Francisco Neto is a Brazilian fisherman, Rosa Rodríguez is a Mexican scientist, and Renelle Kissoon is a local representative from Trinidad and Tobago. They have never met. Their countries have specific cultures. They even speak different languages. They are tangled however by a common problem: a huge carpet of sargassum - a kind of algae - that periodically covers large areas of the Central Atlantic, spanning many countries from the Gulf of Mexico to Africa.

Sargassum is so thick that made Francisco’s boat capsize dramatically in 2024. It is so abundant that Renelle Kissoon doesn’t know where to safely dispose of it. It is so disruptive that steered Rosa’s career towards understanding it and finding solutions to the problem.

Sargassum is a genus of floating brown macroalgae named after the Sargasso Sea in the North Atlantic, where it naturally forms massive mats.

However, the sargassum that impacts Brazil, Mexico and Trinidad & Tobago, among other countries, originates from the Great Atlantic Sargassum Belt, which covers a vast region in the Central Atlantic. A 2019 study published in Science reported that this phenomenon has grown exponentially since 2011 due to a combination of environmental and anthropogenic factors.

Climate change has increased ocean temperatures, creating ideal conditions for its proliferation. Warmer waters accelerate sargassum's metabolism, allowing it to grow faster and in more significant quantities. Meanwhile, the influx of nutrients like nitrogen and phosphorus from land-based sources has created a "marine fertiliser" for the algae. These nutrients primarily originate from agricultural activities in South America, where intensive fertilizer use in the Amazon basin ultimately reaches the ocean. This nutrient overload combines with organic material from deforestation and heavy rains, creating the perfect breeding ground for sargassum.

Changes in ocean circulation patterns, attributed to climate change, have further redistributed the currents that carry sargassum from its origins to the Caribbean coasts, explaining why the issue has intensified over the past decade.

When Sargassum is floating in the ocean, it provides nursery areas for fisheries, a habitat for juvenile fish, and several ecosystem services, like sequestering carbon dioxide out of the atmosphere and ocean. However, as it drifts toward nearshore areas and ultimately lands on coastlines, these massive mats of seaweed can prove disastrous for those who are unfamiliar with the hazards they bring.

Almost a year ago, artisanal fisherman Francisco Neto, in the Brazilian Amazon, nearly lost his life when a sargassum-laden net led to the sinking of his boat. He and his four colleagues pulled the casted net out in the open Atlantic Ocean off the Brazilian coast, realising their haul of fish was tonnes of sargassum. The weight of the net threw off the boat’s balance, leading to its capsizing. “The damage was large. We lost all our devices, the navigator, the radio, our mobile phones,” he recalls.

Fisherfolk further north in the Atlantic Ocean, toward Trinidad and Tobago, have similar experiences. Renelle Kissoon, a local government councillor for a small fishing village, recalled that between 2018 and 2023, fisherfolk who usually use the sand to push their boats off the shore would encounter significant difficulty getting their pirogues into the water. Then, if boats enter the ocean, the seaweed becomes stuck in the engine's propellers. “Engines won't just get stuck due to the Sargassum; the seaweed would even destroy them. Many fishermen would have had to replace engines and even nets", she says.

While fisherfolk suffer direct impacts on their livelihood, Renelle Kissoon explained that sargassum has notable impacts on the local tourism industry, supporting businesses, and environmental effects on the coastline.

On top of impacting the Lesser Antilles that demarks the change from the Atlantic Ocean to the Caribbean Sea, sargassum continues its path toward Central and North America, with one of its final resting places on the Mexican coastline. Biologist Rosa Rodríguez estimated that cleaning up sargassum from one kilometre of beach annually in Mexico can cost up to one million dollars. Despite the magnitude of the problem, she and other scientists agree that it is possible to adapt and turn sargassum into an opportunity, such as a raw material for producing bricks, fertilisers, and biofuels, among other things.

Read their full stories below and learn more about how sargassum unites those three countries, from the causes and consequences of the problem to the possibilities of the solution.