This Seaweed Was a Caribbean Disaster, Now It’s Gold

Author: Heather Hunsperger

Coauthor: Matt Ferrell

Video Editor: Sunny Natividad

Caribbean beaches are ankle-deep in slimy, smelly seaweed. Wave after wave of sargassum is blanketing shorelines from Barbados to Cancún. It traps sea turtles. It smothers coral reefs. And it drives tourists away from islands that depend on them. This seaweed isn’t just crashing weddings on the beach. It’s crashing Caribbean economies.

But what if sargassum wasn’t just a mess, but a raw material? What if we could turn it into bricks, biogas, and even buttery soft T-shirts? What if the right refining is all it takes to transform this weed into biodegradable packaging and high-performance composites?

This is the story of how Caribbean and international start-ups are transforming the seaweed invasion into a sustainable resource. And we all get the t-shirts.

Hundreds of millions of tons of seaweed have washed up on Caribbean and Mexican beaches since 2011. 2025 is already a banger year with 38 million tons arriving in May alone. And more is on the way for summer.¹

Caribbean communities are struggling to cope. Hotels have seen occupancy rates dip by 10%.² That’s because sargassum rots on the beach. It belches out fumes that smell like rotten eggs. It’s bad enough to drive off tourists and even close schools.³¹

Tourism isn’t the only thing that suffers. Thick mats of it clog the shallows. They sink and rot. They smother reefs and seagrasses. They kill fish.⁴¹⁵⁶

It’s a state of emergency for nature and for communities. The US Virgin Islands declared an actual state of emergency in 2022. The seaweed blocked the water intake for a desalination plant.⁷⁵

So what even is this mess?

The mess is sargassum. It’s a seaweed with tiny, air-filled buoys up and down its stalk that help it stay afloat.⁸ This type of sargassum never anchors to the seafloor. It spends its entire life drifting on the surface. It multiplies just by breaking into pieces. Those pieces grow into new plants. Kind of like how you can chop up a starfish and end up with five new ones. It’s the perfect setup for a runaway bloom.

For years this was okay. Sargassum stayed put in the Sargasso Sea. It’s a vast stretch of the Atlantic Ocean where looping currents permanently corral the seaweed. It’s like a lazy river with no exit.

The Sargasso Sea is the legendary sea that once stranded sailing ships in its windless calm. It’s where American and European eels migrate to spawn. And it’s in these floating seaweed mats that young loggerhead sea turtles grow up.⁹

Sargassum is a cradle of life. So how did it become a plague?

Scientists have puzzled over the origins of the seaweed invasion since the first mass stranding of sargassum back in 2011. Dead seaweed tells no tales. But satellite images do.¹⁰ The emerging consensus is that something happened in the winter of 2009. A year-long freak weather pattern sent strong winds over the Sargasso Sea. It pushed the weed east toward Europe. From there, it caught a ride in currents flowing south along West Africa. Then west across the Atlantic. This steered sargassum straight to the Caribbean.¹¹

That first invasion in 2011 wasn’t a one-off. Sargassum’s been like the Black Pearl of algae. It keeps coming back just when you think it’s gone for good. That’s because along its new southern Atlantic route, Sargassum gets even more sunlight to grow. And every spring and summer, wind and water conditions pull nutrients up from the deep. This fuels massive blooms.¹⁰

Now that we know this Sargasso Sea spin-off is here to stay, scientists have given it a name. The Great Atlantic Sargassum Belt. Possibly the worst rebrand ever. The belt must be massive. The tens of millions of tons of sargassum that swamp Caribbean beaches each year make up just 10% of the total biomass floating at sea.¹²

Most of the seaweed hits the windward coasts of the Antilles island arc and Mexico’s Yucatán peninsula. That’s Cancún, known for its long white beaches. They now face heavy landings from March to October.¹²³⁴

Hotels scramble to clean it up. But the costs are steep.⁴ Clearing just one kilometer of beachfront during sargassum season can run $70,000 a month. That’s three-fifths of a mile.¹³ Disposal is another headache. What doesn’t fit in landfill ends up in unofficial dumping sites.³

But what if we started treating sargassum not as waste to get rid of, but an opportunity to exploit? Not as a plague washing ashore, but a bumper crop?When life hands you seaweed, why not do like Señor Sargazo and make… houses? In Mexico’s Yucatan, Omar Vázquez has developed a way to turn sargassum into durable bricks. Each one is made with about 40% seaweed. A single home can lock away 20 tonnes of the weed. The very first one he built back in 2018 has already withstood five hurricanes.¹⁴ The bricks are durable. They’re cheaper to make than traditional bricks. And residents of sargassum brick houses say they stay cool in the summer heat.

Instead of houses, a team on the island of Grenada is making brownies. That’s because rotting sargassum releases methane. It’s the natural gas that fuels the ovens at True Blue Bay Resort’s House of Chocolate bakery.¹⁵ Benjamin Nestorovic founded SarGas in 2023. He feeds sargassum into a biodigester along with food waste and pig manure. Microbes break it all down and release methane. He captures it and sells it to the bakery.

SarGas now has government approval for a much larger digester and a biogas-fueled generator. It could turn 5,000-8,000 tons of sargassum each year into 150 kW of power.¹⁶¹⁷ That’s roughly the output of 1,500 home solar panels at typical capacity. This setup keeps running after sunset.¹⁸¹⁹ It’s only enough to meet a half-percent of peak demand. But for a small island that imports diesel, that’s a meaningful cut in both costs and emissions. It’s a step towards energy independence. Sargassum releases methane no matter where it breaks down. On a beach, in a landfill, or in a digester. You might as well put that gas to good use. If I’m choosing, I’ll take the solution that bakes my banana bread.

Like all the solutions we’ll talk about, this one can scale. It can process more seaweed and produce more energy over time.

That’s the idea behind Rum and Sargassum. It’s a start-up that grew out of Professor Legena Henry’s lab at the University of the West Indies on the island of Barbados.²⁰²¹ Her team fermented sargassum using wastewater from local rum distilleries and manure from the island’s blackbelly sheep. And with the methane they produced, they powered a car.

They say a $2,500, four-hour retrofit is all it takes to convert a gasoline engine to run on bio-methane. The goal now is to build a commercial operation to fuel the island’s cars and taxis with biogas made from seaweed and rum. As long as it’s the car that’s drinking and not the driver, I just might be on board.

But burning sargassum isn’t the only way to get rid of it. We can also slather it on our faces. Hear me out. Instead of fermenting sargassum for its energy, we can refine it to extract high-value materials. Like alginate, fucoidan, nanocellulose, and other multi-syllable words worth multi-millions.

Take alginate and fucoidan. They’re natural thickeners and moisturizers that the company Origin by Ocean extracts from sargassum. Founder Mari Granström ships seaweed from the Caribbean to her biorefinery in Finland.²² Those shipping costs are worth it. Alginate and fucoidan are used in products far more expensive per kilo than bio-gas. Cosmetics. There’s a certain irony in running screaming from this stuff on the beach, only to end up slathering it on your sunburned shoulders.

Origin by Ocean has also teamed up with Danish homeware brand Marimekko. They use Caribbean alginate to thicken the dye pastes behind their signature, colorful fabric prints. But wait, there’s more. Sargassum doesn’t just help print on fabric. It can also be fabric.

Entrepreneur Johanan Dujon from St. Lucia has spun out a company called Alt-Fibr. He extracts natural fibers from sargassum, banana stems, and pineapple leaves. That means turning beached seaweed and agricultural waste into paper products and food packaging that resists grease and water. These fibers could even be spun into lightweight, wearable cloth.²²³ Dujon is now working with Georgia Tech and the University of Maine to fine-tune his extraction process. When it’s ready, Alt-Fibr will be rescuing trees from paper mills. It will also be diverting sargassum from landfills.

And Alt-Fibr isn’t the only one seeing fabric potential in seaweed. Keel Labs is weaving soft cloth from a seaweed-based fiber now featured in Outerknown’s line of blanket shirts.²⁴ And a number of companies are fermenting seaweeds into bioplastics, similar to corn-based plastics, but without hogging farmland, freshwater or fertilizer. Loliware has created a seaweed-based, single-use straw,²⁵ and Sway is swaying fashion brands toward compostable garment bags made from kelp.²⁶ If you want to dive deeper into how seaweed could replace plastic, I’ve got a whole episode on that.²⁷

The tide of innovation is still coming in. Florida gets its own very unwanted share of sargassum washing ashore. Now, an Orlando company called Soarce wants to make it a happier place. If not the happiest place on earth. They’re turning all that weed into high-performance nanocellulose. Yep, one of those million dollar words.

Nanocellulose is a naturally occurring fiber found in plants and seaweeds. It’s incredibly lightweight. And it’s as strong as steel for its weight.²⁸²⁹ Like glass or carbon fiber, it can reinforce resins. You can mix it in to boost strength. Or use it as a nanoscale coating. Soarce sees potential for its seaweed-based version in everything from car doors and airplane panels to boat hulls and bike frames. Anywhere lightweight strength really matters.³⁰

Soarce extracts these fibers from sargassum using a custom solvent made from fruits and vegetables. Then they shear them down to just 100-500nm long and 50nm wide. That’s over a thousand times thinner than a human hair.³¹ The company tweaks the chemistry to create two Seabind™ additives. One is uncharged, for strengthening composites and coatings. One is negatively charged, for use in sticky stuff like adhesives and paints.

Founders Derek Saltzman and Mason Mincey recently put their seaweed-based additive to the test. They partnered with Oak Ridge National Laboratory and the University of Tennessee. They used industrial-scale equipment to reinforce carbon fibers with a thin coating of their seaweed-based nanocellulose.²⁸

Lighter, stronger materials made from a weed that’s choking Caribbean beaches. This is disaster opportunism. But in the very best way.

Sargassum is actually a better starter material than wood for a lot of applications. It doesn’t contain much lignin. That’s the woody part of wood that’s tough to break down. Even so, it’s got its own sugar-based polymers that can clog the works.³² It’s got a slimy little secret. Sargassum often absorbs arsenic and other heavy metals from its environment. These have to be stripped out for safe use.⁴⁵³³

This is already being done. But there’s still plenty of room to improve how sargassum is broken down. And to expand what we can make from it. To accelerate the science, Schmidt Sciences and the Foundation for Food & Agriculture Research have pledged up to $47 million over five years. This goes to researchers from eight academic institutions plus an industry partner.³²

At Princeton and Lawrence Berkeley National Lab, researchers are analyzing the compounds naturally produced when sargassum is fermented. And then reprogramming microbes to make even more valuable ones.

Scientists at the University of Puerto Rico are hunting for the microbes that make the most methane-rich biogas from sargassum.

And at UCLA, professors Aaron Moment and Ah-Hyung Alissa Park are cooking up hydrogen fuel from sargassum’s complex sugars. They’ve got quite the recipe. Just heat sargassum to 500°C or 932°F with sodium hydroxide. Also known as lye. Add nitrogen gas and a nickel catalyst. The result is 90% pure hydrogen gas. Plus a side of sodium carbonate.³³

The UCLA team is also working on ways to extract metals from sargassum. The goal isn’t just to clean out the arsenic. It’s to explore whether sargassum could be a source of critical metals for batteries and electronics. To recover metals bound in sargassum, scientists are testing molten salt electrolysis. It’s the same technique used to release aluminum from its ore. They’re also exploring whether the sodium carbonate byproduct from hydrogen production can be transformed into carbon nanotubes. Using that same electrolysis process.³³

That’s hydrogen fuel, potential battery minerals, and even carbon nanotubes. All from seaweed. And all of it from pesky biomass washing ashore. Not from drilling or mining.

It’s all thanks to a wave of creative entrepreneurs and scientists. They’re testing smart, potentially scalable ways to tackle the Caribbean’s seaweed crisis. But this isn’t the first time seaweed has been tapped as a sustainable material.

The blooms of sargassum washing up on Caribbean beaches each year might be a disaster. But they’re also raw material for innovation.