Finnish diver and organic chemist Mari Granström has spent decades exploring the oceans. More than 20 years ago, while mapping marine biodiversity, she began to notice a worrying pattern: certain species were disappearing. At the same time, sargassum and other invasive seaweeds were spreading, not only across the Atlantic Ocean and along Latin American coastlines, where the blooms were most visible, but also in parts of Southwestern Europe, including Spain and Portugal.
Sargassum is a genus of large brown seaweed (a type of algae) that floats in island-like masses and never attaches to the seafloor, according to the US National Oceanic and Atmospheric Administration. It is considered an invasive species due to its rapid growth and propagation. Before 2011, sargassum was mostly confined to the Sargasso Sea in the North Atlantic. But now, it is spreading across the Caribbean Sea and the Gulf of Mexico, clogging otherwise pristine beaches and undermining the ability of local communities to make a living from tourism and fishing.
In May, a record 37.5 million metric tonnes of sargassum was seen in the Atlantic Ocean, the UN Environment Programme reported. This summer, it was declared a regional emergency. At the UN Ocean Conference in France in June, during a side event about the sargassum crisis, the Dominican Republic’s Minister of Environment and Natural Resources told attendees that this reflects the growing impact of sargassum as a “transboundary phenomenon”, affecting the “economic development, public health, marine ecosystems and energy security” of the Caribbean.
For coastal communities across Latin America — many of which are already on the frontlines of the climate crisis — it’s a double blow. The rising ocean temperatures and nutrient pollution (from agriculture and deforestation), which are accelerating the spread of sargassum, have already decimated coral reefs and hindered fishing and tourism. Now, there’s another issue to contend with: when massive blooms of sargassum rot — which often happens as they mount on beaches — they can release toxic gases that irritate the skin and cause respiratory problems, warns Juan Carlos García, a PhD candidate in sustainable development. Not to mention the smell.
In response, startups across Latin America, the US and Europe are racing to transform this invasive seaweed into textiles, dyes and cosmetics, with established brands starting to take note.
Harvested properly, experts say sargassum can be a versatile resource. The multifaceted seaweed contains a biopolymer called alginate, which can be used as a natural thickener. In the textile industry, it can help prevent ink from bleeding, intensify colour and improve print quality when used as a pre-treatment. When moulded and dried into flexible films, it can even imitate vegan leather, and combined with additives and natural dyes, it can serve as an alternative to polyurethane coatings for bags and accessories.
Sargassum alginate can also be processed into fibres through a process called wet spinning, where it’s turned into a viscous gel and ultimately forms filament-like structures. These fibres are fragile when dry, so they’re often combined with other biopolymers to improve durability and are being explored for use in textiles and composite materials as a more sustainable alternative to synthetic fibres like polyester.
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In the cosmetics world, sargassum alginate could replace other petroleum-based ingredients, helping brands reduce their carbon footprints. Sargassum itself also holds a hidden skincare gem: fucoidan, which can have anti-inflammatory and hydrating properties.
Early promise, but scale remains elusive
While most companies turning sargassum into textiles, dyes or biochemicals are based far from the affected coastlines, SOS Carbon is one of the few operating directly at the source: the Caribbean. SOS Carbon is a spin-off organisation from the mechanical engineering department at the Massachusetts Institute of Technology (MIT), founded in 2018 by Dominican climate tech entrepreneur Andrés Bisonó, together with Dr Alexander Slocum. They began by developing a way to collect sargassum — dubbed the Littoral Collection Module (LCM) — and officially registered as a company in 2020.
SOS Carbon is now based in Punta Cana, east Dominican Republic, and has collected over 15,000 tonnes of sargassum to date, which is mounted onto boats that intercept the floating blooms. It mostly harvests along Dominican coastlines, but has also expanded to Mexico, Antigua and Barbuda, and Puerto Rico. The sargassum is then dried and stored, all before it can reach the beaches of Punta Cana, where the Atlantic meets the Caribbean Sea and luxury resorts host millions of tourists each year.
One of SOS Carbon’s main allies is Origin by Ocean, the Finnish biochemical company Granström founded in 2019. Origin by Ocean has developed and patented three compounds from sargassum: Oceanthix and Caerulo (alginates), and Oceanboost (fucoidan). However, it has yet to reach commercial scale: production will ramp up from the second quarter of 2026, with full production capacity following by 2027.
“While highly purified fucoidan is expensive to produce, its concentrated nature makes it effective even in low dosages,” explains Granström. “While we don’t expect it to be a viable option for brands that compete only on price [rather than on the quality and performance], we are developing our range of Oceanboost fucoidan to be inclusive to nearly any brand committed to offering consumers high-performance, science-backed and clinically proven skincare.”
For now, Origin by Ocean is focused on collaborating with fashion brands, including Finnish design house Marimekko, which has piloted sargassum from the Dominican Republic to replace synthetic chemicals in its print paste. This resulted in a capsule collection printed with Caerulo alginate, sold in Finland and Europe, according to Marimekko communications director Anna Tuominen.
On the other side of the Atlantic, Keel Labs, founded in 2022 and based in North Carolina, has developed a bio-based fibre known as Kelsun, which is also free from plastic and tree-derived products. This material is extracted from various types of brown seaweed, including, in some cases, sargassum. “We work with a specific biopolymer that comes from a number of different seaweeds — the polymer isn’t limited to one species,” says Keel Labs co-founder and CEO Aleks Gosiewski. Keel Labs has worked with sargassum from different sources, including the Caribbean, she adds. “Sargassum is more of a warm-water seaweed, so most of the places we source it from have warmer seasons for longer.”
The company is starting to break through with mainstream collaborations, Gosiewski continues. Kelsun has been used by LA surf brand Outerknown, in Other Stories’s summer 2025 beachwear collection, and by Stella McCartney, whose $200 million SOS Fund has also supported Keel Labs. According to Gosiewski, textiles made out of these algae have been described by customers as the softest thing they’ve ever touched, dubbing it “the cashmere of the ocean”.
Still, commercial scale remains elusive. “When it comes to making the actual fibre, we are not producing it commercially today, although our material is on the market,” Gosiewski says. “It’s a little bit more expensive than fibres that you can readily purchase and are used today. We have a line in sight to get to a cost that is much more competitive with other materials on the market. But today, just given our stage and scale, the costs are a little bit higher.”
Mobilising finance
In 2023, Origin by Ocean received €7.5 million in seed funding: €3 million in private funds led by Voima Ventures and Lifeline Ventures, and a €4.5 million loan from Business Finland, which was used to pilot industrial-scale algae refining and commercialise the process. According to Granström, the company is looking to boost this through a series A round funding its first commercial production plant.
The planned facility will be in Finland, enabling Origin by Ocean to scale up significantly. The goal is to reach full capacity by 2028, processing 4,000 tonnes of sargassum per year, and in turn, producing 63 tonnes of alginate and 24 tonnes of fucoidan. A second facility will hopefully follow in the Caribbean by 2032, at which point the Finnish site will transition to exclusively processing sargassum from local European species. “This strategic approach helps us efficiently build our first commercial production plant and prepare for a larger investment in the Caribbean, where existing infrastructure is less developed,” says Granström.
In the case of SOS Carbon, the revenue generated has been reinvested into scaling operations. The company is able to sell sargassum to the final consumer for approximately $16 per litre, but that alone cannot sustain the company’s growth. Research and development, certifications and equipment adaptation require years of testing and funding, says Elena Martínez, SOS Biotech co-founder. To move forward, SOS Carbon has received prizes and support such as from MIT Solve, the UN, the International Trade Centre and the G20 Global Land Initiative — but more is needed.
Once these operations are up and running, sargassum startups will have to secure brand partners to use their products. While Keel Labs has been supported by McCartney’s SOS Fund, it is not immune to the challenges other next-gen material innovators face securing offtake agreements and commitments from brands to actually use the material once it has been produced. “We need to make sure that we have enough commitments to move on to the next stage,” says Gosiewski. “It’s important for us to have as many brands as possible working with the material, building confidence around the material and then also committing to purchasing larger volumes of the material.”
“Seaweed-based alternatives are still significantly more expensive than fossil-based or synthetic materials in key categories,” says Jorge Vega Matos, part of the founding team of Carbonwave, a company that develops biomaterials from seaweed, mainly sargassum. Companies like Carbonwave and SOS Carbon have had some early success by tapping into the bloom at the source, but “doubts remain about the consistency of supply on a year-on-year basis”, Matos adds.
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Marine scientist Jessica Giannotti explains that while sargassum blooms are likely to keep happening due to climate change and excess nutrients from rivers like the Amazon, the quantity and location can be unpredictable, and is likely to shift over time. In some places, the seaweed that’s abundant today could disappear tomorrow, and show up in areas where there is no infrastructure to deal with it.
Building a viable sargassum supply chain also means reckoning with the unknown qualities that come with invasive species, says Thamires Pontes, founder and CEO of Brazilian biotech startup Phycolabs, which turns seaweed harvested directly from the ocean into textile fibres. “Because it’s an invasive species, we don’t always know what’s inside sargassum, or what metals, nutrients and microorganisms might be present,” she explains. “To transform it into something useful, it must first be thoroughly cleaned, which is a whole process in itself.”
The bigger picture
If the push for sargassum-based products is to support the communities affected by its invasion, then the only truly just and lasting solution is to tackle the root cause, says Steve Maximay, a science advisor for the Association of Caribbean Media Workers (ACM). He argues that using sargassum in fashion is a reactive approach — it assumes we will continue living with such blooms long enough to sustain an entire industry. “We need to reduce the blooms at their source, by lowering ocean temperatures and minimising nutrient spikes. There have even been suggestions of sinking the sargassum, seeding it to kill it and sending it to the ocean floor,” he says.
Affected communities have their sights set on legislation. Last June, the Dominican Republic, together with Mexico, Costa Rica and France, submitted a draft resolution for consideration at the upcoming United Nations Environment Assembly, to strengthen early warning systems and satellite monitoring and mobilising international financing for affected countries and communities, among other suggestions.
To navigate this uncertainty, the emerging industry will have to work together, says Giannotti. “Collaborating and managing risks is vital for an emerging industry, along with the jobs and economic and social benefits it brings in rural and coastal areas, where economic stability is already vulnerable and impacted by a rapidly changing climate,” she says.
With the right level of investment — and buy-in from policymakers — sargassum could capitalise on a fledgling “blue economy”, Giannotti adds. “If we inject capital and investment in the blue economy, we can create long-term value for all and align communities and businesses, while securing strong political will.”
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