Every year, vast quantities of sargassum seaweed wash up on the shores of the Caribbean Sea and Gulf of Mexico, threatening coastal communities’ economies and ecosystems. Comprising two free-floating species (Sargassum natans and Sargassum fluitans), the macroalgae is by no means new to the region. Until a decade and a half ago, its seasonal proliferations were limited for the most part to the calm waters of the Sargasso Sea, which lies between Bermuda and the Azores at the center of the great North Atlantic Subtropical Gyre. Back then, manageable quantities of the seaweed would drift each year into Caribbean and Gulf waters.

Since 2011, however, annual sargassum blooms have covered a far larger area of the central Atlantic Ocean, their volumes estimated in some years to total over 20 million tons. What scientists call the Great Atlantic Sargassum Belt sometimes stretches from the Gulf of Mexico to West Africa, pushing far larger quantities of the unanchored seaweed into the Caribbean and Gulf of Mexico than typically was the case before 2011.

Some researchers have attributed the phenomenon to a 2009-10 climate event that they say has altered atmospheric pressure over the North Atlantic. They argue this shifted currents and winds in such a way that sargassum now extends farther east and south into warmer tropical Atlantic waters, where it grows at a greater rate and catches currents that distribute it more widely. Scientists have cited other contributing factors—among them larger quantities of nutrients entering the Atlantic from the Amazon and Congo River watersheds due to runoff from the industrial-farming operations proliferating in the two regions.

Sargassum, to be sure, provides important ecological benefits. At sea, the floating mats it forms serve simultaneously as shelter and food source for a wide variety of marine species. And on land it helps firm up beaches, becoming compost for seaside plants. But experts fear sargassum poses serious environmental and economic threats as growing quantities of it foul resort beaches, smother coastal marine habitat, and—as it decomposes in intertidal zones—sends greenhouse gasses into the atmosphere. In response, scientists and entrepreneurs are looking for ways not only to manage sargassum’s negative effects, but also to turn the seaweed into an asset, incentivizing its collection and creating new income sources.

Defensive strategies range from the deployment of floating booms aimed at blocking sargassum from reaching key coastal areas to possible deep-water sinking of the seaweed with the goal of confining it to the ocean floor—along with its carbon—for centuries. In Barbados, experts have concluded that even if their country moves to commodify sargassum, the enormous quantities of seaweed washing up on the island’s eastern shores still justify the adoption of a disaster risk-management plan. Authorities there aim to draft such a blueprint in line with the 2015 Sendai Framework, a 15-year United Nations agreement to help member countries anticipate and minimize disaster risks.

Simultaneously, countries are exploring entrepreneurial approaches, eyeing large-scale collection and use of sargassum as an ingredient in products such as biofuel and natural fertilizer, and potentially others ranging from pressed wood and vegan leather to pharmaceuticals and skincare products. The possibilities have spurred a variety of activities in the field, leading some to see a positive flip side to the sargassum crisis and even to describe the seaweed as “Caribbean Gold.”

Mexico’s southeastern state of Quintana Roo is hoping to help address the sargassum problem through seaweed-based biogas production—and reduce greenhouse-gas emissions in the process. Home of the Riviera Maya coastal-resort region and its 140,000 hotel beds, the state can ill afford sargassum-covered beaches. But according to a report by the Inter-American Development Bank, 4% of sargassum entering the Caribbean reaches the state, depressing tourism to the tune of 11.6% from 2016 to 2019.

Miguel Montesino, northern Latin America director of the Spanish standards firm Aenor, is working with Quintana Roo officials on the sargassum-to-biofuel effort. He says the initiative aims to certify the resulting greenhouse-gas emission reductions to generate credits for sale in voluntary carbon markets. Scaling the public-private project poses challenges, however, not least because it must assume a predictable annual sargassum supply. “Sargassum as a raw material is not reliable,” says Montesino. “We might have a large influx in a certain period of time, and a sudden digression if the currents change. So we are trying to move forward based on an average figure of sargassum.”

Sargassum is not the most efficient feedstock for biogas production. It needs to be mixed with waste from such sources as sewage-treatment systems or distilleries to produce a fuel source with clear climate benefits. Montesino says one ton of sargassum can release 1.3 tons of CO2 if left to rot, while producing and burning sargassum-based biogas causes significantly smaller net carbon releases.

The project goal is to sell methane to a gas-fuel company, transporting it in tanks or through a pipeline. The resulting green gas could replace fossil fuel-based gas that hotels, for instance, use to run laundry boilers. Current plans call for a six-biodigester plant capable of processing 500,000 tons of seaweed a year, with each biodigester working at 75% of capacity. Organizers hope to finance the estimated US$300 million project with help from investors including the World Bank and Inter-American Development Bank.

Among the most fundamental questions facing project organizers is how best to collect the sargassum. Says Montesino: “Sargassum is not gold or diamonds, so a price cannot be easily set for a ton of seaweed. The crews needed for cleaning the coasts of Quintana Roo would be 250 for the state’s 800 kilometers [500 miles] of coastline and would generate 2,500 formal jobs. The Pareto ‘principle of factor sparsity’ must be changed: Collect 80% at sea with crews and let the remaining 20% ​​reach the beach to avoid the problems of coastal erosion caused by collecting on land, as coastal towns like Puerto Juárez have already run out of sand.”

Robotics entrepreneurs are targeting sargassum, too. Seaweed Generation, a UK-based start-up, aims to operate within the waters of Caribbean countries’ Exclusive Economic Zone (EEZ). The company has built and tested a robot it calls AlgaRay, which collects seaweed on the ocean’s surface. After filling its open cavity with sargassum, the solar-powered, manta-ray-like glider descends deep enough to ensure that increased water pressure compresses the macroalgae’s air sacs to the point the sargassum loses its buoyancy. Then it dumps the seaweed, which settles on the ocean floor. Though AlgaRay, the company’s first robot, is designed to sink seaweed in the deep ocean, the technology also could be used to collect sargassum in near-shore waters for onshore processing or disposal.

“We are removing carbon, not offsetting it,” says Patricia Estridge, software engineer, CEO and Co-Founder of Seaweed Generation.

“We could process sargassum, turn it into liquid and sequester it on land using Vaulted’s slurry injection technology for carbon removal,” Estridge says, referring to a system developed by Vaulted, a carbon-removal company, to provide deep-well injection of biosolid waste. “We would use a mothership [working with] a group of small vessels running on solar panels.”

All such plans assume income from carbon credits based on avoided greenhouse-gas emissions, since sinking seaweed in the deep ocean, or turning it into slurry and injecting it deep underground, would theoretically prevent release of greenhouse gasses. “Carbon credits with sargassum aren’t going to reach gigatons,” Estridge says, “but they can help us understand carbon dioxide removal with seaweed more broadly, and potentially reduce a horrible problem at the same time.”

Currently in a data-collection stage as it prepares project proposals, Seaweed Generation must determine—among other things—how much sargassum it could sink without impacting deep sea ecosystems. It also aims to study which areas of the seafloor could safely accommodate such deposits, and what happens to the seaweed biomass over time on the ocean bottom.

“Luckily, we have time to do this work, as carbon markets are currently in a state of flux,” Estridge says. “Carbon credits, or the money made from them, within each EEZ would be shared with the governments, but the removal beneficiary [governments, communities, or investors, for instance] has yet to be determined and eventually it will depend on the legal structure of each country. We hope to be operational within the next three to four years, but it will take us at least five years for monitoring studies. By 2030 we should be ready to go.”

In the Dominican Republic, addressing sargassum’s impacts are a major concern. “Dominican diplomacy has made sargassum a fundamental issue in all environmental forums,” says Jimmy García, president of the National Authority for Maritime Affairs (Anamar), the government’s main marine-research arm. “There is a public-private [body] dedicated exclusively to sargassum research…universities are looking for solutions to find a product that can use sargassum as an input.”

Such research is beginning to produce actual products. A Caribbean-wide initiative called Harvesting Hope from the Sea, for instance, has produced two: Marine Symbiotic, a natural biostimulant for crops, and Marine Blossom, a sargassum-based substance that can extend the lifespan of fresh-cut flowers. Both reflect the same complementary aims: to spur sargassum removal by giving local fishers a means of making extra money. So far over 120 fishers in the region are taking part.

García worries about cost issues, given the expense of sargassum collection and processing. “A country like the Dominican Republic cannot dedicate resources to subsidizing products resulting from sargassum,” he says. “Therein lies the dilemma.” For now, most Dominican sargassum efforts focus on forecasting and communications, including the use of satellite-monitoring information to alert hotels, power plants and municipalities when sargassum flows are expected. Forecast failures—for instance, when overcast skies prevent continuous satellite monitoring—can prove costly. Officials say a power plant idled to clear clogged turbines can represent a loss of $700,000 a day.

Fertilizer and more

Ulises Jáuregui Haza, coordinator of an interdisciplinary sargassum research group at the Santo Domingo Institute of Technology (Intec), says his team’s main focus has been sargassum-based fertilizer. Other uses for the seaweed are being explored as well—for instance in making charcoal and pressed-sheet wood substitutes. Jáurgegui notes only 5% of a given quantity of sargassum can be used in highly refined products such as drugs and beauty products, with the seaweed’s remaining fibrous biomass suitable for other purposes ranging from bioenergy to construction materials. But work on value-added products is nevertheless progressing. The Finnish algae-refining company Origin by Ocean, for instance, is using seaweed to replace synthetic products such as dyes in the clothing industry.

Jáuregui acknowledges that efforts to exploit sargassum are dogged by “insufficient financial support for research and uncertainty on the part of some entrepreneurs, given that the quantities, dates and places of arrival of these algae are difficult to estimate.” He adds: “Another challenge is that regional integration has not yet been achieved to deal with the situation generated by sargassum.”

Such hurdles are being discussed in fora including the 2nd EU-Caribbean Global Gateway Conference on Sargassum, which took place Oct. 1-2 in Grenada. Held by the European Union and the Organization of Eastern Caribbean States (OECS), the meeting followed an inaugural conference last year in the Dominican Republic.

Mari Granström, CEO and founder of Origin by Ocean, says that while last year’s conference focused on defining the sargassum problem, this year’s identified courses of action—and the need for financing to pursue them. Says Granström: “There is a lot of money out there, and now we must mobilize it toward the [sargassum products’] supply chain.”

Introducing the “Sargometer”

Other important information sources on sargassum strategy are forming, too. The Inter-American Development Bank, for instance, issued a report in August on innovation and governance in the field. It has also developed a “Sargometer,” an evaluation tool to inform entrepreneurs on important factors affecting the sustainability and effectiveness of particular solutions. And the bank provides case studies highlighting the sargassum-related products emerging, as well as community perspectives on different technological solutions.

Few experts expect such efforts to stem the sargassum tide anytime soon. Rosa Rodríguez, a marine biologist and researcher at the Institute of Marine Sciences and Limnology of the National Autonomous University of Mexico (UNAM), views the inundations as unstoppable. She argues for importing containment barriers, which to date in Quintana Roo, she says, only cover 18-kilometers (11 miles) of the state’s 800-kilometer (500-mile) coastline.

Rodríguez adds sargassum must also be subject to special waste handling, given the oil, pesticides and other pollutants it encounters at sea. Meanwhile, she says, the seaweed’s impacts continue: “The brown tide reaches its greatest extent in the calmest bays and causes the water to darken, increasing its temperature and decreasing the oxygen concentration and pH. This affects flora and fauna, including corals.”

(This article was produced in partnership with the Pulitzer Center.)