The potential presence of up to 40 million tons of sargassum seaweed spread across the Atlantic Ocean paints a particularly delicate picture for the coming months. Although the media spotlight is on the Caribbean, this phenomenon has implications that extend throughout the North Atlantic , including the European coast, where influxes of macroalgae have already been recorded in recent years in Portugal, the Canary Islands, and some areas of the French Atlantic coast.
Figures released by the National Laboratory for Earth Observation (LANOT) of the National Autonomous University of Mexico (UNAM) indicate an unprecedented volume of biomass. This floating macroalga, which forms a valuable ecosystem in the open ocean, becomes a complex problem when it reaches the coasts: it damages beaches, compromises reefs and seagrass beds, and generates millions of dollars in losses for tourist destinations—a situation that worries both the Mexican Caribbean and Atlantic coastal regions in the Americas and Europe.
A saturated Atlantic: the largest sargassum belt ever recorded
LANOT specialists anticipate that the tropical Atlantic could accumulate nearly 40 million metric tons of sargassum this year. This immense band of floating seaweed is known as the Great Atlantic Sargassum Belt , a kind of biological highway that shifts toward the Caribbean each season, driven by currents and winds.
The increase is not isolated: since 2022, there has been a notable jump in the amount of sargassum reaching the coasts , particularly in the Mexican state of Quintana Roo . In 2025, approximately 96.000 tons of sargassum were removed from that area, and forecasts for this year raise the potential figure on Quintana Roo's beaches to 130.000 tons , which would make it one of the worst episodes on record.
This behavior is closely linked to large-scale changes in the ocean: warming waters due to climate change , the increased input of nutrients (partly from large rivers and human activities), and altered ocean currents and wind patterns. Together, these factors have created ideal conditions for sargassum to proliferate rapidly and travel great distances.
Scientists point out that this macroalga can double its volume in just 18 days under certain circumstances. This explosive growth, combined with the dynamics of Atlantic currents, explains how a mass originating far out at sea can end up affecting coastlines as far apart as the Caribbean or certain stretches of the European Atlantic in a matter of weeks.
In practice, this means that European countries with an Atlantic coastline—from Portugal and Spain (especially the Canary Islands) to France and Ireland—are obliged to closely monitor what is happening downstream in the tropical Atlantic. Although the most severe impacts are concentrated in the Caribbean, recent experience with strandings of macroalgae and jellyfish on the European coast demonstrates that large-scale ocean phenomena know no borders.
The Mexican Caribbean as a laboratory for what can happen on other coasts
Although the problem originates in the Atlantic, the Mexican Caribbean has become a veritable open-air laboratory for managing sargassum influxes. In places like Quintana Roo, the phenomenon manifests itself with enormous spatial variation : in some stretches of coastline the impact is moderate, while in others the beaches are literally buried under mounds of seaweed.
Recent reports from UNAM, based on satellite monitoring and fieldwork , reveal a highly uneven picture. A bulletin indicated that, of 100 beaches analyzed in northern Quintana Roo, 17 were classified as having excessive sargassum accumulation, another 17 as having abundant sargassum, 25 as having moderate accumulation, and only three beaches showed no presence of the macroalgae. This type of rapid assessment is crucial for allocating resources where they are most needed.
Daily management is complex. Municipalities and tourism companies have had to reinforce mechanical and manual cleaning , organize almost permanent removal teams, and set up areas for land-based disposal. However, these emergency measures do not solve the underlying problem and, moreover, generate other environmental complications that are beginning to raise alarms in other Atlantic countries with a heavy reliance on tourism.
For Spain and the rest of Europe, what is happening in the Caribbean offers a roadmap of risks and solutions . Both the Spanish Mediterranean coast—highly sensitive to the image of its beaches—and Atlantic enclaves like the Canary Islands and Madeira are closely observing how action protocols are structured, how coordination between administrations is achieved, and how the tourism sector is involved, in case it becomes necessary to replicate some of these strategies in the face of severe macroalgae blooms or other similar events.
In this context, estimates of up to 40 million tons of sargassum in the Atlantic are not only a shocking figure, but a warning that managing large volumes of marine biomass could become a recurring task for many ocean coasts, from Mexico to the Iberian Peninsula.
Environmental, economic and health impacts
Sargassum, under natural conditions, is a valuable floating habitat : it provides refuge for fish, crustaceans, sea turtles , and other species that find food and protection among its fronds. However, when these enormous masses wash ashore, this same ecological resource becomes a source of stress for coastal ecosystems.
On beaches and in shallow areas, the accumulation of algae reduces the amount of light entering the water , resulting in decreased photosynthesis by seagrasses and corals. This prolonged shading damages coral reefs , which are essential for biodiversity and provide natural protection against storms and waves. The degradation of these reef ecosystems is a shared concern in regions such as the Canary Islands, the Azores, and Madeira, where corals and benthic communities play a key role in coastal stability.
Another problem arises when the sargassum enters a phase of mass decomposition. During this process, unpleasant odors, gases, and leachate are released , which can diminish the attractiveness of the beaches and cause discomfort to residents and visitors. Furthermore, some of the biomass sinks, escaping the containment barriers and creating what is known as "brown tide ," a band of murky water that affects both marine life and recreational users.
Studies led by LANOT and other Mexican institutions indicate that these algae have the capacity to absorb heavy metals present in the sea, such as arsenic, mercury, and cadmium. This makes sargassum, once stranded, unsuitable as livestock feed and, if deposited uncontrollably in the jungle or on permeable soils, poses a risk of aquifer contamination . In regions with karst systems—which are highly porous—such as the Caribbean and certain stretches of the European Atlantic coast, this issue is particularly critical.
Intensive mechanical beach removal is not without its drawbacks. The use of heavy machinery on the sand can end up dragging sediments and accelerating beach erosion. In areas where artificial coastal regeneration already represents a constant expense—as is the case in many Spanish tourist municipalities—this type of additional erosion would translate into higher costs in the medium term.
Finally, the economic impact is particularly noticeable in destinations that depend on sun and sand. The persistent presence of seaweed blooms, unpleasant odors, and murky water causes some tourists to change their destination or shorten their stay—a trend already observed in the Mexican Caribbean that could be replicated in other locations if effective measures are not taken.
How sargassum is monitored: from satellite to drone via GPS
Given such a dynamic phenomenon, the key is knowing where the sargassum is, how much there is, and where it is headed . UNAM, through LANOT and in collaboration with the Institute of Marine Sciences and Limnology, has developed a monitoring system over the last six years that combines various technologies and can serve as a reference for other Atlantic regions, including Europe.
The first pillar of this system is satellite imagery , including that provided by the European Sentinel-2 satellite, which is freely accessible. These images, updated approximately every five days, allow for the detection of sargassum patches in the open ocean and the estimation of their extent. Based on the algae's spectral signature—its particular response to light at different wavelengths—it is possible to distinguish sargassum from other elements on the sea surface.
To refine these calculations, the scientific team uses floating GPS devices that are left adrift near the algae blooms. These devices transmit their position in real time, helping to track the exact trajectory of the blooms. In turn, the use of spectroradiometers in the field allows them to verify that what is observed from space corresponds to reality in the water, thus completing the cycle between satellite data and direct observation.
Drones have become a very useful complementary tool for inspecting specific sections of reef and coastline in great detail. They allow for the documentation of how sargassum, waves, and coastal ecosystems interact, and for the precise evaluation of the condition of containment barriers and the effectiveness of cleanup efforts.
All this information is fed into a web viewer developed by LANOT, which integrates historical images, position data, and drift models. This platform makes it easy to see how far away the large slicks are, how much biomass might arrive, and in which areas they are most likely to strand. The accumulated archive already exceeds 4.700 images of the study region, allowing for retrospective analysis to better understand the evolution of the phenomenon and refine predictive models.
Models and strategies: anticipating before the sargassum reaches the shore
Beyond simply observing what is happening at any given moment, scientists work with oceanographic and atmospheric models that combine information on currents, winds, and waves. These models allow them to fill in the gaps between satellite passes and project the future movement of oil slicks, providing coastal authorities with crucial flexibility.
In practice, these models allow for forecasting arrival times several days in advance. With early warning, municipalities can increase cleaning staff, reinforce barriers at strategic points, or even plan offshore harvesting operations before the seaweed reaches the shore. This approach, already being tested in the Caribbean, is of great interest to any region that wants to minimize the visual and ecological impact on the most fragile part of the coastline.
One strategy gaining traction involves intercepting sargassum seaweed offshore, shredding it, and processing it to prevent it from reaching the beaches. This reduces the burden on coastal ecosystems and opens the door to potential industrial uses of the biomass, provided that the heavy metals accumulated in the algae are carefully managed.
In parallel, efforts have focused on installing containment barriers along the coast. In Quintana Roo, some 90 kilometers of these floating structures have been deployed, designed to retain the sargassum and channel it to collection points. However, experience shows that when the quantities are very large and the sea is rough, a portion of the seaweed sinks, passes under the barriers, and ends up spreading as a brown tide.
This type of hybrid solution—barriers, offshore harvesting, and improved early warning systems—is also beginning to be discussed among European coastal managers and scientists. As events associated with global warming intensify, transatlantic cooperation in monitoring and responding to large macroalgal blooms is likely to become increasingly necessary.
The fundamental challenge lies in finding a balance between protecting the ocean ecosystem , maintaining environmental quality on beaches, and ensuring the economic viability of sectors that depend on tourism and maritime activities. What is being tested today in the Caribbean could, with appropriate adaptations, serve as a reference for future strategies on the Atlantic coasts of Europe and North Africa.
Faced with an Atlantic Ocean that could carry tens of millions of tons of sargassum, the combination of cutting-edge science, planning, and international coordination is emerging as the most robust tool to ensure that the impact on coastlines—from Mexico to Spain—is as manageable as possible, keeping both ecological damage and economic and social consequences at bay.
