Huge masses of foul-smelling seaweed in the Caribbean could give sun-seekers headaches

Every winter, millions of Canadians travel to the Caribbean in search of sunshine, pristine beaches and crystal clear waters.

This year, however, tourists may have noticed something not so pleasant waiting for them on the beach: brown, smelly sargassum.

Over the past decade, stinking algae has become more common on beaches in the Caribbean and the South Atlantic Ocean. So what’s going on? To understand, you must first understand Sargassum.

What is sargassum?

Sargassum is a type of brown algae (and a form of seaweed) found in the Atlantic Ocean. It is made up of pieces of leaves, as well as round berry-like pieces filled with oxygen that help it float to the surface. It has neither roots nor seeds.

Unlike some other types of algae, it lives its entire life on the surface of the ocean in small patches. Sargassum is usually found in a region called Sargasso Seawhere it tends to circulate in a vortex called a gyre, through a five million square kilometer belt that stretches from the Chesapeake Bay in the mid-Atlantic to the Caribbean.

However, Sargassum can clump together, creating rafts or patches. It has a seasonal cycle, beginning in the spring, peaking in the summer, and finally disappearing in the fall.

Sargassum is a leafy brown algae that lives and reproduces on the surface of the Atlantic Ocean. (Alexander Meneghini/Reuters)

Sometimes large collections can wash up on beaches, which can be an annoyance for beachgoers. But they are vital to certain marine species, providing food and breeding grounds for animals such as fish, sea turtles and more.

“[Sargassum] formed these huge floating masses on the high seas, which are wonderful, actually…because they take in carbon, they suck in nutrients, they support a lot of life and a lot of animals depend on them,” said Brigitta Ine van Tussenbroek , scientist at the Institute of Marine Sciences and Limnology of the National Autonomous University of Mexico.

“Even the American eel, the northern European eel, they wouldn’t exist without the Sargasso Sea, for example. So it’s a wonderful system.”

Is it increasing?

While most Sargassum usually stays in this gyre, it can travel along a kind of conveyor belt in the Atlantic and the Caribbean. Scientists have found a noticeable increase in sargassum washed up on Caribbean beaches since 2011.

“Sometimes some of these vortices… loosened up, and some of the sargassum escaped, then went to Cuba, to Hispaniola, and some ended up in Mexico, goes through the Gulf of Mexico. And then they’re returned to the Sargasso Sea”, van says Tussenbroek.

“Since 2010-2011, all of a sudden, Sargassum started accumulating in a new area just north of the equator in the tropical Atlantic.”

A man stands on brown mounds of sargassum on a beach.
Park ranger Roberto Varela walks on sargassum seaweed piled up by the sea in the Guanahacabibes peninsula, Cuba, June 27, 2022. (Alexander Meneghini/Reuters)

Why does this happen? Scientists aren’t sure.

A number of factors could be at play, including climate change and human activity, van Tussenbroek said.

Chuanmin Hu, a professor at the University of South Florida who studies these flowers with their Sargassum monitoring system (SaWS), said a lot of the nutrients come from the dust from the Saharan desert that crosses the Atlantic Ocean.

But there’s also ocean upwelling, he said, where water from the depths of the ocean is brought to the surface, and with it, more nutrients, further promoting these blooms. And, scientists believe that with a climate change, there could be more ocean upwelling. Additionally, nutrients flow into the Atlantic from the Congo River in Africa and the Amazon River in South America.

“Now the question is, who is dominant?” Hu said. “We just don’t know. It’s hard to quantify their contributions.”

What is the situation this year?

According to SaWS, January was the second month in a row that Sargassum doubled, which last happened in 2018. Although it fell in February, it is believed to continue to grow and recover way along the coasts of the Caribbean nations. Last year saw the highest number of Sargassum ever recorded.

But so far this year has been impressive, Hu said, adding that in December SaWS predicted that 2023 could be another banner year, although there are no guarantees.

“All we can say is that it would be another major year.”

How many are there?

In January, there were more than eight million metric tons of Sargassum in the Atlantic Ocean, Hu said. In February, that figure fell to between six and seven million metric tons. But Hu said there could be even more in March.

“Right now, they are scattered here and here with low density. Even in the belt, the density is less than 0.1 percent,” Hu said. “But if someone could put all the Sargassum in one place, how big would it be? It’s about, I think, 3,000 square kilometres, without space.”

Brownish green sargassum floats in the blue ocean.
An aerial view of sargassum seaweed in Cancun on August 13, 2015. (Edgard Garrido/Reuters)

What are the effects of large flowers?

These large blooms that scientists have seen develop since 2011 are problematic. First, hotels and cities must bear the cost of eliminating these masses, in order to protect a lucrative tourist industry.

Then there is the concern about ecosystems.

A worker in a white shirt and black pants shovels brown sargassum into a wheelbarrow.  The shore is covered with it.
Workers clean up Sargassum seaweed along Punta Piedra beach in Tulum, in the Mexican state of Quintana Roo, August 11, 2018. (Israel Leal/Reuters)

An abundance of Sargassum can threaten delicate shoreline ecosystems, as well as smother coral reefs, reducing their cover and roughness, making them more sensitive to waves and less protected from hurricanes. It can also prevent fledgling sea turtles from reaching the ocean.

The good news is that there could be uses for Sargassum masses, including as biofuel or even as a building material.

Should I be worried?

If you’re heading to the beach and come across these lumps, there’s no immediate concern, although the decaying smell can be unpleasant. And it could ruin any snorkeling or offshore swimming you might be craving.

“What I want to say now, you know to tourists, is don’t panic,” Hu said. “It is a natural plant, it is not toxic. If you have too much, if [it decomposes]it can be harmful, but it’s not toxic most of the time,” Hu said. “

“And also most of the time, even if they accumulate on the beaches, the locals usually remove them. So if you have travel plans, come to Florida, come to the Caribbean. I wouldn’t worry things.”

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