of seaweed species cultivated, and the application of different processing technologies in different regions make consistent interpretation of LCA results difficult (Hasselström and Thomas 2022). In this context, the establishment of a standardized LCA methodology is urgently needed to accurately assess the global potential of seaweed aquaculture. This would increase comparability across regions and enable more reliable assessments of climate change mitigation potential.

Habitat disruption

Large-scale seaweed farms can have a variety of impacts on marine ecosystems. First, the alteration of natural marine habitats can disrupt the habitat of native plants and animals, which in turn can lead to a reduction in biodiversity (Theuerkauf et al. 2022). In particular, dense seaweed farming structures can disrupt the natural migration routes of marine species such as fish, mammals, and seabirds and affect their feeding patterns. In addition, the shading effects of seaweed farms can alter the light environment of aquatic ecosystems (Campbell et al. 2019). These changes can have a significant impact on benthic communities, especially in shallow coastal areas where seagrasses and corals live, which can threaten the health of these ecosystems.

Nutrient competition

Seaweed farming requires dissolved inorganic nutrients such as nitrogen and phosphorus, which have a significant impact on nutrient cycling in marine ecosystems. In nutrient-limited waters, large-scale seaweed farming can result in competition for nutrients with native phytoplankton and other marine organisms, negatively impacting the primary productivity of those ecosystems and overall ecosystem dynamics (Ross et al. 2022). On the other hand, in eutrophicated waters, seaweeds can contribute to improving water quality by absorbing excess nutrients, but this process can rapidly deplete the nutrients in the ecosystem surrounding the farm, disrupting cycling systems (Kotta et al. 2022). Therefore, it is essential to carefully analyze the nutrient status of the waters to determine the appropriate scale for the design and operation of aquaculture farms.

GHG emissions

GHG emissions from the decomposition of seaweeds biomass can be a major factor hindering the effectiveness of seaweed aquaculture in combating climate change. In particular, decomposition under anoxic conditions produces potent greenhouse gases such as methane (CH₄) and nitrous oxide (N₂O), which can occur throughout natural decomposition in the water column, during processing, or during the disposal of seaweed residues (Roth et al. 2023). In addition, halocarbons produced by some seaweed species with high sulfur content contribute to ozone depletion and global warming, further complicating the calculation of net climate benefits from seaweed farming (Keng et al. 2023).

Genetic and ecological risks of introduced species

The cultivation of non-native or genetically modified seaweeds can pose a serious risk to ecosystems. If these species are released into natural ecosystems, they can outcompete native populations and upset the balance of the ecosystem (Campbell et al. 2019). Genetically modified seaweeds, in particular, may have traits that have not arisen through natural selection, giving them an overwhelming advantage over native species. This, in turn, can lead to a reduction in biodiversity in marine ecosystems and, by extension, to changes in overall ecosystem structure, which requires a cautious approach.

Habitat-friendly farm design

The design of seaweed farms is a key factor in the conservation of marine ecosystems, and requires careful consideration to minimize habitat disturbance. For starters, ensuring proper spacing between cultivation lines is crucial to the health of the underwater ecosystem. This is significant because it facilitates light penetration through the water column, ensuring photosynthetic activity in the underlying ecosystem, as well as providing free migration routes for a wide variety of marine species (Flavin et al. 2013, Bak et al. 2020). In addition, the siting of aquaculture farms requires a careful approach to ecosystem conservation. In particular, by avoiding ecologically sensitive areas such as coral reefs, seagrass habitats, and marine protected areas, aquaculture activities can be balanced with the protection of fragile marine ecosystems (Arkema et al. 2024).

Integrated multi-trophic aquaculture

The integrated approach of seaweed farming and other aquaculture systems is of great significance for nutrient cycling in marine ecosystems. In particular, integration with shellfish or fish farming is becoming increasingly important as an effective way to balance nutrient dynamics (Wang et al. 2012, Nederlof et al. 2022). In such integrated aquaculture systems, seaweeds can act as a natural filter to absorb excess nutrients that inevitably occur during fish farming. This could be a solution that goes beyond simply mitigating competition for nutrients and could prevent environmental problems caused by eutrophication in the first place. As a result, this integrated approach can contribute significantly to creating a more sustainable aquaculture environment (Troell et al. 2009, Knoop et al. 2022). Furthermore, the adoption of integrated multi-trophic trophic aquaculture (IMTA) systems goes beyond mere productivity gains and contributes to improving the overall functioning of ecosystems while effectively reducing environmental trade-offs. This can serve as an important model for the future development of marine aquaculture.

Monitoring and regulation of nutrient uptake

The operation of seaweed farms that takes into account the availability and cycling of nutrients is crucial for the health of marine ecosystems. This requires a systematic assessment that takes into account the characteristics of each site to set appropriate thresholds for the nutrient carrying capacity of the waters in question (Roleda and Hurd 2019). This scientific approach plays a key role in preventing excessive consumption of nutrients that can occur during seaweed framing and preserving the natural nutrient cycling of local ecosystems (Chopin et al. 2024). Furthermore, given the dynamic nature of the marine environment, it is essential to establish adaptive management schemes that can flexibly respond to seasonal fluctuations and changes in nutrient concentrations based on regional characteristics.

Management of GHG emissions

The management of seaweed residues is a critical factor in reducing GHG emissions. In particular, there is an urgent need to develop appropriate treatment and processing methods to prevent degradation under anoxic conditions (Abomohra et al. 2022). In this regard, biochar production is gaining attention as an innovative utilization of waste biomass. Biochar is of great significance because it can effectively reduce methane and nitrous oxide emissions while enhancing carbon storage capacity (Lian et al. 2023). In addition, to address the issue of halocarbon emissions, research is actively underway to select low-emitting seaweed species and develop optimized cultivation methods (Leedham et al. 2013, Keng et al. 2023).

Preventing the spread of invasive species

In terms of invasive species management, seaweed farming requires a careful approach to prevent ecosystem disturbance. First and foremost, it is important to select and use native seaweed species or species with proven compatibility with local ecosystems to avoid risks from potential invasive species (Chopin et al. 2024). In addition, more stringent biosecurity measures are required for genetically modified seaweeds, and any consideration of introducing a non-native species should be preceded by a systematic environmental impact assessment to closely examine its potential impact on the ecosystem (Ross et al. 2023).

Marine spatial planning and regulation

A holistic approach to marine spatial planning, including seaweed farming, is essential for effective marine spatial planning. This goes beyond simply selecting the location of aquaculture sites and implies systematic planning that takes into account the interactions and potential conflicts between different marine activities (Lester et al. 2018). Sustainable utilization of marine resources requires balancing the needs of different stakeholders and requires systematic protection of sensitive areas to preserve ecosystems (Bell et al. 2020). To realize this, clear zoning regulations must be established and compliance with environmental standards must be strictly managed through continuous monitoring.

Geographic and environmental advantages

The coastal regions of East Asia, particularly Korea, Japan, and China, possess unique geographical advantages for seaweed farming. These regions benefit from nutrient-rich upwelling currents and temperate climate, and have established themselves as optimal locations for large-scale seaweed production based on aquaculture infrastructure built over decades (Hwang and Park 2020).

Among these, Korea provides ideal natural conditions for seaweed farming with shallow and offshore areas developed along its approximately 15,000 km coastline. In particular, the rias coast of the West and South Seas features well-developed inlets, and its geographical characteristics of shallow depths and large tidal ranges enable the application of various cultivation methods (Hwang et al. 2022). Additionally, the seasonal upwelling phenomenon along the East Sea coast supplies nutrients from deep waters to the surface, promoting seaweed photosynthesis, which influences the carbon dioxide concentration in surrounding seawater and the carbon dioxide exchange between atmosphere and ocean (Kim et al. 2022). These comprehensive environmental conditions provide Korea with optimal conditions for scaling up seaweed farming as a CDR strategy.

Policy frameworks supporting seaweed farming

Seaweed farming is gaining attention as a new strategic option for South Korea’s climate change response. In particular, the 2030 National Greenhouse Gas Reduction Goals (NDCs) and the 2050 Carbon Neutrality Strategy emphasize the importance of blue carbon ecosystems, including seaweeds, in achieving GHG reduction targets (United Nations Framework Convention on Climate Change 2020). Building on this policy framework, the government is providing practical support for the expansion of seaweed farming and the development of its carbon sequestration potential through the Marine Carbon Sequestration Program (Ministry of Oceans and Fisheries 2021), which is leading to innovation in seaweed farming technologies and products through organic collaboration between government, academia, and industry.

Established seaweed industry

South Korea’s seaweed aquaculture industry forms the core of the country’s fisheries industry in terms of production and diversity. From 2018 to 2022, annual cultured seaweed production has remained stable at 1.7 to 1.9 million tons (fresh weight), with Undaria pinnatifida, Saccharina japonica, and Pyropia spp. comprising the main producers at 500,000 to 600,000 tons per year each, and Hizikia fusiforme, Ulva spp., and Codium fragile comprising the secondary producers (KOSIS 2024). This balanced production structure shows the stability and sustainable growth potential of the domestic seaweed farming industry.

The core of seaweed farming technology, the floating longline system, utilizes buoys and ropes on the sea surface to cultivate seaweeds vertically and horizontally. The system increases productivity through efficient utilization of underwater space, minimizes seafloor ecosystem impacts, and provides optimal growing conditions through water depth control (Hwang and Park 2020). This contributes to achieving both ecosystem conservation and economic productivity.

Technological innovations

Ongoing research and development (R&D) is exploring the potential of seaweed for various applications. In particular, large-scale production technologies are being actively developed for various fields such as food, feed, fertilizer, industrial raw materials, and nutraceuticals (Lee et al. 2022, Mihindukulasooriya et al. 2022, Nagahawatta et al. 2023, Kang et al. 2023), laying the foundation for the sustainable development of the seaweeds industry.

In addition, innovative advances in nearshore aquaculture technology are being made. The introduction of automated harvesting systems and multi-trophic level aquaculture facilities has enabled the cultivation of seaweeds at deeper depths, effectively addressing the issue of competition for coastal space (Park et al. 2018, Hwang and Park 2020). In addition, the integration of advanced data-driven tools such as remote sensing and machine learning has enabled real-time monitoring of seaweed farms, raising the overall operational efficiency and environmental stewardship to the next level (Kim et al. 2024).

Carbon sequestration potential

South Korea’s seaweed farming industry currently covers about 23,000 hectares (230 km²) nationwide and produces about 276,000 tons of organic carbon per year. This production corresponds to a net primary production (NPP) of about 1,200 g C m⁻² y⁻¹, which is almost three times higher than the average NPP of natural seaweed communities reported by Krause-Jensen and Duarte (2016) (420 g C m⁻² y⁻¹).

In terms of carbon sequestration, if the average carbon sequestration rate of 11% for wild seaweed communities is applied to domestic seaweed aquaculture production, it can be estimated that about 30,360 tons of carbon is sequestered, equivalent to about 111,300 tons of CO₂ per year. However, this amount of CO₂ removed is influenced by a variety of factors, including farming environment, harvesting methods, ocean currents, and environmental conditions. Notably, it represents only 0.04% of South Korea’s 2030 national GHG reduction target of 291 million tons of CO₂, highlighting the limited direct impact of seaweed aquaculture on overall emissions reductions at present. While it is possible to increase this contribution somewhat by expanding aquaculture acreage and improving containment techniques, the resulting gains are likely to remain marginal compared to national and international climate goals.

Challenges

The main challenges facing the seaweed farming industry in South Korea are: First, there is increasing competition between fishing, tourism, and industrial activities for space in coastal areas. This makes it difficult to secure new space for the expansion of seaweed farming, and requires balanced coordination among various stakeholders. Second, there is the issue of coastal water quality management. Runoff from agricultural activities and wastewater inflows from urban areas are causing eutrophication in some coastal areas, which hinders the normal growth and nutrient uptake of seaweeds. Third, from an economic perspective, scaling up seaweed farming involves significant costs, particularly in building the infrastructure to operate offshore farms and process the harvest, and the uncertainty of the market for seaweed-derived products makes these investment decisions even more challenging. Finally, from an environmental perspective, the impact of large-scale seaweed farming on coastal ecosystems needs to be considered. In particularly sensitive coastal ecosystems, habitat alteration and disruption of nutrient balances can occur, which can negatively impact the health of marine ecosystems in the long term.

Future potential

The future of the seaweed aquaculture industry can realize its potential through a number of innovative development directions. The development and expansion of nearshore aquaculture systems offers an opportunity to effectively utilize unutilized marine space while addressing space utilization issues in coastal areas. This would be a practical way to scale up aquaculture while minimizing conflicts with existing coastal activities.

The establishment of a systematic MRV framework for seaweed carbon sequestration is another important way forward. Such a framework would enable integration with carbon crediting schemes, which would contribute to ensuring that the seaweed farming industry has the economic incentive to attract new investments and scale up operations.

Diversification of seaweed-derived products is also a key factor in increasing the economic sustainability of the industry. Expanding into different product lines, such as biodegradable plastics, livestock feed, and biofuels, can improve the profitability of the industry while contributing to the fight against climate change.

With its advanced aquaculture infrastructure and policy support, South Korea has the potential to take a leading position in blue carbon research. It has sufficient capacity to lead global research, especially in key research areas such as stability of DOC, burial efficiency of particulate organic carbon, and LCA.

Research gap

DOC released by seaweeds plays a key role in the ocean’s carbon cycle. However, only a limited fraction of this DOC is actually converted to RDOC, which contributes to long-term carbon sequestration (Zhang et al. 2023). Studies to date have not fully elucidated the environmental factors and biochemical mechanisms involved in this conversion process, which is an important limitation in accurately assessing and optimizing the efficiency of seaweed-based carbon sequestration.

Future directions

To understand the conversion of DOC to RDOC in seaweeds, systematic field experiments under different environmental conditions are essential. By quantitatively analyzing the effects of environmental factors such as temperature, nutrient availability, and microbial activity on the conversion rate, a deeper understanding of the mechanisms of RDOC production can be gained. Based on these experimental data, it will be possible to develop biogeochemical models that predict RDOC production rates based on seaweed species-specific characteristics and cultivation methods. In particular, by studying the impact of specialized compounds, such as complex polysaccharides found only in certain macroalgae (seaweeds), on RDOC formation, it is expected that more efficient carbon sequestration strategies can be developed.

Research gap

The efficiency of POC burial in marine sediments is determined by a complex interplay of many environmental factors. Key influencing factors include the rate of sediment accumulation, oxygen concentration in seawater, and bioturbation from the activities of seafloor organisms, all of which exhibit significant spatial and temporal variability (Dolliver and O’Connor 2022). Current POC burial efficiency estimation methods do not fully account for these complex interactions, limiting their ability to accurately predict long-term carbon sequestration potential. This poses a significant challenge for assessing and optimizing the effectiveness of seaweed-based carbon sequestration strategies.

Future directions

Improving the burial efficiency of POC requires a systematic research approach. A first step is to utilize advanced sediment coring techniques to precisely measure POC deposition and burial rates in seaweed farming areas. The data collected can then be used to analyze the impact of various characteristics of the sediment, such as particle size and organic matter content, on POC stabilization. Furthermore, to apply these findings to actual aquaculture operations, strategies should be developed to maximize POC burial efficiency, such as selecting areas with high sediment accumulation rates and developing optimized aquaculture methods.

MRV challenges

Global framework integration

Offshore seaweed farming

Integrated multi-trophic aquaculture

Seaweed genetics and bioengineering

Carbon sequestration mechanisms

The carbon sequestration capacity of seaweeds is determined by biomass production and species-specific carbon content. While the annual carbon sequestration potential of seaweeds is estimated at 61–268 Tg C (Krause-Jensen and Duarte 2016), it remains unclear whether this will result in CDR lasting more than 100 years. Understanding carbon sequestration requires distinguishing between several key terms: carbon sequestration means long-term CO₂ removal over 100 years; carbon fixation refers to initial CO₂ uptake through photosynthesis; carbon assimilation describes CO₂ conversion into seaweed biomass; carbon storage indicates short-term retention; and carbon burial denotes permanent removal in sediment. Since researchers often use these terms interchangeably without clear distinction, calculating actual CO₂ removal and long-term storage becomes challenging.

Seaweed farming employs three main pathways for carbon sequestration. First, biomass storage provides short-term carbon removal, though its long-term effectiveness depends on post-harvest processing methods like biochar production or integration into durable materials (Pessarrodona et al. 2024). Second, DOC—especially RDOC—shows promise as a long-term sequestration mechanism, though questions remain about its stability and production rates (Zhang et al. 2023). Third, POC burial offers a stable storage pathway in anaerobic sediments, with its efficiency largely determined by local sedimentation rates and bioturbation levels (Erlania et al. 2023).

LCA and indirect benefits

Seaweed-based products can contribute to climate change mitigation by replacing carbon-intensive products. Among these products, bioplastics, biochar, and livestock feed additives are gaining traction because of their significant carbon reduction potential. Specifically, seaweed bioplastics can reduce lifecycle GHG emissions by up to 50% compared to conventional petroleum-based plastics (Lim et al. 2021), and livestock feed additives have been shown to reduce methane emissions from livestock by up to 80% (Machado et al. 2016). However, a notable challenge is that the production and processing of these seaweed-based products requires significant energy consumption, so efforts to incorporate renewable energy into the production process and continuously improve process efficiency are essential to maximize their climate change mitigation potential.

Regional case study: South Korea

South Korea has secured global competitiveness in seaweed farming based on its advanced aquaculture infrastructure and government support. By efficiently utilizing coastal space and systematically managing nutrients, the country has established a sustainable production base and is now consolidating its position as a major producer in the global market. What is particularly noteworthy is that the biomass losses from seaweed farming are buried in sediments for long-term storage. This process of carbon burial provides an important mechanism for long-term sequestration of atmospheric carbon by accumulating organic carbon from seaweeds in sediments, and is recognized as one of the most reliable methods of carbon sequestration in the ocean, with minimal re-emissions. Furthermore, through innovations in offshore aquaculture technology and the introduction of IMTA systems, the Korean seaweed industry has the potential to develop in a more sustainable direction.

Environmental and ecological trade-offs

Large-scale seaweed farming can have a variety of environmental impacts on marine ecosystems. In particular, ecological risks such as habitat destruction, competition for nutrients, and methane emissions from biomass decomposition are major concerns (Campbell et al. 2019). To minimize these environmental impacts, sustainable aquaculture farm design and appropriate siting are essential and must be considered in an integrated manner with broader marine spatial planning initiatives. In this context, innovative mitigation strategies such as IMTA and nearshore aquaculture are gaining traction. These strategies can not only effectively reduce environmental risks, but also provide the added benefits of increased productivity and enhanced ecosystem functioning. IMTA systems, in particular, integrate organisms of different trophic levels, which can help to promote nutrient cycling and maintain ecosystem balance.

Research gaps and future directions

A number of scientific uncertainties need to be addressed for the sustainable development of seaweed farming systems. In particular, the long-term stability of RDOC, the burial efficiency of POC, and the net carbon balance of the entire system need to be further studied. Addressing these research challenges will be preceded by the development of standardized MRV systems, which will ultimately play a key role in the successful integration of seaweed farming into carbon markets and global climate frameworks (Cadman and Hales 2022). Meanwhile, advances in nearshore aquaculture technologies and innovative approaches such as genetic optimization offer new possibilities to address these challenges and improve the scalability and efficiency of seaweed farming.

Strengths

Seaweed farming is noteworthy for a number of reasons. First, seaweed farming is a highly scalable solution, as it does not require freshwater or arable land, minimizing competition with terrestrial resources. In addition, seaweed farming is not limited to carbon sequestration alone, but offers a range of additional benefits such as habitat restoration, nutrient pollution mitigation, and sustainable food and feedstock production. Furthermore, seaweed farming can simultaneously address both mitigation and adaptation to climate change, effectively contributing to the achievement of international climate goals represented by the Paris Agreement and the Sustainable Development Goals.

Challenges

One of the biggest challenges to seaweed farming is the uncertainty of its long-term carbon sequestration effectiveness. In particular, variability in the production of RDOC, burial efficiency of POC, and carbon retention in biomass make it difficult to accurately predict the long-term potential for carbon sequestration through seaweed farming. In addition, large-scale seaweed farming can have a significant impact on marine ecosystems, which, without proper management, can lead to disturbance of natural habitats and imbalances in nutrient cycling. In addition to these ecological concerns, there are also economic and technical barriers to the expansion of the seaweeds industry. High upfront investment costs for aquaculture facilities, limited market structure, and energy-intensive processing processes are key factors that make commercialization and market penetration of seaweeds-based products difficult.

Opportunities for improvement

Technological innovation in seaweed farming will be a key driver for sustainable development. In particular, the introduction of automated offshore aquaculture systems can dramatically improve productivity, while the use of biogeochemical modeling tools can enable accurate monitoring of carbon sequestration processes. In addition to these technological advances, expanding the range of uses for seaweeds, such as biofuels and building materials, will increase their economic viability while also having a positive impact on climate change mitigation. To realize these advances, it is essential that governments, academia, and industry work together to drive innovation and create the policy framework for the sustainable expansion of seaweed farming.

Comparison with other CDR strategies

Seaweed farming is complementary to other CDR approaches. In particular, compared to afforestation and BECCS, seaweed farming offers a unique advantage in that it utilizes the marine environment without using terrestrial resources. Moreover, unlike other CDR approaches, such as marine fertilization or direct air capture, which focus on a single objective, seaweed farming offers the additional benefits of enhancing food security and increasing marine ecosystem diversity in addition to the primary goal of carbon sequestration. This multifaceted approach makes seaweed farming a more socially and ecologically attractive climate change response strategy.