New understanding of sargassum origin may help predict where it'll go

• Scientists at the University of Miami have found that sargassum may have a different origin than previously anticipated.
• Their findings suggest that North Atlantic Sargassum blooms actually come from West Africa, not the Sargasso Sea.
• South Florida frequently sees sargassum washing ashore on its beaches, but the brown seaweed generally isn't harmful to humans.

Scientists at the University of Miami have found that some sargassum, the brown seaweed that regularly washes ashore on Florida's beaches, may have a different origin than previously anticipated.

Their findings, published in the journal PNAS Nexus in March, suggest that the first significant recorded North Atlantic sargassum bloom, which occurred in 2011, actually came from West Africa, not the Sargasso Sea.

“Sargassum blooms have had enormous ecological and economic impacts across the Caribbean, Gulf of Mexico, South Florida and West Africa,” said Francisco Beron-Vera, lead author and research professor in the Department of Atmospheric Sciences at UM's Rosenstiel School. “Our results provide strong evidence that these blooms begin in the eastern tropical Atlantic, not in the Sargasso Sea as previously thought.” 

According to the University of Miami, "vast accumulations of floating Sargassum known as the Great Atlantic Sargassum Belt" have popped up across the tropical Atlantic since 2011, "affecting coastal ecosystems, fisheries and tourism." In Florida alone, the blooms could cost the state $3.63 billion, given impacts to hotels, restaurants, fisheries and charters. Their origin has remained a "subject of debate."

A stronger understanding of where sargassum blooms come from could help researchers better predict "future events," said co-author María Josefina Olascoaga.

Sargassum impacts across South Florida

The Southeast coast and the Florida Keys are usually most heavily impacted by mounds of sargassum washing ashore — throughout April, the seaweed was already cropping up in places like Cocoa Beach and Miami Beach.

Last year, the amount of sargassum in the Atlantic set a new all-time record for the month of April. For 2026, it's set to be another “major sargassum year,” meaning the amount exceeds 75% of the historical values, according to a March bulletin by the University of South Florida. The report adds that it's likely to be a “record year” by the summer.

Although it can be an irritant to beachgoers, sargassum plays an important role in marine ecosystems, according to the Florida Fish and Wildlife Conservation Commission.

What is sargassum?

Sargassum includes pelagic species of brown seaweed that have their origin offshore in the Atlantic Ocean and float on its surface, according to the FWC. It’s a vital marine resource, and provides habitats for animals like shrimp, crabs, sea turtles and fish. Species like mahi mahi, jacks and amberjacks also use it as a primary nursery area.

Can you touch sargassum at the beach in Florida?

While sargassum is generally safe to touch, it can play host to small organisms that can sting you, so it’s best to try and avoid swimming near it.

Where is the Sargasso Sea?

The Sargasso Sea was named after sargassum, according to the Sargasso Sea Commission. The commission is creating a conservation system for the area under two different projects.

The commission's website says the Sargasso Sea is a 2 million square mile open ocean ecosystem, bounded by the circulating currents of the North Atlantic Gyre, one of five sea gyres which are geographic rotating currents.

Sarah Perkel is a South Florida Connect Reporter for the USA TODAY Network's Florida Connect team. You can get all of Florida’s best content directly in your inbox each weekday day by signing up for the free newsletter, Florida TODAY.