BY KATRINA MEGGET
Macroalgae – or seaweed – farming has taken off in recent years, spurring innovation. With 12,000 species spread around the world’s oceans, there’s a lot of untapped biomass ripe for harvesting. Katrina Megget reports
According to the UK’s Centre for Environment, Fisheries and Aquaculture Science (Cefas), there was just one commercial seaweed farm in the UK in 2016. Jump to 2022, and there were at least 10 active farms, while seaweed-related businesses have more than doubled since 2016, with at least 74 businesses across farming, processing, products and services in 2021. Similar trends are seen globally – in the US, for instance, seaweed farming is the fastest growing aquaculture sector, according to the US National Oceanic and Atmospheric Administration (NOAA).
The seaweed industry dates back hundreds of years but is entering a new era with the increased diversification of products and businesses, says Jenny Black, Project Manager of the Seaweed Academy, a training organisation that is part of the Scottish Association for Marine Science (SAMS). Seaweed components are already used in some toothpastes, cosmetics, paints and industrial products such as adhesives and dyes, but there is growing demand across pharmaceuticals, nutraceuticals, food ingredients, biotech applications and biodegradable materials.
‘Seaweed farming has taken off with increasing interest and investment in the blue economy [associated with the oceans and seas], health and wellbeing, with a focus on environmentally responsible sourcing of food and a need to diversify supplies of fertilisers and biostimulants,’ Black says. ‘The environmental benefits are definite drivers in the expansion of the industry and its products.’
As a result, many innovative businesses are emerging, from bioplastics to extracts for cosmetic products and seaweed-based materials for industrial applications. Black estimates the UK seaweed sector produces roughly 15,000 wet tonnes of seaweed through hand harvesting and cultivation. Globally, around 25-30m t/year is cultivated, says Steven Hermans, founder of seaweed industry economic information resource Phyconomy. China produces more than half of this, but interest is growing in Europe, the US and Australia. According to US analysts Research and Markets, the 2025 global seaweed cultivation market is worth almost $20bn and is expected to reach $33.26bn by 2030[1].
It all comes down to the unique properties and potential packed into these fast-growing, multicellular, photosynthetic marine organisms, of which there are more than 12,000 species (including ca 600 along the UK shoreline), which require just sunlight and seawater to thrive.
‘Seaweed grows up to 30 times faster than land plants, requires no fresh water, fertilisers or land, and sequesters massive amounts of CO2 while restoring marine biodiversity,’ explains Joyeeta Das, CEO and Co-Founder of UK-based Samudra Oceans, which uses robotics and AI to scale up seaweed cultivation. ‘Its structure absorbs nutrients [such as carbon, potassium, nitrogen and phosphorus], reduces ocean acidification and improves water quality. As a material, it’s a versatile feedstock for bioplastics, fertilisers, food and even biochar – making it one of the most regenerative and low input biomass sources on Earth.’
From an environmental perspective, Das describes seaweed as a ‘powerhouse’. It captures more carbon than trees, with some species absorbing up to 20 times more CO2/acre than land forests, she says. ‘It’s one of the only scalable solutions that captures carbon and restores ecosystems, while producing biomass that can be turned into climate-positive products.’
Seaweed’s environmental credentials and carbon capture capacity has generated huge interest.
However, the challenge is this would require massive scale-up, with limited scientific evidence on the impact of large seaweeds aquaculture in the deep ocean on both climate-change mitigation and marine biodiversity. But there is more to seaweed than just carbon capture. Increasingly, macroalgae is garnering attention because of its unique chemical composition, not found in other biomass.
Packed with vitamins and minerals, seaweed contains compounds like carrageenan (used as a food additive), the gelatine substitute agar, the polymer alginate (used in medicine) and seaweed’s own unique form of cellulose, which has wider cellulose chains than land plants, a more porous structure and little or no lignin. Along with that come seaweed-specific compounds such as fucoidan (a long-chain sulfated polysaccharide), laminarin (a beta-glucan polysaccharide), dieckol (a type of polyphenol), ulvan (a sulfated polysaccharide) and fucoxanthin (an oxygenated carotene). Many of these compounds have antioxidant and anti-inflammatory properties.
‘Algae can do things that other plants, fungi or bacteria cannot,’ Hermans says.
Environmental potential
A 2024 study by researchers at the University of California, Davis, US, found that feeding grazing beef cattle a seaweed supplement in pellet form reduced their methane emissions by almost 40% without affecting their health or weight – and even when eating the supplement voluntarily[2]. The results follow the team’s previous research showing that seaweed can cut methane emissions between 50% and 82% in other types of cows and cattle farming practices.
‘[These findings] are significant because livestock methane is a major contributor to agricultural greenhouse gases,’ says Ermias Kebreab, Professor of animal science at the University of California, Davis, who led the study. Livestock account for 14.5% of global greenhouse gas emissions, largely methane released when cattle burp. ‘Reducing [methane] at scale would substantially lower agriculture’s climate footprint while maintaining productivity,’ says Kebreab.
The research focused on bromoform (CHBr3) – a trihalomethane compound found in certain red seaweeds, which is produced as a defence mechanism. Kebreab says bromoform works to cut methane emissions by disrupting the final step of methane production in the cattle’s rumen. Specifically, it blocks the enzyme methyl-coenzyme M reductase that the methane-producing microbes use, preventing them from completing the methane-forming process. ‘Grass and other feeds don’t contain this compound, so they don’t have the same effect,’ Kebreab says. The team is now studying the long-term effects of feeding the supplement to cattle.
Beyond more sustainable agriculture, seaweed could also help to reduce plastics’ pollution. A team at Aberystwyth University, Wales, has developed a biodegradable seaweed plastic using sodium alginate from brown seaweed. The compound produces a highly transparent, soluble plastic film, explains Jessica Adams, a senior research scientist in bioconversion and biorefining. ‘Sodium alginate is relatively simple to extract or can be bought pre-extracted at food grade. You literally add water and stir until dissolved, then pour into a mould. Once set, you have your film.’
Degradation is almost instantaneous; the film can be dissolved within a minute of being added to water or takes a few weeks when composted. And by adding plasticisers such as glycerol or cellulose, the film’s shelf life can be extended. These compounds can also make the film stronger or more flexible, Adams adds. The research has recently been submitted for peer review.
Meanwhile, adding calcium – in the form of calcium carbonate or calcium lactate – makes the film insoluble, because calcium ions bind to alginate acids. This could be beneficial for food packaging but also in a medical setting where surgical implants or wound care made from thicker forms of alginate slowly solubilise in the body after the calcium is naturally removed and replaced by sodium. As a result, no secondary removal procedures would be needed, Adams says. Her team has also explored adding antimicrobial compounds to films.
‘This is an area of great potential,’ Adams says. ‘Replacing plastic liners in single-use items like coffee cups and takeaway boxes is where the initial shift would be seen but there are many opportunities to replace other items as well.’
Another area seaweed could make an impact is in biofuels production. Several research institutes have sought to use seaweed to produce biofuel. Currently, millions of tonnes of rotting seaweed wash up on the beaches of Mexico and the Caribbean, impacting the tourism and local fisheries industries. The University of the West Indies, for instance, has harnessed this waste to power a vehicle by bio-compressed natural gas sourced from seaweed.
Unlike first and second-generation biofuel feedstocks, seaweed is a third-generation feedstock that isn’t diverted from food use and doesn’t require land or freshwater to grow.
According to a 2021 journal paper, led by the Central University of Tamil Nadu, India, ‘macroalgae is perhaps the most potential non-consumable biofuel source… and has advantages such as rapid growth… and ease of cultivation, which has the potential to meet the energy crisis’[3].
However, the biorefinery process is not without challenges. These include the complex structure of algal biomass and the need to remove salt. Being able to scale up production while maintaining environmental sustainability is another big challenge currently limiting expansion of seaweed biofuels.
According to a 2012 report by the University of the South Pacific, if 9% of the world’s ocean surface was covered in seaweed farms, that could produce 12bn t/year of biomethane which could substitute for natural gas. ‘[This] could produce sufficient biomethane to replace all of today’s needs in fossil fuel energy, while removing 53bn t of CO2/year from the atmosphere, restoring pre-industrial levels,’ the authors write[4].
Meanwhile, an EU-funded MacroFuels project exploring the potential of seaweed as a biofuel, suggested in 2019 that if 2.5% of transport energy in the EU came from advanced biofuels (an EU 2020 target), an area of 5000km2 would be needed for seaweed cultivation[5]. While the intent might be there, the logistical and economic challenge remains.
‘Biofuels can be made from seaweeds but for them to make a meaningful difference in the global supply of energy, seaweed production would have to increase by at least a factor of 100 to approach the volumes needed and for it to be able to compete with the price of petroleum,’ Hermans says. ‘Not any time soon, in other words.’
Business potential
Many people have questioned the economic viability of seaweed businesses in general. Yet, research continues to explore innovative uses of seaweed and its components. For instance, scientists have explored seaweed-derived materials to store heat, and to create next-generation batteries as well as for their anti-inflammatory, anti-cancer and antimicrobial properties for use in medicine or as cleaning products and food preservatives.
Growing demand is shifting the balance, with many countries pushing further development. In June 2025, the UK’s Cefas published new regulatory guidance for applying for marine licences for seaweed aquaculture, with the aim of making the process easier to navigate, previously regarded as a bottleneck.
Meanwhile, the i3-4-seaweed project in the EU, aimed at scaling business in the seaweed sector, announced in August 2025 that €1.8m would be available for up to 30 projects in macroalgal production and algal biotechnology and downstream applications – and called for SMEs in eligible EU regions to apply.
According to the authors of the Research and Markets report: ‘[The] confluence of technological prowess and regulatory alignment sets the stage for an era where seaweed cultivation is recognised as a cornerstone of the blue economy, driving both environmental resilience and economic vitality.’
Hermans agrees that seaweed ticks a lot of boxes. ‘In the future, seaweeds will be part of the ink, the cardboard and coating on your meal container,’ he says. ‘The fries in the meal container will come from potatoes sprayed with seaweed biostimulants. Materials will be treated with seaweed nanocellulose to make them more performant, while your socks might contain a bit of seaweed fibre.’
As the world transitions to a bioeconomy, it is clear the blue economy will play a role. How much of a role has yet to be determined but undoubtedly seaweed will contribute to powering that green – or red, brown or blue – future.
References
- Research & Markets, 2025
- P. Meo-Filho et al, PNAS, 2024, 121 (50), e2410863121.
- G. Sharmila et al, Bioengineered, 2021, 12, 2, 9216.
- A. de Ramon N’Yeurt et al, Process Safety and Environmental Protection, 2012, 90, 467.
- European Commission: CORDIS - EU research results
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