Coastal Atlantic sargassum impact: URI's Tracey Dalton analyzes economic impact of harmful macroalgal blooms

Sargassum, a hardy brown seaweed in the Caribbean, has been floating through seafarer’s logbooks for centuries, but what impact is it having in the region today?

In a new paper, University of Rhode Island Marine Affairs Professor Tracey Dalton and colleagues are updating the current literature about sargassum, with a look at its real economic impact.

Dalton recently published a paper on the algae’s impact with Di Jin, a URI alumnus now a senior scientist at the Woods Hole Oceanographic Institution’s Marine Policy Center.

Their paper provides the most comprehensive assessment to date of the economic damage caused by recurring sargassum inundation events across U.S. coastal regions. The research quantifies multi-million dollar, and in some areas potentially more than a billion, in annual losses affecting Puerto Rico, the U.S. Virgin Islands, and Florida’s Atlantic coast.

Funded by NOAA’s National Centers for Coastal Ocean Science Competitive Research Program, the new study addresses a critical knowledge gap, examining the seaweed’s economic impact.

“While the ecological and public health impacts of sargassum inundation events have been widely documented,” says Dalton, “their direct and indirect economic costs to governments, coastal communities, and private industries had not previously been quantified.”

“These results highlight the urgency of sustained investment in sargassum monitoring, forecasting, and cleanup infrastructure,” she says. “Without proactive management, the economic consequences for coastal communities will continue to escalate.”

Dalton credits her former Ph.D. student, Ken Hamel ’24, now working with the USDA Forest Service, for playing a pivotal role in initiating the project. Hamel studied phycology while pursuing his master’s degree so he brought an interest in seaweeds and other algae to URI. The two published related articles on sargassum events, illustrating the seaweed as a significant regional problem with a number of negative impacts. In fact, such events are considered a new type of natural disaster.

“We spent a lot of Ken’s early days in the marine affairs program talking about the intersection of seaweed and people,” Dalton says. “Communities across the Caribbean were experiencing health, economic, and social impacts from these events, but studies on these impacts were limited.”

Both Dalton and her URI colleague Carlos Garcia-Quijano, a professor of anthropology and marine affairs, had done research in Caribbean communities over the years, so the three of them started building a collaborative interdisciplinary study of sargassum impacts on local communities in the Caribbean and brought in Jin at Woods Hole, who has expertise conducting economic impact analyses of harmful algal blooms.

Prior to 2011, there were small sporadic amounts of sargassum in the Caribbean region, Dalton says, but satellite studies showed the first major sargassum event in the region in 2011. Multiple factors influence the timing and extent of sargassum blooms in the Caribbean, and scientists are still trying to understand how all of these factors contribute to these events.

Their paper in the new issue of Harmful Algae documents these rising events in the region, and social and economic disruptions in the area. Using field observations from the Sargassum Watch database, they validate Sargassum forecasts in the region, showing that the sargassum season has started earlier and lasted longer in recent years. In 2025, nearly 38 million metric tons of sargassum were observed in the Caribbean, the Atlantic and the Gulf of Mexico, breaking historical records. Such events can cause considerable physical, ecological and socioeconomic impacts and have negative impacts on human activities such as tourism, hospitality, fishing, lodging, boating, real estate, and the cruise industry.

The team’s results will provide important input for deciding the direction of future sargassum response and cleanup.

Risk levels were shown to be highest in Puerto Rico and the Virgin Islands, along Florida’s eastern coast and panhandle. The risk level was generally low along Florida’s west coast, since the dominant winds blow east to west, away from the shoreline, pushing the sargassum away from the coast.

In eastern Florida, Puerto Rico and the Virgin Islands, the sargassum risk level peaks in May or June.

In recent years, sargassum inundation has been getting worse each summer, with the season starting earlier and lasting longer.

Due to the frequency of events, annual expected impacts are higher along Florida’s east coast, with a $2.7 billion direct impact in the region; for Puerto Rico and the Virgin Islands, the annual expected direct impact is more than $100 million.

Future studies could examine connections between economic activity and sargassum blooms and other economic impacts including human health concerns. Another dimension is beneficial uses for sargassum, including for fertilizer, animal feed and even biomass for power generation.