Sargassum, the brown tide that threatens the Caribbean coast: is it here to stay?

Sargassum, the brown tide that is invading the Caribbean coast and destroying its ecosystem, is a phenomenon that was already sighted during the first European expeditions that crossed the Atlantic to reach the American continent.

More than six centuries ago, fearful that their ships would get stuck in seagrass, some explorers documented these floating meadows in the middle of the sea.

But in the last decade, this phenomenon is reaching the coastal regions, becoming a threat to the tourism sector.

It all started in the summer of 2011, when mass proliferations began to accumulate on the beaches of many destinations with crystal clear waters and white sand.

Mexico was one of the first countries to report it, but this environmental problem, lethal to many species and with harmful effects on human health, affects almost the entire Caribbean region.

This year, the amount of sargassum has already reached historic figures in the Atlantic: in June, more than 24 million tons of this brown tide were recorded on the Caribbean coast, from Puerto Rico to Barbados, according to a report from the oceanography laboratory of the University of South Florida.

What is sargassum?

Sargassum refers to the uncontrolled growth of the species

and

, brownish-colored macroalgae that live in suspension in the seas and move dragged along the Atlantic Sea by ocean currents.

Most of the macroalgae live attached to the bottom of the sea, with their roots rooted in the depths.

"But these two species are pelagic thanks to the fact that they have gas vesicles, an adaptation mechanism to improve photosynthesis and that allow them to spend their lives floating," says Rosa Rodríguez, a marine biologist at the University's Institute of Marine Sciences and Limnology. National Autonomous of Mexico (UNAM).

While the uncontrolled accumulation of these algae is toxic in coastal regions, causing the massive death of many marine species, in the high seas they play a very important role in the ecological balance.

The Sargasso Sea, in the North Atlantic Ocean, is a unique ecosystem that provides food and shelter for hundreds of species, some of them unique to this floating habitat.

In addition to serving as a platform for the protection and sustenance of marine fauna, the algae platform constitutes the migration passage for animals such as eels, turtles and whales.

Why have they become a problem?

When reaching the coasts in an uncontrolled way, the Sargassum mantles interfere with the luminosity of the ecosystems, preventing light from filtering to the seabed, which is essential for the biology of corals and for other types of algae to carry out their photosynthesis process. , affecting the biodiversity of the system they support.

A woman walks on a bridge surrounded by sargassum in Puerto Morelos, near Cancun.

EDGARD GARRIDO (REUTERS)

One quality of sargassum is its ease of growth, being able to double its biomass in less than 20 days if the conditions are favourable.

When the macroalgae decompose on the shore, they consume large amounts of oxygen, causing anoxia and emitting toxic gases such as hydrogen sulfide and methane, very dangerous for human health and responsible for the massive death of many species.

The excess of nitrogen and phosphorus from the putrefaction process itself serves as fertilizer for them to grow more, generating leachates, sulfidic acid and arsenic, substances responsible for the pestilential and already common rotten smell of some tourist destinations.

"Another problem is the poor disposal of sargassum, which ends up acting as a contaminant, as well as cadmium, lead and other heavy metals, as well as dangerous bacteria," says the UNAM specialist.

Why is it produced and where does it originate?

As they point

the strongest hypotheses, climate change would be behind the spread and uncontrolled growth of

.

For years, various scientific studies have warned of how changes in ocean currents due to the melting of the poles and glaciers, and the excess fertilization of nutrients in the oceans are favoring this phenomenon to become increasingly common.

The discharge and discharges from industries and agriculture at the mouths of the great rivers of South America, such as the Amazon and Orinoco, whose sediments and organic matter are pushed north by currents, cause macroalgae to reproduce at a record speed, proliferating explosively to create the Great Equatorial Atlantic Sargassum Belt (GASB), a new reservoir of macroalgae much larger than the original and that is devastating the Caribbean coasts.

"It is a clear example of how climate change affects us directly and indirectly," clarifies the biologist.

Which regions are being affected?

Far from being an isolated phenomenon, it impacts a large part of the Caribbean.

The beaches of Belize, Honduras, Jamaica, Cuba, Mexico, the Dominican Republic, Barbados or islands such as San Andrés, Guadeloupe or Martinique, among others, are affected by algae blankets every year.

"But large arrivals of sargassum have also reached the north coast of Brazil, and even Florida," Rodríguez points out.

This brown tide is not only impacting the Caribbean.

As the biologist explains, "it arrived in the Gulf of Mexico long before, but not in such high volumes."

A blanket of sargassum collected on the beach in Yabucoa, Puerto Rico, on August 12. Jonathan Alpeyrie (Bloomberg)

"The first report of the arrival of sargassum came from local fishermen and a newspaper in 2011," says Chuanmin Hu, an oceanographer with the University of South Florida team responsible for monitoring the growth of these marine blooms, which began tracking them in the Gulf of Mexico in 2006.

Is sargassum here to stay?

Hu is the author of an investigation that in 2019 already warned of how a change in the current regime was increasing the possibility that recurrent blooms in the tropical Atlantic and the Caribbean Sea would become the new norm.

“The data seems to indicate that the amount of sargassum reaching the coasts is increasing more and more,” he points out.

According to Rodríguez, although there is a lack of information on the biomass that is reaching the different regions of the Caribbean, and that it fluctuates every year, "everything seems to indicate not only that the problem will remain, but that it will get worse and worse." ”.

Can sargassum be mitigated?

Since the problem was pointed out by environmentalists and hoteliers, governments have sought ways to clean their affected beaches to recover tourism.

But, as Rodríguez explains, the resources invested so far have not been efficient.

“On the one hand, only a small stretch of the coast is being cared for, and ecosystems that are also affected by sargassum, such as the mangroves and the jungle, are not being protected,” he points out.

In addition, the strategy of directly removing accumulations of macroalgae from the coasts has a very negative impact.

“A little sargassum helps prevent beach erosion, but when there is a lot of it, its presence reverses the effect.

And with the heavy machinery that is used to extract the macroalgae, they take a lot of sand”, explains the UNAM expert.

Another problem derived from the removal of sargassum is the poor disposal that is made of it.

"The sargassum brings a lot of arsenic, but also cadmium, lead and other heavy metals, as well as dangerous bacteria that contaminate the environment," warns Rodríguez.

What to do with sargassum?

To the extent that it is about mitigating part of the environmental catastrophe that the region is experiencing, the arrival of sargassum in the Caribbean can be an opportunity for various industries, and in recent years different initiatives have promoted the use of this macroalgae as raw material .

The different properties of sargassum can be used for sectors ranging from construction, pharmaceuticals or the energy industry.

Research centers and universities, for example, are using its composition of lignin, cellulose and hemicellulose as a source of biofuel.

And sodium alginate, a polysaccharide that these sea vegetables also contain and that acts as a thickener, is even used in the textile industry and haute cuisine.

Promoting the principles of the circular economy, which uses everything and also creates added value, some companies are taking advantage of the impurities left over from the alginate extraction process, such as fucoidans.

These biopolymers, whose antitumor and immunomodulatory properties are under investigation, could be used as therapies even against cancer, according to some studies.