A 5,000-Mile-Wide Seaweed Bloom Could Harm Florida’s Beaches

The Great Atlantic Sargassum Belt, a bloom of brown seaweed large enough to be visible from space, is reportedly headed toward North America—and could soon wreak havoc on Florida and Mexico’s beaches.

Scientists said that this bloom is one of the largest ever recorded, measuring approximately 5,000 miles wide; in comparison, the continental U.S. is approx 3,000 miles wide. When out in open water, seaweed blooms like this are typically harmless. They can even be beneficial by absorbing carbon dioxide and serving as a habitat for marine life. However, due to this bloom’s size, some are concerned that it could damage coastal ecosystems should it get close to shore.

“Even if it’s just out in coastal waters, it can block intake valves for things like power plants or desalination plants, marinas can get completely inundated and boats can’t navigate through,” Brian Barnes, an assistant research professor at the University of South Florida’s College of Marine Science told NBC News. “It can really threaten critical infrastructure.”

As sargassum rots, it releases hydrogen sulfide, which can reduce water quality and create respiratory problems in humans.

“Following the big 2018 blooms, doctors in Martinique and Guadeloupe reported thousands of people going to clinics with breathing complications from the air that was coming off these rotting piles of sargassum,” Brian LaPointe, a research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute told NBC News. “What we’re seeing in the satellite imagery does not bode well for a clean beach year.”

In addition to environmental and health concerns, many worry that the seaweed-covered beaches will be expensive to remove and deter tourism.

Barnes said that this seaweed bloom seems to grow in size each year, with 2018 and 2022 having had the largest accumulations, though this year’s bloom isn’t far behind. A 2019 study suggested that human activity and the climate crisis have greatly exacerbated this bloom’s growth rate.

“You have the Congo, the Amazon, the Orinoco, the Mississippi — the largest rivers on the planet, which have been affected by things like deforestation, increasing fertilizer use and burning biomass,” LaPointe said. “All of that is increasing the nitrogen concentrations in these rivers and so we’re now seeing these blooms as kind of a manifestation of the changing nutrient cycles on our planet.”