Sargassum, the brown tide that is invading the Caribbean coast and destroying its ecosystem, is a phenomenon that was already sighted during the first expeditions of Europeans who crossed the Atlantic to reach the American continent. More than six centuries ago, fearful that their ships would get stuck in the seaweed, some explorers documented these floating meadows in the middle of the sea. But in the last decade, this phenomenon is reaching coastal regions, becoming a threat to the tourism sector.
It all started in the summer of 2011, when massive proliferations began to accumulate on the beaches of many destinations of 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 coasts, from Puerto Rico to Barbados, according to a report by the oceanography laboratory of the University of South Florida.
What is sargassum?
Sargassum is the name given to the uncontrolled growth of Sargassum fluitans and S. natans, brownish-colored macroalgae that live in suspension in the sea and are carried along the Atlantic Ocean by ocean currents. Most macroalgae live attached to the sea floor, with their roots rooted to the depths. “But these two species are pelagic because they have gas vesicles, an adaptive mechanism to enhance photosynthesis and allow them to spend their lives floating,” notes Rosa Rodriguez, a marine biologist at the Institute of Marine Sciences and Limnology of the National Autonomous University of Mexico (UNAM).
While the uncontrolled accumulation of these algae is toxic in coastal regions, causing the massive death of many marine species, on 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 serves as 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 wildlife, the kelp shelf is a migration passage for animals such as eels, turtles and whales.
Why has this become a problem?
When they reach the coasts in an uncontrolled manner, the Sargassum mats 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.
One quality of sargassum is its ease of growth, being able to double its biomass in less than 20 days if conditions are favorable. When macroalgae decompose on the shore, they consume large amounts of oxygen, causing anoxia and emitting toxic gases such as hydrogen sulfide and methane, which are very dangerous to human health and responsible for the massive death of many species.
The excess nitrogen and phosphorous from the putrefaction process itself serves as fertilizer for them to grow more, generating leachates, sulfuric acid and arsenic, substances responsible for the pestilent and now common rotten smell of some tourist destinations. “Another problem is the poor disposal of sargassum, which ends up acting as a pollutant, as well as cadmium, lead and other heavy metals, as well as dangerous bacteria that contaminate the environment,” says the UNAM specialist.
Why is it produced and where does it originate?
According to the strongest hypotheses, climate change would be behind the uncontrolled extension and growth of Sargassum. For years, several scientific studies have been warning of how changes in ocean currents due to the melting of the poles and glaciers, and the excessive fertilization of nutrients in the oceans are making this phenomenon increasingly common.
The discharge and dumping of industrial and agricultural waste at the mouths of the great rivers of South America, such as the Amazon and Orinoco, whose sediments and organic matter are pushed northward by currents, cause macroalgae to reproduce at record speed, proliferating explosively to create the Great Equatorial Atlantic Sargasso Belt (GASB), a new reservoir of macroalgae much larger than the original and which is sweeping the Caribbean coasts. “It is a clear example of how climate change affects us directly and indirectly,” says the biologist.
Which regions are being affected?
Far from being an isolated phenomenon, it is impacting a large part of the Caribbean. The beaches of Belize, Honduras, Jamaica, Cuba, Mexico, Dominican Republic, Barbados or islands such as St. Andrew, Guadeloupe or Martinique, among others, are affected by the algae bloom every year. “But large arrivals of sargassum have also reached the northern coast of Brazil and even Florida,” Rodriguez points out. This brown tide does not only impact the Caribbean. As the biologist explains, “it arrived in the Gulf of Mexico much earlier, but not in such high volumes”.
“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 it here to stay?
Hu is the author of research that in 2019 already warned how a shift in the current regime was increasing the likelihood that recurring blooms in the tropical Atlantic and Caribbean Sea would become the new norm. “The data seems to indicate that more and more sargassum is coming ashore,” he notes. According to Rodriguez, although much information is lacking on the biomass that is reaching the different regions of the Caribbean, and which fluctuates every year, “everything seems to indicate not only that the problem will remain, but that it is going to get worse and worse”.
Can it be mitigated?
Since the problem was pointed out by environmentalists and hoteliers, governments have been looking for ways to clean up their affected beaches in order to recover tourism. But, as Rodriguez explains, the resources invested so far have not been efficient. “On the one hand, only a small extension of the coast is being attended to, and ecosystems that are also affected by sargassum, such as mangroves and jungle, are not being protected,” he points out.
In addition, the strategy of directly removing macroalgae accumulations from the coasts has a very negative impact. “A little sargassum helps prevent beach erosion, but when there is a lot, its presence reverses the effect. And with the heavy machinery that is used to extract the macroalgae, a lot of sand is removed,” explains the UNAM expert.
What to do with sargassum?
In order to mitigate 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 various initiatives have promoted the use of this macroalgae as a raw material.
The different properties of sargassum can be exploited for sectors ranging from construction, pharmaceuticals or the energy industry. Research centers and universities, for example, are using its lignin, cellulose and hemicellulose composition as a source of biofuel. And sodium alginate, a polysaccharide that is also contained in these sea vegetables and acts as a thickener, is even used in the textile industry and in haute cuisine.
In line with 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 anti-tumor and immunomodulatory properties are currently under investigation, could even be used as cancer therapies, according to some studies.
