Sargassum is a type of floating brown algae that provides food, protection, and habitat for many marine species. While Sargassum plays an important role in the health and biodiversity of open ocean ecosystems, it can also be harmful in certain situations when rafts of this brown algae are carried to shore by winds and currents. Out at sea in U.S. waters, NOAA manages many fish species that depend upon floating mats of Sargassum for food and shelter. When Sargassum rafts are pushed to land by wind and waves, NOAA and partners provide tracking and forecasting tools to help people know when and where mats of algae are likely to come ashore. Once Sargassum washes on land, NOAA experts provide support and scientific expertise to help affected communities. Lastly, ongoing NOAA research helps us better understand and manage the public health, social, and economic issues posed by Sargassum.
Historically, the majority of Sargassum was located in the Sargasso Sea in the western North Atlantic. In 2011, the geographic range of Sargassum expanded. A newly established population, driven by shifting wind patterns, is now thriving in the open ocean. This region is called the "Great Atlantic Sargassum Belt." Massive amounts of Sargassum from this area are transported west into the Caribbean Sea, Gulf of Mexico, and tropical South Atlantic via ocean currents.
Free-floating Sargassum in the ocean provides habitat, food resources, protection, and breeding grounds for hundreds of marine species. This includes commercially important fisheries species such as gray triggerfish, amberjack, and mahi mahi that feed on the smaller marine life present in Sargassum mats. In the South Atlantic, Gulf of Mexico, and the Caribbean, NOAA designates areas of Sargassum as "Essential Fish Habitat." Juvenile sea turtles and sea birds also use Sargassum for feeding and shelter. In the South Atlantic and portions of the Gulf of Mexico, Sargassum is designated as Critical Habitat for threatened loggerhead sea turtles under the Endangered Species Act.
Sargassum inundation events occur when rafts of this algae are carried to shore by winds and currents. These events are a type of harmful algal bloom that can adversely impact coastal ecosystems, tourism, and public health. Massive amounts of Sargassum can form brown tides nearshore, smothering fauna and flora — including coral reefs. Sargassum mats may also clog water intake pipes used in critical infrastructure (for example, in desalination plants that produce drinking water). Sargassum also contains high levels of arsenic and other heavy metals, organic contaminants, and marine debris. Sargassum decomposing on the beach produces hydrogen sulfide, a gas that smells like rotten eggs, which can cause respiratory irritation. Cleanup options are limited and costly.
Several NOAA offices monitor and track Sargassum, providing online forecasts and near real-time conditions. One effort, a partnership between NOAA's Atlantic Oceanographic and Meteorological Lab and the University of South Florida, uses NOAA satellites to generate a weekly risk map that shows where Sargassum is likely to wash ashore in coastal areas of the U.S., Caribbean, and Central America. The Caribbean Coastal Ocean Observing System, a regional association of NOAA's Integrated Ocean Observing System, also monitors and tracks Sargassum in the Atlantic and Caribbean, offering short- and long-term forecasts, a seven-day outlook, and the latest satellite imagery of affected regions. Research continues to improve these products, including a 2023 study to incorporate community science reports to improve monitoring. Image credit: Marine Macroalgae Research Lab - Florida International University
NOAA designates Sargassum as Essential Fish Habitat for several species, including gray triggerfish, amberjacks, and mahi mahi. These fisheries are managed by regional fishery management councils in the South Atlantic, Gulf of Mexico, and the Caribbean. While "Essential Fish Habitat" status itself does not restrict harvest, NOAA Fisheries consultation is required for any federal activities in these areas that may impact the habitat. In a separate management plan, NOAA Fisheries prohibits harvest of Sargassum in all U.S. federal waters (between 3 miles to 200 nautical miles) south of the North Carolina/South Carolina state boundary. Sargassum is also designated as Critical Habitat for threatened loggerhead sea turtles in certain areas of the South Atlantic and Gulf of Mexico. Image credit: Florida Fish and Wildlife
When excessive amounts of Sargassum reach the shore, it is referred to as a "Sargassum inundation event," or SIE for short. Such events can become "harmful algal blooms" — when algae grows out of control or produces toxins that harm people, fish, shellfish, marine mammals, and birds. NOAA's National Centers for Coastal Ocean Science (NCCOS) coordinates cross-agency actions during such events. This office funds research to understand and manage harmful algal blooms, which includes improving detection and forecasting technologies. NCCOS also engages with people affected by Sargassum to aid in the design of more accurate and timely warnings. In addition, NCCOS is studying the social and economic impacts of Sargassum beaching. Image credit: Life on the Edge 2004
NOAA’s Office of Response and Restoration may provide scientific support for inundation events that receive a federal emergency declaration, such as the 2022 declared emergency in the U.S. Virgin Islands. Experts in this office are also studying and preparing for responding to oil and chemical spills that involve Sargassum. In addition, NOAA's Office for Coastal Management provides expertise and training to communities to address coastal issues with the goal to increase the resilience of the nation's coastal zone. Image credit: NOAA
The top two lines of this infographic say "Sargassum: from sea to shore" and "What is Sargassum, where does it come from, and what happens when it washes ashore?" Underneath this text, there is an illustration that shows Sargassum, a brown and orange-tinted algae, in the open ocean on the far left, within the U.S. federal waters in the middle, and a coastal Sargassum inundation event (beaching) on the right. The illustration is three-dimensional, showing the surface of the ocean and land, as well as a cross section of the ocean below. The bottom right of this graphic shows the NOAA logo and a note that says "This diagram is not drawn to scale and is meant for illustrative purposes only." The following are descriptions of each of the three sections of this illustration: