From Belize to Barbados, tourist beaches have been swamped by huge tides of foul-smelling sargassum – and climate change could make the problem worse

“It was like something out of a science fiction movie,” says Barbara Hall from the office of the beachside hotel she runs in Placencia, southern Belize.

“I woke up at 6am, looked out my window and realised we had a big problem. It was absolutely overwhelming.”

The sight that greeted her that morning was a gargantuan tide of sargassum – a type of ocean seaweed that had swept in overnight. At sea, sargassum is an essential habitat for some marine life, but when it reaches land it rots, sucking up oxygen from the water and emitting hydrogen sulphide gas, which smells like rotten eggs.

Facebook Twitter Pinterest The influx of sargassum seaweed has been accumulating along the coast of Ambergris Caye. Photograph: Courtesy of The San Pedro Sun Newspaper

It has washed up in the Caribbean in unusually large amounts since 2011, but this year the largest volumes ever have appeared on shores from Barbados to Mexico, with piles several feet deep stretching for miles, and dozens of metres out to sea.

It has had a significant effect on the tourism on which much of the region depends – the sight and smell left beaches highly unattractive, and swimming was impossible. On land, the gas rapidly destroyed nearby electric units, such as TVs; eroded metals and even affected human health, with people living near inundated areas complaining of headaches, nausea and skin irritation.

Marine life was also affected; across the region, there have been reports of fish, turtles, dolphins and other creatures succumbing to the piles of rotting algae.

While oceanographers are uncertain of its causes, they think global warming could be a factor, and coastal communities could be due even worse sargassum inundations in the future.

“This is a major issue for many island countries,” says James Franks, senior research scientist at the Gulf Coast Research Laboratory at the University of Southern Mississippi. “We don’t fully understand it … there are many unknowns.”

Facebook Twitter Pinterest Sargassum seaweed on the Salines beach in Le Gosier, Guadeloupe. Photograph: Helene Valenzuela/AFP/Getty Images

It is believed the sargassum has benefited from increased nutrients in the sea – perhaps from mineral-rich dust blown from Africa, Franks says. Others believe fertiliser runoff from industrial farming in the Americas may be to blame. Warmer waters would also encourage plant growth.

“I imagine global warming is part of the problem,” says Amy Siuda, a sargassum specialist at Eckerd College, Florida. “We’re experiencing changes in currents that certainly can be related to warming of the atmosphere.”

Changes in wind patterns – potentially caused by a warming climate – mean sargassum might have been moved from areas where it has usually stayed, with winds and currents bringing it further south than normal, Siuda says.

She adds: “Ocean currents are the results of winds, changes in winds are the results of solar heating and changes in atmosphere and circulation. Ultimately, we can change circulation patterns by warming our atmosphere.”

Regardless of the causes, sargassum is being taken so seriously that governments across the Caribbean have initiated emergency programmes to deal with the issue.

Facebook Twitter Pinterest Workers clear Sargassum algae at Gaviota Azul beach in Cancun, Mexico. Photograph: Victor Ruiz Garcia/Reuters

Belize, a tiny nation in Central America, is highly dependent on tourism, and sargassum is the “biggest concern” of all to the trade, says Hall.

Hall says the authorities are “doing a good job” and are preparing the funding needed for expensive and complicated clear-up operations. Nonetheless, some hotels have reported cancellations during the slow season. The impact during high season could be devastating, say numerous locals employed in tourism.

Hall stresses that hotels are taking firm steps to deal with the issue – such as preparing booms to keep the tides of sargassum out at sea – and they remain optimistic for the region’s future. But she admits some sargassum control methods employed in the nearby Yucatan peninsula of Mexico – which is much better-resourced – have not worked.

In the northern Belizean island of Ambergris Caye, there was a mass fish die-out. The sargassum is “wiping out a generation” of the area’s young sea creatures, says Kirah Castillo, technical manager of the Hol Chan marine reserve just off the island.

Months-old juvenile creatures such as lobster and conch migrate to nursery areas of mangrove and seagrass and are believed to have been suffocated by sargassum. “Whatever juveniles came in will have died,” Castillo says. The effects are likely to be felt in two to three years’ time, when the creatures would be due to enter the fishery, she says.

These creatures are hard to see and the phenomenon has not been measured, Castillo says, but “we know from the biology of these animals that it is happening and will have an effect on the ecosystem. That’s a major concern for us.”

Facebook Twitter Pinterest A woman walks on a makeshift bridge near sargassum algae in Puerto Morelos, near Cancun, Mexico. Photograph: Edgard Garrido/Reuters

The complex suspected causes of the sargassum problem mean it could worsen, with little prospect of a preventive solution.

“Everyone now recognises this is a critical issue and may be long-term,” says Franks. Siuda agrees: “If the inundations increase in frequency, they could potentially last all year long without a break, maybe in larger amounts.”

It represents a new challenge coastal communities will have to adapt to.

“You couldn’t stop the waves. You could just see it coming and coming,” says Hall in her hotel office. “It’s a difficult thing, to feel powerless.”