Though we live on an undeniably watery planet, the ocean and the seafloor remain largely unexplored.
Last month, I led the inaugural Climate @ Work Employee Training, a new workshop by Project Drawdown designed to help non-sustainability employees understand the role of businesses – and most importantly, their employees – in scaling climate action.
Improving aquaculture involves reducing CO₂ and other GHG emissions during the production of farmed fish and other aquatic animals through better feed efficiency and the decarbonization of on-farm energy use. Advantages include reduced demand for feedstocks produced from both wild capture fisheries and terrestrial sources, which benefits marine and terrestrial ecosystems. Disadvantages include the costs of transitioning to fossil-free energy sources. While these interventions are unlikely to lead to globally meaningful emissions reductions (>0.1 Gt CO₂‑eq/yr ), we consider Improve Aquaculture as “Worthwhile” given the rapid and ongoing expansion of the industry, its potential to replace higher-emission protein sources, and the ecosystem benefits of reducing feedstock demand.
While Improve Aquaculture is unlikely to have a major climate impact, our assessment concludes that it is “Worthwhile” due to its ability to reduce pressure on wild fish stocks and terrestrial biomass, and because efficiency improvements made now are likely to scale into greater climate impact as the sector continues to expand.
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | ? |
GHG emissions from aquaculture can be reduced by increasing the feed conversion efficiency of the cultured animals and decarbonizing on-farm energy use. Aquaculture – farming aquatic animals or plants for food or other purposes – is rapidly growing and now accounts for over half of the global production of aquatic animals, exceeding wild capture fisheries. Over 7% of human-consumed protein is aquaculture-produced. As this sector has grown, it has become increasingly reliant on external feed sources, with the share of non-fed aquaculture (e.g., bivalves that feed from the water column) dropping from nearly 40% in 2000 to 27% in 2022. Improving feed conversion ratios (FCR) – the amount of feed it takes to produce a given amount of biomass – can lower feed demand and reduce CO₂ and other GHG emissions tied to feed production and transport. FCRs can be improved by feed formulations that increase digestibility, genetic or breeding modifications to improve digestive efficiency in the cultured animal, species-specific feed formulations, and optimizing ration size and feeding frequency. At the same time, decarbonizing on-farm energy use can help reduce CO₂ emissions from common equipment, such as aerators and water pumps.
Interventions to improve feed and energy efficiency can reduce CO₂ emissions from aquaculture operations, although the potential achievable climate impact of these actions is currently unlikely to be globally meaningful (>0.1 Gt CO₂‑eq/yr ). Total annual emissions from aquaculture were estimated to be 0.26 Gt CO₂‑eq/yr in 2017, with nearly 60% of that attributed to feed production. Improving FCR is both plausible and effective, since it directly reduces the amount of food needed to cultivate fish and other species, thereby lowering emissions tied to feed production and transport. Between 1995 and 2007, improvements in FCR have ranged between 5 to 15% for a variety of species, including shrimp, salmon, carp, and tilapia.
Decarbonizing on-farm energy use can reduce equipment-related emissions, particularly in intensive systems that use energy for automated feeding systems, water temperature control, and circulation and aeration systems. In general, the potential impact of decarbonizing varies widely because on-farm energy use differs significantly across species and production systems. For instance, shrimp and prawn farming use nearly 20,000 MJ/t of live weight (LW), with over 75% from electricity, while bivalve production uses around 3,000 MJ/t of LW supplied largely by diesel.
Improving feed efficiency in aquaculture reduces demand for captured wild fish used in feed, reducing pressure on overfished stocks. It also lowers reliance on terrestrial biomass, such as soy, wheat, and rice, which come with additional land-use and emission costs. More efficient feeding can help reduce nutrient pollution, which can be responsible for high methane and nitrous oxide fluxes in some inland aquaculture systems. At the same time, decarbonizing on-farm energy use might ultimately lead to lower long-term operating costs and improved energy reliability.
There are relatively few drawbacks associated with improving aquaculture. In the case of decarbonizing on-farm energy use, upfront costs could be high. For instance, installing solar panels or upgrading pumps can be financially challenging for small-scale operations. Energy use on farms can also vary throughout the day and night, which might not always align with renewable energy sources, like solar, without storage.
Badiola, M., Basurko, O. C., Piedrahita, R., Hundley, P., & Mendiola, D. (2018). Energy use in recirculating aquaculture systems (RAS): a review. Aquacultural Engineering, 81, 57-70. Link to source: https://doi.org/10.1016/j.aquaeng.2018.03.003
Boyd, C. E., McNevin, A. A., & Davis, R. P. (2022). The contribution of fisheries and aquaculture to the global protein supply. Food Security, 14(3), 805-827, Link to source: https://doi.org/10.1007/s12571-021-01246-9
Food and Agriculture Organization of the United Nations. (2018). The state of world fisheries and aquaculture. Food and Agriculture Organization of the United Nations. Link to source: https://openknowledge.fao.org/handle/20.500.14283/i9540en
Food and Agriculture Organization of the United Nations. (2024). The State of World Fisheries and Aquaculture 2024 – Blue Transformation in action. Food and Agriculture Organization of the United Nations. Link to source: https://openknowledge.fao.org/handle/20.500.14283/cd0683en
Henriksson, P. J. G., Troell, M., Banks, L. K., Belton, B., Beveridge, M. C. M., Klinger, D. H., ... & Tran, N. (2021). Interventions for improving the productivity and environmental performance of global aquaculture for future food security. One Earth, 4(9), 1220–1232. Link to source: https://doi.org/10.1016/j.oneear.2021.08.009
Jones, A. R., Alleway, H. K., McAfee, D., Reis-Santos, P., Theuerkauf, S. J., & Jones, R. C. (2022). Climate-friendly seafood: the potential for emissions reduction and carbon capture in marine aquaculture. BioScience, 72(2), 123–143. Link to source: https://doi.org/10.1093/biosci/biab126
MacLeod, M. J., Hasan, M. R., Robb, D. H., & Mamun-Ur-Rashid, M. (2020). Quantifying greenhouse gas emissions from global aquaculture. Scientific Reports, 10(1), 11679. Link to source: https://doi.org/10.1038/s41598-020-68231-8
Naylor, R. L., Hardy, R. W., Bureau, D. P., Chiu, A., Elliott, M., Farrell, A. P., ... & Nichols, P. D. (2009). Feeding aquaculture in an era of finite resources. Proceedings of the National Academy of Sciences, 106(36), 15103–15110. Link to source: https://doi.org/10.1073/pnas.0905235106
Naylor, R. L., Hardy, R. W., Buschmann, A. H., Bush, S. R., Cao, L., Klinger, D. H., ... & Troell, M. (2021). A 20-year retrospective review of global aquaculture. Nature, 591(7851), 551–563. Link to source: https://doi.org/10.1038/s41586-021-03308-6
Scroggins, R. E., Fry, J. P., Brown, M. T., Neff, R. A., Asche, F., Anderson, J. L., & Love, D. C. (2022). Renewable energy in fisheries and aquaculture: Case studies from the United States. Journal of Cleaner Production, 376, 134153. Link to source: https://doi.org/10.1016/j.jclepro.2022.134153
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Stentiford, G. D., Bateman, I. J., Hinchliffe, S. J., Bass, D. 1., Hartnell, R., Santos, E. M., ... & Tyler, C. R. (2020). Sustainable aquaculture through the One Health lens. Nature Food, 1(8), 468–474. Link to source: https://doi.org/10.1038/s43016-020-0127-5
Tacon, A. G., & Metian, M. (2008). Global overview on the use of fish meal and fish oil in industrially compounded aquafeeds: Trends and future prospects. Aquaculture, 285(1-4), 146–158. Link to source: https://doi.org/10.1016/j.aquaculture.2008.08.015
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Seaweed (also called macroalgae) ecosystem restoration involves the reestablishment of wild red, brown, and green seaweed through interventions that recover degraded, damaged, or destroyed seaweed ecosystems. Healthy seaweed ecosystems remove CO₂ from the water column and convert it into biomass through photosynthesis, allowing additional CO₂ to be taken up in the ocean from the atmosphere. Some of this biomass carbon ends up sequestered, either on-site in sediment or off-site in the deep sea or at the seafloor. Advantages include the widespread human and environmental benefits associated with restored, healthy seaweed ecosystems. Disadvantages include its unclear effectiveness and climate impact, as well as its potentially high costs and difficulty of adoption at scale. Currently, we conclude that we should “Keep Watching” this solution.
Based on our analysis, the climate impact of restoring seaweed ecosystems is unclear but likely to be low. While restoration offers important ecological benefits, its effectiveness in removing carbon is understudied, and the implementation costs may be prohibitively high, but require further research. Therefore, we conclude that Restore Seaweed Ecosystems is a solution to “Keep Watching.”
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | No |
| Effective | Does it consistently work? | ? |
| Impact | Is it big enough to matter? | ? |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Seaweed ecosystem restoration is the deliberate action of reestablishing seaweed in degraded, damaged, or destroyed ecosystems. Seaweed removes CO₂ from seawater through photosynthesis, which allows the ocean to absorb additional CO₂ from the atmosphere. Some of the fixed carbon can be sequestered through export to the deep sea or burial at the seafloor, while a portion may also persist as carbon forms that resist degradation even in the surface ocean. Restoration of seaweed ecosystems helps restore biomass and therefore the productivity of these ecosystems, which can enhance their sequestration capacity. Restoration can occur in a number of ways, but commonly includes transplanting adults, controlling grazers, building artificial reefs, seeding with propagules or spores, remediating pollution, removing competitive species, and culturing. Most restoration efforts have focused on canopy-forming species, such as giant kelp (Macrocystis pyrifera).
Seaweed ecosystem restoration can be somewhat effective, with nearly 60% of restoration efforts achieving survival rates of over 50%. The first large-scale restoration is thought to have occurred in Japan in the late 1800s. Still, few projects have been implemented at scale, with most restoration efforts below 0.1 ha in size. Moreover, little data exist to evaluate the effectiveness of restored seaweed ecosystems at removing carbon. While theoretically, they should regain functional equivalence to intact systems, this requires further research. The extent of lost and degraded seaweed ecosystems is also poorly understood, making it unclear how restoration efforts might be scaled globally. Additionally, the air-to-sea transfer of CO₂ to replace the CO₂ taken up by photosynthesis in the ocean is not always efficient, meaning removal in the water column may not always translate to equivalent atmospheric CO₂ removal. However, this aspect of effectiveness also remains understudied. Consequently, the climate impact of restoration is uncertain.
Healthy seaweed ecosystems provide a range of ecological benefits. Seaweed can help buffer against ocean acidification in some places as functional systems better regulate pH. These systems also provide complex habitats that support a wide range of marine life, such as fish and invertebrates, so restoring seaweed ecosystems can help recover biodiversity. Seaweed ecosystem restoration can also improve nutrient cycling and overall ecosystem resilience to climate stressors.
Restoration of seaweed ecosystems is currently expensive, with costs varying widely depending on the method used. In kelp forests, chemical or manual urchin removal, which reduces grazing pressure, may cost between US$1,700/ha and US$76,000/ha in 2023 dollars, while most other approaches exceed US$590,000/ha.
It’s also unclear whether seaweed restoration efforts could scale enough to have a globally meaningful impact on GHG emissions. Using estimates from intact subtidal brown seaweed ecosystems, which are among the most productive and represent a likely upper limit on the effectiveness of seaweed restoration as a whole, restoration might remove 2.3 tCO₂‑eq
/ha/yr. At this rate, over 40 Mha would need to be restored to exceed 0.1 GtCO₂‑eq/yr.
However, most restoration projects are under 0.1 ha in size. For kelp forests, only roughly 2% (19,000 ha) have been restored out of the Kelp Forest Challenge’s target of 1,000,000 ha by 2040, suggesting that this practice may not be scalable currently.
The effectiveness of restoration can also be offset by the lifecycle emissions of products required to re-establish some seaweed ecosystems. For example, emissions from the production of cement blocks needed to afforest some seaweed habitats have been estimated to potentially delay carbon removal benefits for 5–13 years in some systems.
Bayraktarov, E., Saunders, M. I., Abdullah, S., Mills, M., Beher, J., Possingham, H. P., Mumby, P. J. & Lovelock, C. E. (2015). The cost and feasibility of marine coastal restoration. Ecological Applications 26, 1055–1074. Link to source: https://doi.org/10.1890/15-1077
Carlot, J. (2025). Restoring coastal resilience: The role of macroalgal forests in oxygen production and pH regulation. Journal of Phycology, 61(2), 255-257. Link to source: https://doi.org/10.1111/jpy.70019
Danovaro, R., Aronson, J., Bianchelli, S., Boström, C., Chen, W., Cimino, R., Corinaldesi, C., Cortina-Segarra, J., D’Ambrosio, P., Gambi, C., Garrabou, J., Giorgetti, A., Grehan, A., Hannachi, A., Mangialajo, L., Morato, T., Orfanidis, S., Papadopoulou, N., Ramirez-Llodra, E., Smith, C. J., Snelgrove, P., van de Koppel, J., van Tatenhove, J., & Fraschetti, S. (2025). Assessing the success of marine ecosystem restoration using meta-analysis. Nature Communications, 16(1), Article 3062. Link to source: https://doi.org/10.1038/s41467-025-57254-2
Eger, A. M., Vergés, A., Choi, C. G., Christie, H., Coleman, M. A., Fagerli, C. W., Fujita, D., Hasegawa, M., Kim, J. H., Mayer-Pinto, M., Reed, D. C., Steinberg, P. D., & Marzinelli, E. M.(2020). Financial and institutional support are important for large-scale kelp forest restoration. Frontiers in Marine Science, 7, 535277. Link to source: https://doi.org/10.3389/fmars.2020.535277
Eger, A. M., Marzinelli, E. M., Christie, H., Fagerli, C. W., Fujita, D., Gonzalez, A. P., Johnson, C., Ling, S. D., Mayer-Pinto, M., Norderhaug, K. M., Pérez-Matus, A., Reed, D. C., Sala, E., Steinberg, P. D., Wernberg, T., Wilson, S., & Vergés, A. (2022). Global kelp forest restoration: past lessons, present status, and future directions. Biological Reviews, 97(4), 1449-1475. Link to source: https://doi.org/10.1111/brv.12850
Eger, A. M., Baum, J. K., Campbell, T., Cevallos Gil, B., Earp, H. S., Falace, A., Freiwald, J., Hamilton, S., Lonhart, S. I., Rootsaert, K., Rush, M. Å., Schuster, J., Timmer, B., & Vergés, A. (2026). Creating a Global Kelp Forest Conservation Fundraising Target: A 14-Billion-Dollar Investment to Help the Kelp. Biological Conservation, 313. Link to source: https://doi.org/10.1016/j.biocon.2025.111573
Filbee-Dexter, K., Wernberg, T., Barreiro, R., Coleman, M. A., de Bettignies, T., Feehan, C. J., Franco, J. N., Hasler, B., Louro, I., Norderhaug, K. M., Staehr, P. A. U., Tuya, F. & Verbeek, J. (2022). Leveraging the blue economy to transform marine forest restoration. Journal of Phycology, 58(2), 198–207. Link to source: https://doi.org/10.1111/jpy.13239
Gibbons, E. G., & Quijon, P. A. (2023). Macroalgal features and their influence on associated biodiversity: implications for conservation and restoration. Frontiers in Marine Science, 10, 1304000. Link to source: https://doi.org/10.3389/fmars.2023.1304000
Kelp Forest Alliance. (2024). State of the world’s kelp report. Kelp Forest Alliance. Link to source: https://kelpforestalliance.com/state-of-the-worlds-kelp-report/
Martin, D. M. (2017). Ecological restoration should be redefined for the twenty‐first century. Restoration Ecology, 25(5), 668-673. Link to source: https://doi.org/10.1111/rec.12554
Pessarrodona, A., Franco‐Santos, R. M., Wright, L. S., Vanderklift, M. A., Howard, J., Pidgeon, E., Wernberg, T., & Filbee‐Dexter, K. (2023). Carbon sequestration and climate change mitigation using macroalgae: a state of knowledge review. Biological Reviews, 98(6), 1945-1971. Link to source: https://doi.org/10.1111/brv.12990
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