Sargassum seaweed blooms plaguing Atlantic beaches traced back to West Africa
Large influxes of floating Sargassum affect coastal ecosystems, fisheries and tourism.
FILE: Smelly sargassum seaweed invades Florida beaches
Record-breaking blooms of smelly sargassum seaweed are invading Florida beaches. FOX Weather Correspondent Brandy Campbell was in Dania Beach on July 23 and explains that even though the brown microalgae can be beneficial for marine life, it can become a mess after decomposing on the beach.
A new study traced the origins of Sargassum seaweed, an unwelcome and smelly sight at beaches in the tropical Atlantic, back to West Africa.
For years, Sargassum seaweed has popped up on beaches in Florida and other coastal places in the Atlantic during spring and summer, when people are flocking to beaches.
Large influxes of floating Sargassum affect coastal ecosystems, fisheries and tourism.
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People sit on the sand in south beach, Miami during the seasonal surge of Sargassum seaweed, on July 21, 2025.
(DANIEL SLIM/AFP via Getty Images / Getty Images)
Scientists from the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science and collaborators used two different methods to trace the origin of the first major sargassum bloom for their study published in PNAS Nexus.
Sargassum has been washing up on beaches in the tropical Atlantic since 2011, and the origin has long been up for debate, according to the University of Miami Rosenstiel School.
The new study identifies West Africa, rather than the Sargasso Sea, as the primary source of the seaweed.
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"Sargassum blooms have had enormous ecological and economic impacts across the Caribbean, Gulf of Mexico, South Florida and West Africa," said lead author Francisco Beron-Vera, a research professor in the Department of Atmospheric Sciences at the Rosenstiel School. "Our results provide strong evidence that these blooms begin in the eastern tropical Atlantic, not in the Sargasso Sea as previously thought."
Swaths of sargassum, or seaweed, washed up in Key Biscayne on Thursday, April 24 and was raked into piles to be taken to the landfill.
(Ashley Miznazi/The Miami Herald/Tribune News Service via Getty Images / Getty Images)
According to the Rosenstiel School, researchers used two independent analytical approaches: Bayesian inversion, which estimates the most likely source based on where and when the bloom was observed, and transition path theory, which identifies the most efficient transport pathways feeding the bloom.
Both methods pointed to the same origin: the Gulf of Guinea near coastal West Africa.
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The study also linked the bloom to unusual environmental conditions in 2009 and 2010.
Sargassum algae piles up along the shore at a beach in Puerto Rico on May 19, 2025
(Photo by Ricardo ARDUENGO / AFP / Getty Images)
The Rosenstiel School said an event marked by cooler sea surface temperatures and enhanced nutrient-rich upwelling off West Africa likely created favorable conditions for rapid Sargassum growth. Additional nutrient inputs from Saharan dust and increased river runoff may have further fueled the bloom.
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"These conditions appear to have provided the right combination of nutrients and ocean dynamics to trigger large-scale growth," said co-author María Josefina Olascoaga, a professor in the Department of Ocean Sciences.
PUERTO JUAREZ, MEXICO - DECEMBER 16, 2023: A family enjoys a dip in the sea at a beach covered with sargassum seaweed on December 16, 2023, in Puerto Juarez, Cancun, Quintana Roo, Mexico.
(Photo by Artur Widak/NurPhoto via Getty Images / Getty Images)
Biological evidence also supported their findings. The main type of Sargassum during the first years of the bloom in the tropical Atlantic were different from the types found in the Sargasso Sea, the study showed.
"Understanding the origin of these blooms gives us a much stronger foundation for predicting future events," Olascoaga said.
Researchers suggest that low background concentrations of Sargassum already present in the tropical Atlantic expanded rapidly once environmental conditions became favorable.