As awareness of regenerative agriculture grows and the importance of soil health for carbon sequestration spreads, we can spend a lot of time thinking of land as a climate solution. But we also need to talk about our oceans, which currently cover 71% of the Earth’s surface and absorb around 40% of carbon emissions.
As well as regeneration on the ground, ocean based farming (or regenerative aquaculture) can be an important tool in climate mitigation. And one of the key components? Seaweed.
Seaweed makes up half of all food farmed in the ocean. China, Indonesia, and the Philippines are the world’s top three producers, harvesting millions of tons each year and representing around 89% of global seaweed production. Here’s what you need to know about this wonderful plant, and how it could be key to a cleaner planet.
Seaweed’s carbon storage potential
Coastal ecosystems like mangroves and seagrasses are known for storing carbon. Often called ‘blue carbon’ ecosystems, they can take up to 20 times more CO2 per acre than forests on land. As they grow and die their leaves, roots, stems and branches, all of which contain carbon, become buried in underwater soil. Because of low oxygen concentrations underwater this material can be stored for decades before it eventually breaks down and releases CO2 again. However this carbon is stored close to shore, so can easily by disturbed by human activity, storms or runoff, releasing emissions sooner than necessary.
Seaweed was previously ignored as a carbon sink, as it tends to grow on rocky surfaces where it can’t be buried in soil or sediment. It’s also more likely to be eaten by animals or broken down by bacteria, both of which release stored carbon into water or the air.
However, this isn’t the full story. A study published in 2016 compiled data from previous studies to estimate how much carbon is removed by seaweed. The study found that wild seaweed is already responsible for sequestering over a hundred million metric tons of carbon each year, potentially more carbon than all other marine plants combined.
Seaweed is incredibly efficient when it comes to taking in carbon for growth. Highly productive species, such as kelp, can grow by as much as two feet per day. This seaweed then dies and decomposes into small pieces that drift to the ocean floor, taking carbon with them. Many seaweed species have gas-filled bladders that help them float on the ocean surface to access more sunlight for photosynthesis. This allows the seaweed to float long distances before eventually bursting and sinking to the ocean floor. Once in the deep ocean, the carbon in seaweed can be stored for centuries. CO2 behaves differently in marine sediments, remaining in liquid form and eventually turning into a stable solid hydrate as time passes. Because it’s stored far away from the shore, this carbon is less likely to be disturbed and returned to the atmosphere, potentially allowing it to be sequestered for millions of years.
Highly productive seaweed species can, therefore, contribute significantly to the carbon drawdown. It’s estimated that seaweed could sequester around 173 million metric tons of carbon annually, which is equivalent to the annual emissions of the state of New York.
Studies like this highlight the importance of protecting marine ecosystems like kelp forests, (which are also essential as biodiversity hotspots and providers of key ecosystem services). Carbon sinks are just as vital as decarbonisation, and plants like kelp can play a vital role in bringing down emissions.
Beyond this, it also demonstrates the immense potential of regenerative seaweed farming. Despite only taking up small areas of coastal regions, nearly 0.7 million tonnes of carbon are removed from the sea annually due to commercially harvested seaweeds. And there’s more that can be done.
The potential of seaweed farms
Seaweed farming already represents around 49% of global mariculture production, but its potential has not been fully explored. The way the ocean is currently farmed is also in dire need of improvement.
Far too much of the emphasis so far has been on fish. Farming fish requires lots of feed and can pollute waters with pesticides and antibiotics used to treat lice and disease, result in escapes that spread disease to nearby wild fish populations and generally require a lot of infrastructure and care. Improved feed options and technologies are trying to address these drawbacks, but to focus on honing fish production is to miss a greater opportunity.
The ocean’s ability to absorb carbon has led to ocean acidification, threatening shellfish and corals. Instead, ocean farming and marine permaculture can be used to absorb this carbon into plants, provide sustainable sources of food, and reduce ocean acidification. Scientists are exploring seaweed farming practises that mimic the natural process of seaweed drawdown into the deep ocean. Because of the speed of seaweed growth it can be incredibly efficient and easy to scale.
Preliminary models have estimated that no-harvest seaweed farms on just 3.8% of US West Coast waters could store 34.4 million metric tons of CO2 — an amount equal to all direct emissions from California’s agriculture industry
Shifting diets & regenerative farming
Incorporating more seaweed, which is essentially a vegetable, into diets can also take some pressure off soils. Seaweed is becoming an increasingly popular food source. While any carbon seaweed stores will return to the atmosphere when we eat it, the power of seaweed (or other regenerative aquaculture products) lies in using it to replace some of our land based food, which is more emissions-intensive to produce.
When seaweed farming is practised in tandem with certain types of animal aquaculture, it can deliver several climate benefits. Just as regenerative soil farming and permaculture on land creates integrated agro-ecosystems, seaweed can be grown in conjunction with shellfish. The seaweed absorbs excess nutrients and makes water less acidic, helping shellfish grow.
Farmers in China and Korea have used regenerative ocean farming practices for years, while the US is starting to see pioneers such as Greenwave, who grow seaweed and shellfish in small coastal gardens. Regenerative ocean farming mimics the diversity of ocean reefs by growing a mix of species, each playing a vital role. While seaweed draws in carbon, a single oyster can filter up to 50 gallons of water a day, taking nitrogen out of seawater and preventing the increase of ‘dead zones‘ where nothing can live in the water.
Both seaweed and shellfish require zero inputs, as they utilise sunlight alongside nutrients and plankton that are already in the water to grow, making regenerative ocean farming cheap and easily sustainable. It also removes the need for fish feed, chemical fertilisers or other synthetic chemicals, which are the primary sources of aquaculture pollution and carbon emissions. As well as improving water quality, the polyculture model create habitats for other species, increasing biodiversity.
Most vitally, they are able to provide large quantities of food while improving ocean conditions and absorbing greenhouse gases, rather than the degrading conditions of large commercial fishing farms or intensive land-based commercial agriculture.
While everyone may not be able to shift to a fully plantbased diet, this shows that even shifting from commercially farmed fish to regeneratively farmed shellfish, or replacing some non-regenerative vegetables with seaweed, can make a big difference. It has been estimated that shifting towards these more sustainable seafoods could reduce emissions by around 1 billion metric tons each year. Plus seaweed is a nutrient dense food that is rich in protein, iodine and other minerals, meaning the shift can be good for our health too.
And it doesn’t stop at humans. Integrating seaweed into livestock feeds has the potential to massively reduce the amount of methane produced by cows. Supplementing livestock feed with seaweed can reduce emissions from sheep and cattle by almost 60%.
Seaweed and biofuels
Plus, seaweed isn’t just used for food. It also holds a lot of potential when it comes to biofuel, especially as it grows faster and is more space efficient than other biofuel sources like soy and corn. One of the biggest criticisms of biofuel is inefficient use of land, so offshore seaweed farms can easily be scaled for biofuel production without wasting land.
The seaweed could be harvested and processed to generate methane for electricity production or to replace natural gas, and the remaining nutrients recycled. One analysis shows that if seaweed farms covered 9% of the ocean they could produce enough biomethane to replace all of today’s needs in fossil fuel energy, while removing 53 gigatonnes of CO2 (about the same as all current human emissions) per year from the atmosphere.
There is also increasing interest in using seaweed for a variety of other applications. There are many single-use plastic products that could be replaced with seaweed alternatives, seaweed can be used as a vegan alternative to gelatine, and it can also be an emulsifying agent in anything from food to beauty products.
In one of its more surprising applications, seaweed may also prove key to the construction industry, as it can be used for insulation and bricks. Seaweed can store 20% more energy than wood while also being mould-resistant and non-inflammable, meaning it can be used without any chemical additives and making it a commercially viable insulation product.
Could there be a time ahead where the building materials we use not only increase sustainability, whilst insulating and forming our homes, they also drawdown the CO2 we are actually producing inside the structure?
So, what can we do?
Protest & restore ecosystems
Just like rewilding on land, it’s vital we protect our marine ecosystems too. Mangroves, seagrass, salt marshes and other blue carbon ecosystems that have been degraded in the past, so restoration and preservation of these areas is key.
Learn more via The Blue Carbon Initiative
Change agricultural practices
Instead of continuing to rely on fossil-fuel–intensive manufacture of fertilizers, we can farm seaweeds that suck up carbon as they grow and can be used for food, animal feed, biofuels and fertilizer. Instead of pesticides making us and the ocean sick, we can grow food in the ocean that makes us well.
Rather than commercial fish farms or degenerative practices, more producers should be encouraged to shift to regenerative aquaculture. Greenwave offers a toolkit and training opportunities here for those looking to start a regenerative seaweed farm, or those looking to convert their models. Green Ocean Farming has a UK equivalent here.
Over 150 countries have at least one blue carbon ecosystem on their territory; in 71 countries all three types (mangroves, seagrass meadows and tidal marshes) exist. However, only 28 countries have included coastal wetlands in their nationally determined contributions (NDCs), the emission reduction plans submitted under the Paris agreement. There are two ways of looking at this omission: as highlighting the need for more countries to include blue carbon in their climate mitigation goals; or as an opportunity to drive investment in complimentary emission reduction activities on top of NDCs.
Many countries who already have blue carbon ecosystems don’t currently have protection and restoration outlines as part of their climate plans. Plus, many countries have extensive shallow waters suitable for seaweed cultivation that are currently not being used. If you are in a position to talk to your local political representative, pushing for targets for blue carbon protection, and incentivising more regenerative aquaculture in your local areas could be key to future food security and lowering emissions.
While there isn’t currently a huge directory of regenerative seaweed products you can easily scroll through, the following brands (both have food and beauty products) come recommended by regenerative wonder Holly Rose herself:
All in all, seaweed is a wonderful crop that may be key to a regenerative future. Here’s hoping it’s an area that continues to grow in the coming years.