Sargassum es un tipo de alga parda flotante, comúnmente llamada "alga marina". Estas algas flotan en la superficie del mar, nunca se adhieren al fondo marino, y pueden agregarse para formar grandes esteras en mar abierto.

Historically, the majority of Sargassum aggregated in the Sargasso Sea in the western North Atlantic, with some small amounts found within the Gulf of America and Caribbean Sea. In 2011, the geographic range expanded, and massive amounts of Sargassum moved west into the Caribbean Sea, Gulf of America, and tropical Atlantic, washing ashore in Florida, Puerto Rico, the US Virgin Islands, and most islands and coastal areas in the Caribbean Sea and Western Africa.

Esta infografía ilustra el movimiento del sargazo del mar a la costa. En el mar , el sargazo constituye un importante hábitat para los peces y la fauna. Sin embargo, esta alga flotante a menudo llega a la costa en grandes cantidades debido a los fuertes vientos y corrientes de agua. La llegada masiva de estas algas a la costa puede dañar los ecosistemas costeros, ahuyentar a los turistas y suponer una amenaza para la salud pública. La NOAA está trabajando para ayudar a las comunidades costeras a hacer frente al creciente problema de lo que los expertos llaman "eventos de inundación de Sargassum." Crédito de la imagen: NOAA National Ocean Service

Researchers are still assessing various hypotheses about the cause of this first documented extreme event. One hypothesis proposes that during the winter of 2009–2010, the winds that typically blow to the east, from the Americas to Europe, strengthened and shifted to the south more dramatically and persistently than any other time in the 1900–2020 record. This shift in winds triggered a long-distance eastward dispersal of Sargassum, from the Sargasso Sea, toward the Iberian Peninsula in Europe and West Africa.  After exiting the Sargasso Sea, the Sargassum drifted southward in the Canary Current and entered the tropics. Once in this new and favorable tropical Atlantic habitat, with ample sunlight, warm waters, and nutrient availability, the Sargassum flourished and has continued to grow. 

In addition to changing wind patterns, other hypotheses include a combination of factors, such as nutrient inputs from major rivers (e.g. Amazon and Orinoco) and Saharan dust (adding phosphorus and iron to the ocean), coastal upwelling, and warmer sea surface temperatures that promote Sargassum growth.

Having established a new population, the Sargassum now aggregates almost every year, starting in January/February in a massive windrow or “belt” north of the Equator, along the region where the trade winds converge. During the late winter and early spring months, the Sargassum moves northward with the seasonal winds and currents. By June, this belt may stretch across the entire central tropical Atlantic. Large portions of this algae are then transported into the Caribbean Sea and Gulf of America via the North Equatorial Current and Caribbean current systems.

Since 2011, large accumulations of Sargassum have occurred every year in the Caribbean Sea, Gulf of America, and tropical Atlantic, but the amount can vary from year to year.

The presence of Sargassum occurs over large areas from the tropical Atlantic in the east, to the Gulf of America in the west, approximately 5,000 kilometers from the eastern tropical Atlantic to the west off the Mexican coast in the Caribbean Sea.  Sargassum does not extend as a blanket (or blob) covering the full surface of the ocean in these regions. Instead, Sargassum floats in patches that range in size from a few centimeters to hundreds of meters. Some of these patches reach the coastal areas, including beaches, ports, and even intake systems for drinking water.  The area that these patches cover has been significantly larger in recent years than prior to 2011.  

Satellite sensors can estimate indicators related to Sargassum coverage, which enable us to quantify the area affected and estimate the volume of Sargassum in a specific region.

Sargazoen cantidades normales, proporciona hábitat, alimento, protección y zonas de reproducción a cientos de especies marinas diversas, incluidas especies de importancia comercial, como el atún y el pez espada, que se alimentan de la vida marina más pequeña presente en el Sargazo Sargassum. Si Sargassum llega a la costa en cantidades pequeñas/normales, puede ayudar a evitar la erosión de las playas.

Out at sea, Sargassum is an important habitat for fish, sea turtles, and other marine organisms, but as it accumulates close to the coastlines it can smother valuable corals, seagrass beds, and beaches. As it washes ashore the seaweed begins to decay, attracting flies and other insects. Additionally, during its breakdown, Sargassum produces hydrogen sulfide gas, which smells of rotten eggs, repelling beachgoers and affecting the tourism industry that depends on pristine ocean conditions. Sargassum can also impact navigation, block water intake in desalination plants, and impact benthic ecosystems after/if they sink to the bottom of the ocean.

Studies of the impact of Sargassum on human health started very recently and this is a topic that needs more time to be fully understood. However, when decomposed, Sargassum releases hydrogen sulfide (a gas) that may cause respiratory health problems. Sargassum is also known to often contain heavy metals that can be toxic to humans and animals. In addition, recent studies have found that Sargassum mats can harbor pathogenic Vibrio bacteria, which can lead to skin infections or gastrointestinal illness from direct contact or consumption of contaminated seafood, particularly in vulnerable individuals.

The experimental Sargassum Inundation Report (SIR) provides an overview of the area of current Sargassum patches and the risk of Sargassum inundation in coastal regions of the Caribbean, tropical Atlantic, and Gulf of America. SIR is an experimental product that updates on a weekly basis and uses satellite-based data to estimate the potential for Sargassum to wash ashore.   It is not a forecast.

SIR muestra las condiciones actuales de Sargazo e identifica las zonas costeras donde el Sargassum se encuentra en un radio de 50 km (30 millas) y, por tanto, pueden verse afectadas por el Sargazo en los días/semanas siguientes. La incidencia real de la inundación costera dependerá en gran medida de las condiciones locales de corriente, marea, viento y oleaje. El potencial de inundación se clasifica entonces en tres niveles: bajo, medio y alto, que se basan en gran medida en la distancia entre las manchas de Sargazo a la costa, y la densidad y extensión de estos parches. Las líneas costeras se codifican por colores en función de estos tres niveles.

SIR sirve como fuente de información sobre la distribución actual de Sargassum en distintas zonas, su potencial para llegar a la costa, y puede utilizarse para hacer un seguimiento de los movimientos pasados de Sargassum en la región, lo que puede permitir a los investigadores formular hipótesis sobre la evolución del riesgo en el tiempo.

Los investigadores están utilizando imágenes de satélite para identificar las zonas de mar abierto donde el Sargassum y calculan dónde pueden producirse varamientos en función de la densidad y la proximidad del Sargassum de la costa. Aunque no se trata de un pronóstico, ayuda a las comunidades a prepararse para posibles inundaciones. Los investigadores utilizan sus conocimientos sobre las corrientes oceánicas, los vientos y las condiciones del oleaje para mejorar estas estimaciones.

Identificación de Sargassum desde el espacio es compleja. Sargassum puede observarse indirectamente por satélite desde el espacio midiendo cómo se refleja la luz en la superficie del océano.

El AOML está llevando a cabo una investigación para evaluar el impacto de las corrientes oceánicas, los vientos y las olas en la distribución y trayectoria del Sargassumcon el fin de aumentar la precisión de Sargazo Sargassum. También realizamos un seguimiento como parte del Nodo del Caribe de NOAA NESDIS CoastWatch alojado en el AOML: https://cwcgom.aoml.noaa.gov/cgom/OceanViewer/

Currently SIRs are created from a satellite-derived quantity (density of Sargassum), which is estimated by the University of South Florida using data from multiple satellite sensors, including NASA MODIS (Moderate Resolution Imaging Spectroradiometer) sensor onboard the NASA Aqua and Terra satellites, NOAA/NAS VIIRS (Visible Infrared Imaging Radiometer Suite) onboard Suomi-NPP and NOAA-20/21 satellites, and ESA OLCI (OCean and Land Colour Instrument) onboard Sentinel-3A and Sentinel-3B.  . 

To improve detection in coastal waters, NOAA CoastWatch, AOML and USF are planning to integrate high resolution data from the MSI (Multispectral Instrument) onboard Sentinel-2A and Sentinel-2B satellites. This effort will improve the coverage and detail in coastal regions, which are challenging to monitor with moderate resolution sensors.

The estimates provided by the SIR have been validated in different areas of the Caribbean Sea and tropical Atlantic Ocean. The results of this validation were published in Aquatic Botany (Elsevier) in 2024 here. 

An international citizen science effort to collect mostly coastal observations of Sargassum is led by Florida International University, through the Epicollect Sargassum Watch web pages.  Epicollect is a mobile and web application to collect science data.   NESDIS CoastWatch and AOML contribute to this effort through its Sargassum citizen science web page located here.

El movimiento, la extensión y la densidad del Sargassum es muy complejo: crece, se hunde y se desplaza en función de las corrientes oceánicas, los vientos y las olas. Por ello, a veces no es posible describir trayectorias de antemano, sino una descripción general de cómo han cambiado la extensión y la densidad medias. Proyectar una trayectoria precisa del Sargazo es un reto y un área actual de intensa investigación. Por el momento, no es posible predecir el momento de la varada del Sargassum.

There are two main sources of Sargassum reaching the Gulf of America, one is local and peaks in April-May, and the second one is the Caribbean Sea which peaks during the summer months.

Large amounts of Sargassum are currently located in the Caribbean Sea, moving towards the Yucatan Peninsula, and spreading through the Gulf of America by the Loop Current.  

The Loop Current flows through the Florida Straits and off the east Florida coast, where it is known as the Florida Current, and into the Gulf Stream as it heads north up the eastern coast of the US.  The very strong Loop Current is now transporting moderate amounts of Sargassum that were previously located in the Caribbean Sea, with larger amounts potentially on the way.   Some of the Sargassum in the Gulf of America also originates locally.  Whether the Sargassum will beach on the coast of Florida, including the Florida Keys, will largely depend on the local wind, wave, and tide conditions.  Given the complexity of its motion and temperature-dependent growth and decay, it is not possible to forecast the timing of beaching.  However, given the size and number of the current Sargassum patches, there is a strong chance that Sargassum carried by the Florida Current may reach the Florida coast despite wind and wave conditions. As of May 2025, satellite observations indicate that some of this Sargassum has already been observed along the Florida Keys.

Maps showing Sargassum patches for the week of June 3-9, 2025 as derived from satellite images and reported weekly through the AOML experimental Sargassum Inundation Report. To view the most recent report, click this link.

Sargassum outlooks are published once a month by the University of South Florida. These outlooks show maps with the monthly (past month) extensions of Sargassum.  The current (April 2025) total extension of Sargassum in the tropics is 40% higher than the all-time high in June 2022, which makes 2025 a new record year, with large extensions of Sargassum observed in the Caribbean Sea since February. While this Sargassum remains at the sea surface and moves with help from ocean currents, winds, and waves, it may grow and increase its density, provided that it encounters warm temperatures and plenty of nutrients.  If the large amount of Sargassum that is presently in the Caribbean Sea remains at the surface, it has the potential to spread more widely throughout the Gulf of America and then by the Loop Current and Florida Current (the name of the Gulf Stream off Florida) to reach the Florida Keys and the east Florida coast and Bahamas.  

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Miron, P., M.J. Olascoaga, F.J. Beron-Vera, N.F. Putman, J. Trinanes, R. Lumpkin y G.J. Goni. Clustering of marine debris- and Sargassum-like drifters explained by inertial particle dynamics. (2020). Geophysical Research Letters, 47(19):e2020GL089874, https://doi.org/10.1029/2020GL089874.

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