Record-Breaking Sargassum Seaweed Blob Moving Toward FL, Researchers Say

FLORIDA — A record-setting sargassum seaweed blob is moving across the eastern Caribbean Sea and west Atlantic toward south Florida, research from the University of South Florida’s Optical Oceanography Laboratory shows.

Total amounts of seaweed in these areas “reached surprisingly high levels” in April - about 200 percent higher than the same month in previous years on record. Data on sargassum blooms has been collected by USF since 2011.

“Over the last month, we saw somewhere around 31 million metric tons of sargassum, which is the highest amount we’ve ever recorded in this area and would be the largest macroalgae bloom ever,” Dr. Brian Barnes with USF’s College of Marine Sciences told News 6.

The complete seaweed belt stretches more than 5,000 miles from the Atlantic right off the coast of Africa into the Gulf.

Thick mats of seaweed have already been reported washing up on beaches around the Caribbean and along Florida’s southeast coast.

While other parts of the Caribbean, the Atlantic and the Gulf showed an average amount of seaweed, the total amount in all regions combined was 150 percent higher than the historical record in April, USF researchers said.

This total was 40 percent higher than the all-time high ever recorded in June 2022. This “makes 2025 a new record year,” according to the report.

“Most of these increases are due to both local growth and physical transport, but the exact reasons behind these new historical records need to be investigated,” USF said.

The amount of seaweed is expected to continue to increase in most regions of the Caribbean, the Gulf and the Atlantic.

"Why exactly we have all of a sudden this much sargassum? It's still being investigated, but our speculation is the ocean is warmer than usual in April and March. Also, the wind is stronger than previous years. That will stir up the ocean water," Dr. Chuanmin Hu with USF told Fox 13.

Seaweed masses will also continue to wash ashore in most of the Caribbean nations and islands and along south Florida.

This seaweed is “critically important to preserving the health and well-being of the beach ecosystem,” the city of Cape Canaveral wrote in a Facebook post earlier this month.

The city added, “It can help anchor dunes by trapping and storing windborne sand and providing the structure needed for land plants to take root and grow on the upper portions of the beach. Wrack also feeds many creatures that live on and in the sand, and these creatures, in turn, provide a food source for other animals such as birds. Wrack decomposes over time, releasing essential nutrients into the beach, acting as rich fertilizer for surrounding ecosystems.”

However, there may be negative health impacts on those exposed to the seaweed.

“For example, Sargassum may harbor organisms, like jellyfish, that can cause skin irritation. Exposure to hydrogen sulfide and ammonia, produced during the decay of Sargassum, may also cause mild to serious health effects, including respiratory, cardiovascular, and neurological impacts.

Additionally, Sargassum accumulates and leaches pollutants, including pesticides and heavy metals like arsenic, which could harm human health and the environment,” according to the U.S. Environmental Protection Agency.