Despite the frequent wash-ups of sargassum on the shores of Martinique and Guadeloupe, researchers and businesses have struggled to convert this nuisance into a reliable source of income. Yet these brown seaweeds could be used as fertilizers or as raw material for biomaterials.
When he sees his island’s beaches darkened by sargassum, Frédérick Voyer, head of the public interest group (GIP) Sargasses Martinique, can’t help but worry: he expects 2026 to be at least as bad as 2025, if not worse. That impression is in line with Météo‑France’s May 2026 assessment, which described the season as potentially “one of the most intense ever recorded” for strandings in the department. Guadeloupe faces a similar outlook: after removing almost 152,000 m3 of seaweed in 2025, the local GIP is braced for comparable volumes this year.
For around fifteen years now, hundreds of thousands of people across the French Caribbean have witnessed ever-larger sargassum arrivals on their coastlines. Researchers link the explosion of these blooms to shifts in ocean currents that have carried sargassum away from its natural habitat—the Sargasso Sea in the western Atlantic—bringing it close to the islands. There, warm, nutrient-rich waters seem to favor its growth. As the algae decay, they emit hydrogen sulfide and ammonia into the air. They can also concentrate heavy metals and residues of chlordécone, an insecticide. Those pollutants pose threats to public health, to ecosystems and to economies that depend in part on tourism.
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But the sargassum is not simply a calamity. France’s Agency for Ecological Transition (Ademe) points out that the algae represent a natural resource that could be turned into economic opportunities for the two departments. Some local initiatives already show potential. For example, Holdex Environnement, based in Le François in Martinique, has been able to produce good-quality compost from sargassum that is not contaminated with chlordécone, according to Charlotte Gully, an engineer specializing in the circular economy at Ademe. The company has been ready to operate for two years, but it still awaits official clearances that would confirm that its decontamination processes for heavy metals meet safety standards.
Voyer stresses why regulators move cautiously: the makeup of sargassum complicates processing and raises costs. It is essential to verify that the material is free of arsenic, chlordécone and other hazardous substances that would violate health and environmental rules. Such vigilance is needed to avoid future public‑health or ecological scandals.
There are promising laboratory and pilot results. In Guadeloupe, scientists have shown that biochar—produced by pyrolyzing sargassum—can partly remediate soils contaminated with chlordécone. The algae have also been trialed as a binder in concrete, as an ingredient for insulation materials and even as a feedstock for bioplastics. Yet the major hurdle remains moving those concepts from experimental stages to industrial-scale operations.
The number of project proposals is large. Ademe reports receiving heavy demand: since May of this year the agency has already been approached with nearly fifty ideas. Its task is now to separate the solid, scalable projects from more opportunistic or less reliable proposals.
Other structural obstacles make industrialization difficult, starting with the irregularity of beachings. Although strandings have been frequent and massive since around 2018, that has not always been the case. No significant arrivals were recorded in 2014 and 2015, and 2020 saw only limited strandings. That variability deters investors who fear financing processing plants that might sit idle in low years. Clio Maridakis, a marine biologist, points out a clear seasonality: sargassum typically appears between April and October, and outside that window only sporadic and minor arrivals occur.
Across the Caribbean, examples of durable, economically viable value chains built around sargassum remain rare. A study published by a consortium of researchers found that among the 28 countries most affected by sargassum, only 17 have managed to set up any kind of valorization pathway.
Mexico is often cited as a model. The country recently announced a large-scale program—about $158 million—to collect sargassum at sea, taking on responsibilities that had previously fallen largely to private actors. But for smaller territories like Martinique and Guadeloupe, establishing similar industrial systems is far more complicated. “We are small, sparsely populated islands with a limited industrial base,” Charlotte Gully observes. Designing facilities for island settings, and sizing them around a resource whose supply is unpredictable, is a genuine challenge.
Addressing that challenge is crucial. Satellite monitoring by the University of South Florida in 2025 estimated some 38 million tonnes of sargassum floating in the Atlantic and Caribbean—up from roughly 22 million tonnes in 2022—highlighting both the scale of the phenomenon and the urgency of finding sustainable ways to manage and potentially reuse this abundant marine biomass.
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Hi, I’m Ashley from the Decatur Metro team. I share essential information for a sustainable and responsible lifestyle.
