In the Caribbean, large-scale accumulations of Sargassum algae continue to grow, while in the Sargasso Sea itself, from which these algae get their name, their biomass, on the contrary, is noticeably decreasing. New scientific data shows that the distribution of sargassum in the Atlantic no longer follows a familiar and stable pattern.
Since 2011, the so-called Great Atlantic Sargassum Algae Belt has formed in the tropical Atlantic Ocean — an extended strip of floating macroalgae from the coast of West Africa to the Caribbean Sea. It is this belt that today is the main source of massive releases of sargassum onto the shores of the Caribbean region, including Mexico. At the same time, in the northern part of the Sargasso Sea, which for decades was considered the main natural reservoir of these algae, a steady decrease in their biomass has been recorded since 2015.
This contrast explains why Caribbean powers continue to experience regular episodes of sargassum contamination on their coasts, even as its numbers decline overall in the North Atlantic. And this year, algae appeared on the beaches even earlier than usual.
The key scientific explanation for what was happening was an article published on November 5, 2025 in the journal Nature Geoscience. It analyzes the evolution of biological nitrogen fixation processes in the Atlantic over the past 120 years. The authors concluded that large-scale Sargassum algae blooms after 2011 are directly related to the rise of phosphorus-rich deep waters in the equatorial Atlantic.
Excess phosphorus stimulates microorganisms associated with Sargassum to fix atmospheric nitrogen, which opens the way for the algae to grow actively even in nutrient-poor waters of the open ocean. At the same time, the researchers emphasize that the source of phosphorus — not river runoff or local pollution, as previously thought, but natural ocean circulation throughout the entire Atlantic basin. The further dynamics of Sargassum algae, according to the authors, will depend on how global warming affects these equatorial processes.
The second article, also published on December 4, 2025 in Nature Geoscience, documents a sharp decline in sargassum in the northern Sargasso Sea since 2015. Possible causes include rising sea surface temperatures.
These findings are supported by satellite monitoring data from the University of South Florida's Optical Oceanography Laboratory. The December 2025 bulletin, published in January 2026, noted significant increases in sargassum seaweed in nearly all Atlantic regions, particularly in the eastern Caribbean and western Atlantic, which recorded record levels for December. The 2026 forecast indicates a high likelihood of continued elevated sargassum concentrations in the Caribbean Sea with extremely low levels in the Gulf of Mexico.
In 2026, the sargassum season in the Mexican state of Quintana Roo began in January, and not traditionally in April-May, as it was before. The first significant emissions were recorded on beaches from Cozumel to Tulum, Puerto Morelos and Playa del Carmen, which was an unusual occurrence for the beginning of the year.
The previous 2025 season was historically strong, with more than 91,000 tons of sargassum collected from the beaches of Mexico's Caribbean coast from April to October, up 147% from 2024's approximately 37,000 tons. This concentration was one of the highest in recent years and required large-scale beach clean-up work.
For Mexico, the conclusion is clear: the country will continue to face regular releases of sargassum algae onto the beaches of the Caribbean coast. Modern research clearly shows that this is not a local problem, but a consequence of large-scale oceanic and climatic processes. Sargassum accumulation episodes will recur annually and probably more frequently than in previous years.