Floating golden forests are vital to marine life but can become a coastal hazard

Nature · Published 3 October 2026 Swipe more like this →

In short: Sargassum, a drifting brown algae, serves as a crucial nursery for sea turtles and fish in the open ocean. Yet, when wind and currents push these massive mats toward land, they create inundation events that threaten coastal ecosystems, clog infrastructure, and release pungent, irritating gases as they decompose on beaches.

Historically concentrated in the Sargasso Sea, Sargassum is a genus of brown macroalgae known for its air-filled bladders that keep it buoyant. While some species are attached to reefs, others are holopelagic, meaning they spend their entire life cycle floating. In 2011, a significant shift occurred when a new population began thriving in the Great Atlantic Sargassum Belt, a vast region stretching across the open ocean, driven by changing wind patterns.

These floating mats are essential to marine biodiversity. They provide food, shelter, and breeding grounds for hundreds of species, including mahi mahi, amberjack, and juvenile sea turtles. In U.S. waters, NOAA designates these areas as Essential Fish Habitat and critical habitat under the Endangered Species Act. Because of this importance, federal agencies must consult with NOAA before authorizing activities that might impact these habitats, and the harvest of Sargassum is prohibited in U.S. federal waters south of the North Carolina/South Carolina border.

The challenge arises during inundation events, where massive quantities of algae wash ashore. These events can smother coral reefs and seagrass meadows, while the decomposition process releases hydrogen sulfide, a gas that smells like rotten eggs and causes respiratory irritation. Furthermore, the algae can contain heavy metals like arsenic. To manage these risks, NOAA partners with the University of South Florida to track the algae using satellite imagery, providing daily risk maps and forecasts to help coastal communities prepare for potential beaching events.

Managing the balance between protecting this vital habitat and mitigating its impact on human infrastructure—such as desalination plants—remains a priority. As research continues, experts are working to improve detection technologies and understand the broader social and economic consequences of these massive algal blooms, which have become a recurring feature of modern Atlantic oceanography.

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