Since 2011, summer scenes of sargassum on beaches in South Florida and throughout the Caribbean have become common. The seaweed, which takes its name from the Portuguese word 'sargaço' meaning grape, was documented by Christopher Columbus during his voyage to the Americas. Portuguese navigators originally identified the small, grapelike, air-filled bladders that keep the algae afloat in the Sargasso Sea region.
In winter 2010, strong winds brought sargassum from the Sargasso Sea to the tropical Atlantic. For a few years after 2010, strong winds in winter and spring mixed deeper, nutrient-rich water to the surface, enabling sargassum blooms. In 2011, people began noticing unusually large mats of sargassum in the tropical Atlantic between the coasts of Africa and Brazil.
A Self-Sustaining Cycle
Researchers suggest that the main cause of the sargassum blooms in the Great Atlantic Sargassum Belt has changed. Scientists explored causes including changes in nitrogen and phosphorus from the Amazon and Congo river basins, Saharan dust, and ocean temperatures, winds and currents, but none fully explained year-to-year variations. Researchers created a mathematical model that reproduced sargassum blooms from 2011 to 2022 and predicted blooms in 2023 and 2024. They used measurements of nitrogen content and isotopic composition in sargassum collected around the US Virgin Islands to validate their model.
A floating sargassum mat, home to fish, shrimp, crabs and tiny organisms, is an ecosystem called the 'sargassumsphere'. Animals in this sphere collect food and recycle nutrients through waste and breakdown of older sargassum, concentrating nutrients and helping subsequent blooms. Researchers suggest sargassum may have entered a self-sustaining cycle, effectively feeding their own expansion. Consequently, researchers suggest the Great Atlantic Sargassum Belt is likely here to stay.
The amount of sargassum in the Great Atlantic Sargassum Belt surpassed an estimated 37,500 metric tons in 2025. Forecasts suggest summer 2026 could break records for sargassum blooms. Brian Barnes, research assistant professor at the College of Marine Science at the University of South Florida, attributes the increase to warmer temperatures.
Impact on Mexico’s Caribbean Coast
A record-breaking surge of sargassum is inundating Mexico's Caribbean coastline, leading to beach closures in premier tourist destinations. The unprecedented mass of sargassum has prompted the Mexican federal government to devise an emergency response plan. In recent weeks, dozens of Quintana Roo beaches have been placed on red alert for sargassum, with some forced to close entirely. By late June, a local monitoring network reported that 92.5% of Quintana Roo's beaches registered an 'excessive' level of sargassum.
Tulum Councilman Eugenio Barbachano said the low season is not just low, it is critical. Environmental officials in Quintana Roo anticipate 119,000 tons of sargassum will wash ashore by year's end. This forecast surpasses last year's record of 96,000 tons.
Managing sargassum costs Quintana Roo roughly 11% of its tourism sector GDP, or about $2 billion annually. The Riviera Maya hotel association estimates the cost of combating sargassum at roughly $150 million annually. The Mexican Navy has deployed 11 specialized coastal ships, an amphibious sargassum collector, 18 support boats, two barges, four drones, and over 9,000 meters of containment barriers. The Mexican government is expected to unveil a revised sargassum response plan on July 30.
Health Risks and Environmental Damage
Sargassum can clog harbors, interfere with fishing and boating, harm marine life, and release gases including hydrogen sulfide, ammonia, and methane. Once stranded, sargassum rapidly decomposes, emitting a stench often likened to rotten eggs. Decomposing seaweed deprives underwater plant life of sunlight, diminishing biodiversity. It can also leach arsenic and other heavy metals into the sand.
Workers who cleared sargassum have reported itchy and burning skin, headaches, fatigue, and nausea, symptoms linked to the algae according to a 2025 study. Despite the conditions, some tourists remain undeterred. Swedish tourist Wendy said she went swimming today and expected worse.
Potential Uses and Future Solutions
Sargassum is rich in organic matter, potassium, calcium, magnesium and trace elements. After careful processing to remove salt and excessive metals, it can be used to improve soil structure, enhance water retention and stimulate plant growth. Barbados encourages farms to use sargassum as a fertilizer and soil amendment. Sargassum biomass can be used for biofuel production including bioethanol, biogas, bio-oil, and hydrogen. It does not need land, freshwater or fertilizers for biofuel production, reducing competition with food.
Scientists at a university in Barbados developed a way to produce biofuel from sargassum and wastewater from the local rum industry. Sargassum can be converted into bioethanol, biogas, bio-oil, or hydrogen via fermentation, anaerobic digestion, hydrothermal liquefaction, and gasification. It is also explored as a sustainable construction material in Mexico and Brazil. This includes compressed panels developed by researchers at the National Autonomous University of Mexico and low-cost bricks developed by Omar Vázquez Sánchez using about 40% sargassum. Using sargassum as a mortar additive helps reduce dependence on conventional, carbon-intensive materials.
Brian Lapointe, research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute, suggests the Caribbean needs a system connecting satellite observations and modeling forecasts with targeted intervention before sargassum reaches the beach.