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Summary

Seaweed farming

Seaweed or kelp farming involves cultivating and harvesting seaweed, ranging from simply collecting seaweed from natural beds to fully managing its entire life cycle. In recent years, seaweed farming has emerged as a promising climate change mitigation and adaptation strategy due to its capacity to sequester carbon, enhance marine biodiversity, and support coastal resilience[1]. For instance, estimates say that approximately 4–44 teragrams of seaweed-derived carbon could be sequestered annually for 100 years as a result of the organic carbon exported from seaweed forests entering the deep ocean[2]. Seaweed enhances marine biodiversity by providing habitats and improving water quality through nutrient absorption, contributing to healthier marine ecosystems[3]. Economically, seaweed farming supports coastal communities by creating sustainable livelihoods and reducing pressure on overexploited fisheries, aligning with the goals of the blue economy to balance economic growth with environmental health[4]. As coastal regions face increasing climate threats, seaweed farming offers adaptive benefits by protecting shorelines from erosion and enhancing food security[5]. This multifaceted approach supports several Sustainable Development Goals, including Zero Hunger, Decent Work and Economic Growth, Climate Action, Life Below Water, and Life on Land.

Seaweed and Climate Change: Historical Insights into Mitigation and Adaptation Efforts

The Ocean’s Role in Climate Mitigation and Adaptation

Climate change is a global challenge driven by human activities such as fossil fuel combustion, deforestation, and industrial processes, increasing greenhouse gas (GHG) concentrations. This results in rising global temperatures, sea level rise, extreme weather events, and disruptions to ecosystems. Oceans play a critical role in climate regulation by absorbing vast amounts of heat and CO₂. Marine ecosystems, particularly those created by seaweed, contribute to carbon storage and sequestration, helping offset anthropogenic emissions. Seaweed is a fast-growing marine algae that absorbs large amounts of atmospheric CO2 through photosynthesis, reducing atmospheric carbon levels and ocean acidification[6].

History of Seaweed farming

Seaweed farming began to gain prominence in the early 20th century, particularly in Japan, where systematic cultivation of species such as Laminaria was developed to support food and the extraction of phycocolloid production. Phycocolloids are gel-like substances from seaweed that are major economic driver due to their natural and sustainable properties and wide industrial use. From the1950s to the 1990s, there was an increased scientific research into the nutritional and health benefits of seaweed as a source of nutrients, minerals, and vitamins, particularly iodine. Since the19190s, increased interest in sustainable practices has led to a resurgence in seaweed farming across the globe, particularly as awareness of climate change has grown [7]. Today, it is increasingly recognized not only for its ecological benefits, such as carbon sequestration and habitat restoration, ut also for its potential role in building more resilient and sustainable food systems.

Overview of commonly farmed seaweed species and farming techniques
The mainstay of the local economy - seaweed farming.

Seaweed farming includes thousands of species, leading to different techniques adapted to local needs and environments. Key species like Kappaphycus, Gracilaria, Laminaria, and Ulva are farmed for food, cosmetics, and phycocolloids [8]. Phycolloids are a biodegradable alternative to synthetic chemicals in food, packaging, and medicine. Traditional methods include stake and rope lines, recognized as common cultivation techniques adapted to local environmental conditions. Traditional methods have been developed and refined over generations to suit the specific environmental conditions of the site, including water depth, flow rates, and nutrient availability. Farmers typically adjust their methods based on these factors, enhancing their local knowledge and the sustainability of the cultivation practices. Seaweed farming is often deeply rooted in local cultures and traditions prevalent in Southeast Asia, providing not just economic benefits but also social and cultural identity. Newer techniques like offshore longlines and vertical farms are emerging in Europe and North America. Offshore longlines can be extended over large areas, allowing for greater biomass production compared to traditional coastal methods. Furthermore, these setups can enhance biodiversity by providing habitats for marine life[9].

Current Status and Future Prospects

The global seaweed industry was valued at approximately $6.4 billion in 2014 and has seen exponential growth over the last 50 years, accounting for about 49% of total mariculture production, which stood at 27.3 million tonnes in 2014. In 2014, China produced 12.8 million tonnes of seaweed, representing 54% of global production, followed by Indonesia at 6.5 million tonnes (27.4%). An ecosystem-management approach is being developed for marine spatial planning to address increasing demands from various sectors, promoting cooperation through regional policies that allow for sustainable growth while avoiding conflicts. The industry is projected to continue expanding as demand grows, particularly for contaminant-free seaweed for food and pharmaceuticals.[10]

The potential of seaweed farming to slow down climate change

Seaweed Farming as a Tool to Reduce Climate Change - Ocean Carbon Sink

As carbon emissions continue to rise, seaweed farming has proven to be a hopeful climate change mitigation strategy. As seaweed grows, it releases carbon that has been buried in sediments or exported to the deep sea. In other words, seaweed generates far more organic matter through photosynthesis than is consumed by respiration in the ecosystem. Therefore, seaweed is considered a CO2 sink and is responsible for lots of the CO2 captured in marine vegetated habitats[11]. By consuming CO2, seaweed farms are able to directly offset CO2 produced by the variety of human activities and therefore directly mitigate the gasses that cause global warming. Seaweed farming not only helps sequester carbon in the atmosphere but also helps in the agricultural sector through synthetic fertilizer substitutes. Fertilizers are commonly used in farming practices to boost the growth and production of crops, and synthetic fertilizers are most commonly used. Cattle are common livestock, however, their methane output is considered a greenhouse gas, thus contributing to global warming. However, as seaweed is grown and harvested, it can be processed in a way that it can be incorporated into cattle feed. Through a shift in their diet, seaweed has been proven to reduce cattle methane emissions. In turn, cattle waste can be utilized as natural fertilizer, therefore substituting synthetic fertilizers, whose processing can produce large sums of CO2 emissions[12].

Seaweed Farming as a Tool to Reduce Climate Change - Reducing Ocean Acidification

As CO2 emissions continue to rise, the impact on ocean pH and therefore all marine life is at risk via ocean acidification. Ocean acidification means that the ocean pH decreases as a result of an increase of CO2 diffusing from the atmosphere. As increased CO2 emissions reduce ocean pH, many ocean cycles and processes are directly impacted. A low pH causes the lowering of calcium carbonate saturation states. Calcium carbonate is used by a variety of shell-forming marine organisms- such as corals, mollusks, and crustaceans- to create their shells of protection[13]. With lowering pH and thus the lowering of calcium carbonate saturation states, marine organisms will not be able to form their shells and therefore will be more susceptible to predators. Seaweed farming can be one solution to tackle the ever-present and alarming consequence of ocean acidification. As seaweed grows, it colonizes more territory, all the while sucking diffused Co2 from the water through photosynthesis. As seaweed absorbs CO2 within the ocean, it lowers its concentration and helps return the pH to neutral levels, therefore protecting shell-forming marine organisms [14]


Social Benefits of Seaweed Farming for Climate Change Mitigation

Seaweed farming positively impacts the communities in which it is practiced. Algae aquaculture is commonly carried out by community members and is attractive to farmers in rural coastal communities due to its low cost and high capital. Farming techniques are not technically demanding and labour input is relatively low, therefore allowing seaweed farming to be a side business for some extra cash. In addition to direct financial benefits, seaweed farming also contributes to human and social capital within seaweed farming households and communities[15]. Furthermore, seaweed farming has proven to be an opportunity for women to enter the workforce in different geographic locations. By creating an opportunity for women to contribute to their household income, and therefore experience a higher quality of life, seaweed farming has proven to be an important ecological and economic mitigation strategy for dealing with climate change[16].

Challenges and Limitations

As an ocean-based carbon dioxide remover, seaweed farming offers high hopes for climate change mitigation. Indeed, the carbon capture capacities of seaweed could be useful in reaching net-zero CO2 emissions (i.e., seaweed farming could help in reducing greenhouse gas emissions to a level that can be absorbed by the environment).[17][18] However, biophysical and economic factors raise limitations in reaching that objective.[18]

Firstly, according to climate scenarios, from the year in which CO2 emissions reach net zero, more than 1 gigaton of carbon would need to be removed annually from the atmosphere to keep global warming beneath 1.5°C or 2°C.[18] However, in 2018, the harvest of seaweed for food amounted to a carbon removal capacity of roughly 1 million tons of carbon per year, which is a thousand times less than what would need to be produced to reach net zero through seaweed farming.[18] Thus, seaweed farming would have to expand significantly to contribute effectively to the reduction of CO2 in the atmosphere.

Environmental and economic costs of this necessary expansion remain to be estimated, creating further uncertainties and limiting factors in this search for solutions to mitigate climate change.[18] Nutrient availability, for that matter, is key to the environmental and economic success of large-scale seaweed farming. Direct competition between phytoplankton and seaweed for nutrient intake drastically reduces the possibility of expanding seaweed farms.[18] On the one hand, this expansion could be harmful to phytoplankton productivity, which is essential to the balance of marine systems.[18] On the other hand, limited nutrient availability restricts the production of seaweed, thus limiting the economic success of large-scale farming.[18]

Overall, the possibility of expanding seaweed farming to a scale significant enough to mitigate global warming relies solely on whether methods will be found to enhance nutrient availability in the future, which is yet to be observed.

Case Studies

Although seagrass, mangroves, and tidal marshes are included in the Intergovernmental Panel on Climate Change Greenhouse gas accounting guidelines, seaweed forests are yet to be formally recognized as blue carbon ecosystems.[19] However, various examples around the world demonstrate the emergence of seaweed forests as the main contributors to long-term carbon storage.[20]

In Canada, for example, initiatives are developed to increase the standing stock of kelp-associated carbon and conserve kelp forests which could act as natural climate solutions.[20]

In Norway, policymakers have been called to action to increase seaweed forest conservation efforts. Hosting the second largest seaweed biomass in Europe, Norway constitutes a promising ground for climate mitigation through seaweed farming.[19]

In Australia, kelp forests account for over 30% of the total blue carbon stored and sequestered around the Australian continent, contributing approximately 3% of the global total of blue carbon.[21]

These are not isolated examples, and researchers are working towards the recognition of the potential of seaweed farming for effective carbon storage and sequestration. The resulting research outcomes could then be used to increase the inclusion of these organisms into global blue carbon budgets and offset schemes.[21]

The potential of seaweed farming for climate change adaptation

Bioeconomy applications - Seaweed as a biobased adaptation solution

Seaweed has climate change mitigation co-benefits such as being used as a carbon sink and providing ecosystem services, but it can also be used as a bioproduct to support efforts in changing our fossil-fueled-based economy to a more sustainable bioeconomy. Growing seaweed is faster, more space-efficient, and does not require the use of fresh water or the addition of fertilizer. Furthermore, seaweed does not compete for land area. On the contrary, seaweed can be grown in exactly the area we have the most of: the sea.[22] Seaweed could answer the needs of our growing population while adapting to current climatic conditions.

Biofuels

Transportation is one of the largest contributors to greenhouse gas emissions according to the EPA[23] and it accounted for the largest portion (28%) of total U.S GHG emissions in 2022. With a growing population, our demand for transportation will increase and seaweed can help us meet our long-term energy demands due to its promising biomass output, cost-effective culture, and mass farming capabilities[24]. Seaweed is capable of growing in non-arable land with high biomass productivity, which results in a high yield of energy-rich compounds such as lipids and carbohydrates, the substrates for bioethanol and biodiesel respectively. This makes them a promising substitute option for traditional fossil fuels. Additionally, their adaptability for direct use in existing infrastructures makes them more cost-effective and faster to implement[25] They also have potential for mass farming, as unlike terrestrial crops that could be grown for biofuel, seaweed does not compete with agricultural lands for its farming, and avoids competition with food crops[24]. Some examples of seaweed use for biofuel can be seen globally. For example, in Alaska, a research team found a way to take the fish waste and combine it with kelp to make a biocrude, low-grade fuel that could cost roughly half of a gallon of fuel that would be flown in. The economical cultivation and large-scale farming potential amongst other factors make seaweed a promising substitute for fossil fuels, helping us adapt to current climatic conditions.

Bioplastics

Seaweed can also replace fossil products besides fuel, including plastics, cosmetics, and textiles. Plastics are highly toxic to humans and animals because of their chemical composition and indefinite bioaccumulation in the environment. To meet the plastic demand of our population, we need to adapt and find a more sustainable alternative which can be found in seaweed. The emergence of bioplastics offers innovative sustainable options due to their ease of degradability, with lower negative environmental impacts, making them a potential solution to the plastic waste problem[24]. Seaweed could once again offer a sustainable, less energy-demanding, and nature-degrading option to fulfill our demand while adapting to current environmental conditions.  

Limitations

Seaweed has been explored as a promising alternative to fossil fuels, but it faces several limitations in order to make it a large-scale biofuel source. One major limitation is its economic viability as cultivation solely for biofuels is not profitable at this time[24] and cannot compete with global markets. However, dedicated large-scale seaweed farming is needed to attain and maintain a complete reliance on biofuel[26]. The substitution of fossil fuels for seaweed is therefore currently unfeasible.

Another drawback to the large-scale implementation of seaweed use is the lack of understanding of seaweed’s potential in more diverse areas as well as the absence of comprehensive policy linked to national and international strategies making the global implementation of seaweed unfeasible[22].  Limitations also arise from ecological concerns and ethical considerations discussed in the next section. These barriers must be addressed before seaweed can serve as a viable alternative to fossil fuels at an industrial global scale.  

Ethical Considerations

Seaweed farming's environmental effects are considered insignificant in comparison to other forms of aquaculture and mariculture (i.e., fish and bivalve farming). [27] However, the introduction of invasive species in the wild can actively threaten genetic biodiversity as well as the surrounding ecosystems.[28] Moreover, concerns have been raised about the entanglement of marine mammals in seaweed farms (kelp farms more specifically).[29] At last, surrounding ecosystems may go under change through light reduction imposed by the growing presence of macroalgae.[29]

Marine biologists, such as Alexandra Morton, or ocean conservation activists such as Captain Paul Watson have warned against the potential negative impacts of large-scale seaweed farming.[30] This is in part due to the negative impact of fish farms on the marine environment.[30] Fish farms were historically met with the same enthusiasm as seaweed farming, and are now present active threats to their surrounding environments for being so poorly managed, explaining the skepticism from some scientists and environmentalists.[30]

All in all, whether a seaweed farm will have a negative impact on the environment or not depends entirely on the size of the farm, and on how it is managed. Given that there are currently no regulations on farm size, native seed collection, or responsibility in the industry, decision-makers should ensure the development of a strong legal framework to ensure that this growing industry remains sustainable and beneficial to the natural environment.[30]

Although Seaweed farming is seen as a promising contributor to sustainable development, particularly in the Blue Economy context, its social and ecological benefits are often under-researched and context-dependent.[31] While some positive impacts are consistent (e.g., improved water quality and enhanced coastal livelihoods), other claimed benefits lack empirical support and vary across regions.[31] As seaweed farming expands, attention must be given to the potential social and economic risks, ensuring that the industry grows in both an equitable and sustainable way.

Conclusion

Seaweed farming is key to environmental sustainability, climate change mitigation and adaptation, and socio-economic development. Through its historical roots in traditional aquaculture practices and its emerging importance in global climate strategies, seaweed farming offers a new promising approach to the pressing issue of climate change.

Its capacities to naturally sink carbon, reduce ocean acidification, enhance ecosystem health, and provide sustainable livelihoods are non-negligible in the search for solutions to adapt to climate change. Furthermore, its bioeconomic potential stands out, offering alternatives to fossil fuels and industrial pollutants through the development of biofuels.

However, the benefits of seaweed farming remain restricted, and challenges such as scalability limits, nutrient competition, and economic, ecological, and political uncertainty are yet to be overcome.

There is a crucial need for research expansion on the topic if seaweed farming is to be used increasingly for climate change adaptation and mitigation. Especially, decision-makers and researchers should work collaboratively to ensure that seaweed aquaculture evolves responsibly and equitably, establishing a truly sustainable and just future.

References

  1. ↑ Duarte, C. M.; Wu, J.; Xiao, X.; Bruhn, A.; Krause-Jensen, D. (2017). "an seaweed farming play a role in climate change mitigation and adaptation?". Frontiers in Marine Science. 4: 100.
  2. ↑ Filbee-Dexter, K.; Pessarrodona, A.; Pedersen, M. F.; Wernberg, T.; Duarte, C. M. (2024). "Carbon export from seaweed forests to deep ocean sinks". Nature Geoscience. 17(6): 552–559.
  3. ↑ Gentry, R. R.; Alleway, H. K.; Bishop, M. J.; Gillies, C. L.; Waters, T. (2019). "Exploring the potential for marine aquaculture to contribute to ecosystem services". Reviews in Aquaculture. 12: 1090–1102.
  4. ↑ Campbell, I.; Macleod, A.; Sahlmann, C.; Neves, L.; Funderud, J.; Øverland, M.; Hughes, A. D.; Stanley, M. (2019). "The environmental risks associated with the development of seaweed farming in Europe - prioritizing key knowledge gaps". Frontiers in Marine Science. 6: 107.
  5. ↑ Froehlich, H. E.; Afflerbach, J. C.; Frazier, M.; Halpern, B. S. (2019). "Blue growth potential to mitigate climate change through seaweed offsetting". Current Biology. 29(18): 3087–3093.
  6. ↑ Chung, I. K.; Beardall, J.; Mehta, S.; Sahoo, D.; Stojkovic, S. (2010). [DOI 10.1007/s10811-010-9604-9 "Using marine macroalgae for carbon sequestration: A critical appraisal"] Check |url= value (help). Journal of Applied Phycology. 23(5): 877–886.
  7. ↑ Cadée, G. C. (1992). "Review of the book Seaweed resources in Europe: Uses and potential, by M. D. Guiry & G. Blunden (Eds.)". Aquaculture. 107(4): 395–396.
  8. ↑ Ganesan, P; Kumar, C; Bhaskar, N (2008). "Antioxidant properties of methanol extract and its solvent fractions obtained from selected Indian red seaweeds". Bioresource Technology. 99: 2717–2723.
  9. ↑ Waqas, M; Hashemi, F; Mogensen, L; Knudsen, M. "Emerging seaweed cultivation techniques: Offshore longlines and vertical farms as sustainable solutions in Europe and North America". Sustainable Production and Consumption. 48: 123–142.
  10. ↑ Cottier, E; Nagabhatla, N; Campbell, M; Chopin, T; Hewitt, G; Kim, G; Huo, Y; Jiang, Z; Kema, G (2016). "Safeguarding the future of the global seaweed aquaculture industry".
  11. ↑ Duarte, Carlos M.; Wu, Jiaping; Xiao, Xu; Bruhn, Annette; Krause-Jensen, Dorte (2017). "Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation?". Frontiers in Marine Science. 4.
  12. ↑ Bullen, Cameron D.; Driscoll, John; Burt, Jenn; Stephens, Tiffany; Margot, Hessing-Lewis; Gregr, Edward J. (2024-07-01). "The potential climate benefits of seaweed farming in temperate waters". Scientific Reports. 14: 15021.
  13. ↑ Schultz, Jack; Gobler, Dianna L. Berry; Young, Craig S.; Perez, Aleida; Doall, Michael H.; Gobler, Christopher J. (2024). "Ocean acidification significantly alters the trace element content of the kelp, Saccharina latissima". Marine Pollution Bulletin. 202: 116289.
  14. ↑ Chung, Ik Kyo; Sondak, Calvyn F. A.; Beardall, John (2017-10-02). "The future of seaweed aquaculture in a rapidly changing world". European Journal of Phycology. 52: 495–505.
  15. ↑ Rimmer, Michael A; Larson, Silva; Lapong, Imran; Purnomo, Agus Heri; Pong-Masak, Petrus Rani; Swanepoel, Libby; Paul, Nicholas A (2021). "Seaweed aquaculture in Indonesia contributes to social and economic aspects of livelihoods and community wellbeing". Sustainability. 13: 10946.
  16. ↑ Msuya, Flower E.; Hurtado, Anicia Q. (2017-10-02). "The role of women in seaweed aquaculture in the Western Indian Ocean and South-East Asia". European Journal of Phycology. 52: 482–494.
  17. ↑ United Nations (2024). "For a Livable climate: Net-zero Commitments Must Be Backed by Credible Action".
  18. ↑ 18.0 18.1 18.2 18.3 18.4 18.5 18.6 18.7 DeAngelo, J., Saenz, B. T., Arzeno-Soltero, I. B., Frieder, C. A., Long, M. C., Hamman, J., … Davis, S. J (2022). "Economic and biophysical limits to seaweed farming for climate change mitigation. Nature Plants". Nature Plants. 9: 45–57.CS1 maint: multiple names: authors list (link)
  19. ↑ 19.0 19.1 NBFN (2024, May 31). "New research brings us one step closer to making seaweed an "actionable" blue carbon ecosystem". Check date values in: |date= (help)
  20. ↑ 20.0 20.1 Alleway, H., Baum, J., Beck, A., Bullen, C., Burt, J., Carlson, D., & Currie, J. (2023). "COASTAL BLUE CARBON IN CANADA: STATE OF KNOWLEDGE" (PDF).CS1 maint: multiple names: authors list (link)
  21. ↑ 21.0 21.1 Filbee-Dexter, K., & Wernberg, T. (2020). "Substantial Blue Carbon in Overlooked Australian Kelp Forests". Scientific Reports. 10(1).CS1 maint: multiple names: authors list (link)
  22. ↑ 22.0 22.1 Bellona Europa (Mar 6, 2017). "Pros and Cons Seaweed for Biofuel" (PDF).
  23. ↑ United States EPA (18 June 2024). "Fast Facts on Transportation Greenhouse Gas Emissions | US EPA". Environmental Protection Agency.
  24. ↑ 24.0 24.1 24.2 24.3 Yong, Wilson Tha; Thien, Vun Yee; Rupert, Rennielyn; Rodrigues, Kenneth Francis (May 2022). "Seaweed: A potential climate change solution". Renewable and Sustainable Energy Reviews. 159.
  25. ↑ Elshobary, Mostafa E.; El-Shenody, Rania A.; Abomohra, Abd El-Fatah (4 November 2020). "Sequential biofuel production from seaweeds enhances the energy recovery: A case study for biodiesel and bioethanol production". International Journal of Energy Research.
  26. ↑ Marquez, Gian Powell B.; Santiañez, Wilfred John E.; Trono Jr., Gavino C.; de la Rama, Sharon Rose B.; Takeuchi, Hisae; Hasegawa, Tatsuya (2015). "Chapter 16 - Seaweeds: a sustainable fuel source". Seaweed Sustainability: 421–458.
  27. ↑ Visch, W., Kononets, M., Hall, P. O. J., Nylund, G. M., & Pavia, H. (2020). "Environmental impact of kelp (Saccharina latissima) aquaculture". Marine Pollution Bulletin. 155: 110962.CS1 maint: multiple names: authors list (link)
  28. ↑ Marquez, G. P. B., Santiañez, W. J. E., Trono, G. C., de la Rama, S. R. B., Takeuchi, H., & Hasegawa, T. (2015). "Seaweeds: a sustainable fuel source". Seaweed Sustainability: 421–458.CS1 maint: multiple names: authors list (link)
  29. ↑ 29.0 29.1 World Wildlife Fund Website. "Farmed Seaweed | Industries |".
  30. ↑ 30.0 30.1 30.2 30.3 Dressel, H. (2022, September 28). "In seaweed, climate capitalists see green". The Breach. Check date values in: |date= (help)
  31. ↑ 31.0 31.1 Spillias, S., Kelly, R., Cottrell, R. S., O’Brien, K. R., Im, R.-Y., Kim, J. Y., … McDonald-Madden, E. (2023). "The empirical evidence for the social-ecological impacts of seaweed farming". PLOS Sustainability and Transformation. 2(2).CS1 maint: multiple names: authors list (link)


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