Sentinel-2 satellite. Image credit:
ESA/ATG medialab
This year is expected to see a record-breaking amount of Sargassum biomass in the Atlantic Ocean according to forecasts from the Mexico based National Earth Observation Laboratory (LANOT), who estimate that 40 million tonnes of the biomass will be circulating in 2026.
Sargassum biomass refers to the accumulation of floating brown macroalgae (seaweed) in the Sargassum genus, which drifts on the ocean surface in vast mats and can swamp coastlines causing both economic and environmental damage. Blooms can grow quickly and have been known to double in volume in less than three weeks. Mexico sees such blooms make landfall and last year Quintana Roo, a Mexican state on the Yucatán Peninsula’s eastern coast, saw around 90,000 tonnes arrive according to researchers from LANOT. Given that the Quintana Roo area is a tourist destination known for beaches and resorts, the challenges of having thousands of tonnes of Sargassum arrive is obvious.
At a recent ‘Sargassum Detection in the Mexican Caribbean Using Satellite Imagery’ conference, LANOT described how their specialised tool, that has been operating for six years, uses Sentinel-2 imagery to provide interactive maps for tracking Sargassum. A mosaic of 18 images is generated every five days with algorithms providing processing to apply as atmospheric correction, cloud masks, land and beach masks, using bands 4, 8, 8A, and 11.
The satellite imagery is complimented with ocean current, wind, and wave models together with floating GPS devices to enable the tool to predict the arrival of blooms at the coast. A spectroradiometer is used gather the spectral signatures of the algae, and drones are used to observe what is happening on the reefs. All this data is analysed and visualised in an online viewer, which can be found here, to enable users to assess the location and volume of Sargassum and where it is likely to make landfall. The tool covers the Mexican Caribbean area including Quintana Roo and extends to Belize, Honduras, and Guatemala; updated every five days.
Although containment barriers have been installed at points along the Mexican coastline, they are being overwhelmed by the amount of Sargassum arriving. In addition, when the Sargassum decomposes it creates what is described as a ‘brown tide’ on the shoreline which depletes water oxygen and releases toxic gases.
Economic losses can be significant with tourist businesses in Quintana Roo reporting a 50% reduction in revenue when the blooms make landfall as visitors go elsewhere, and the large volumes can impede maritime traffic including tour boats and fishermen. While environmentally, the beach cleaning efforts themselves can cause coastal erosion as sand is scraped up with the Sargassum.
Of course, Mexico is not the only place in the world that suffers from Sargassum blooms. There are other satellite-based tools to help researchers and users track them. For example:
- NOAA’s Sargassum Inundation Risk tool provides a daily report with a ground resolution of approximately one kilometre along coastal areas in the Caribbean, Florida, Gulf of America, and northern South America. This can be used by the public, fishermen, and communities to anticipate impacts and take mitigation measures.
- Copernicus Marine Service released a Sargassum detection product at the end of 2025 providing near real-time monitoring of floating sargassum across the Atlantic and Caribbean basins. This tool uses data from Sentinel-2, Sentinel-3, MODIS (both Aqua and Terra), Landsat, and GOES satellites to provide measurements at ground resolutions of between 20 metres and one kilometre.
Summary
Changes in the climate seem to have enhanced the volume of Sargassum in the oceans, and this year it is reported that the season has started earlier than normal. Due to the economic, environmental and potential health impacts, tools monitoring the growth, location and movement of such blooms are vital to help individuals, business, and communities to monitor and mitigate them with satellite observations being a key part of the solution.
