Sargassum: The macroalgae that's suffocating the Mesoamerican Reef

Sargassum near Tulum, Mexico
El Universal
Cancún, Mexico
Sargassum: The macroalgae that's suffocating the Mesoamerican Reef

“I have never imagined that I would see the reef I described die, when I was young and studying biology,” said science communicator Patricia Santos, speaking about the rapid degradation of coral reefs in the Mexican Caribbean due to in part to global warming and to the arrival of sargassum, a pelagic macroalgae that alters water conditions, and coral tissue loss disease, or white syndrome, as it’s known in Spanish.

During a talk at the end of November inside a private hospital in Cancun, Santos addressed a group of doctors gathered for the first time to understand how rising temperatures have begun to negatively affect the health not only of marine ecosystems but also of humans.

She explained how hyper-consumption and the pollution of air, water and land sharpen climate change’s impacts and plunge the planet into an environmental crisis that compromises the existence of all living beings, especially people.

The situation, she confessed, has driven her into therapy, fearing the certainty that humanity is losing ground in the face of environmental crises.

"If we lose the battle for environmental conservation, no other battle will make sense,” said Santos.

The biologist and feminist, who serves as head of the department of the natural protected area “Mangroves of Nichupté” in Cancun, agrees with other scientists on the possible local extinction of coral species; first in the Mexican Caribbean then later in the Mesoamerican Reef System (or MAR), a giant barrier reef that extends from Mexico through Belize and Guatemala to Honduras.

She even goes further when she talks about the possible loss of the entire coral reef ecosystem – or its probable mutation.

“There are those who affirm that the first ecosystem victim of global warming will be the reefs,” she said. “The phenomena are happening so fast, that the [individual] species will not be able to adapt.

“If the reef ecosystem does not die out, it will become another ecosystem, a 'mutant' reef, we cannot know,” she warned in an interview with El Universal.

‘The dead ones are protecting us’

On the morning of November 1st, after diving among the reef to show its status, María del Carmen García Rivas, director of the Puerto Morelos Reef National Park, admits that the loss of the reef is a possibility.

The mortality of some coral species has accelerated with the white syndrome, leaving rock beds without environmental services, she explained. 

White syndrome kills corals’ living tissue, undressing its calcium carbonate skeleton and leaving it defenseless to the recolonization of other organisms. Without living tissue, the coral becomes a stone that will be eroded naturally over time until it becomes flat or disappears.

“You always have been prepared for the worst scenario. If there is no reef, the erosion would be impressive, it would not give us even 10 years to move from the coast to another site,” said García Rivas.

“If another emerging phenomenon arrives tomorrow and destroys all the calcium carbonate skeletons - because now we have a barrier of skeletons - the reef would be flat (...) it is a tragedy, an affectation never seen,” she added.

Maria Garcia Rivas
María del Carmen García Rivas, director of the Puerto Morelos Reef National Parks, says without the MAR ecosystem, erosion would be extreme / Credit: Adriana Varillas

In this situation, García Rivas sees the prelude to a greater disaster: The collapse of other ecosystems, whose social repercussions will be stronger than environmental ones.

“We will have social chaos here, to fight for water, for food. Like those science fiction movies, you said ‘I wish it never happened.’ But it seems to me that it is no longer science fiction.

“In the case of Puerto Morelos, our water goes first to the hotel zone, then to the town (…) and we continue allowing developments, thinking that having a job is the best thing in life,” she said. “The problem is that our engine is money and is an engine that is killing us.”

Expected and emerging phenomena

With postgraduate studies in coastal ecology, marine invertebrates and restoration of mangrove ecosystems, Patricia Santos explains that the Mesoamerican Reef is the target of unimaginable phenomena that are known as “emergent,” not because of their degree of urgency or “emergency,” but because they “emerge” from the change in ecosystem conditions to give rise to other situations, equally unthinkable.

“Speaking of global phenomena, the predicted phenomena are those that theoretical models already announced to us as a direct effect of the atmosphere: Temperature increase, the melting of the poles, the loss of ice mass and probably cyclones, hurricanes, droughts, floods. Those are phenomena that were anticipated to occur,” she explained.

Rosa Rodríguez, who specialized in coral reef ecology at the Institute of Marine Sciences and Limnology (ICMyL) at the National Autonomous University of Mexico (UNAM), agrees.

“Both the massive sargassum relapses and the white syndrome are emerging phenomena; nobody knew what was going to happen, nobody expected them to happen in the magnitude they are happening. Sargasso had already arrived before and diseases that had affected corals in the Mexican Caribbean, but not in the magnitude that we are seeing in recent years,” Rodríguez said.

“It is something we were not prepared for and that it is taking us a long time to try to understand and resolve and this is causing severe environmental damage.”

Rosa Rodriguez
 Rosa Rodríguez, a specialist in coral reef ecology / Credit: Adriana Varillas

Water quality vs reef health

The scientific community that studies white syndrome agrees that its rapid spread in the Mexican Caribbean is linked to poor water quality. The disease causes the detachment of living coral tissue.

Human actions, “which we elegantly call climate change,” have changed the environmental conditions of water ideal for coral and caused imbalances that, little by little, are aggravated by the actions of nature itself, said García Rivas.

As an example, she points to Cancun, which took off as a beach resort 50 years ago in April.  According to García Rivas, its tourist infrastructure was conceived in a planned way, almost perfectly, under a massive model that got out of control.

The resort destination was developed on coastal dunes, which sharpened the natural erosion of the beaches; mangroves, which filter contaminants and keep them from reaching the sea, were cut down and filled in; seagrasses were damaged and the lagoon and seawater became cloudy. Sewage was treated improperly or even emptied without treatment.

“We continue to handle wastewater and waste poorly,” García Rivas acknowledges. “We put nitrogen into the ecosystem, phosphates that are not ideal for corals, organisms that grow and develop in sterile, clean, clear, nutrient-free waters.”

Polluted water is favorable for the flowering of algae and macroalgae, like sargassum, which in large quantities “provides an additional stress factor to corals,” says Santos.

A breeding ground for bacteria and viruses

The sargassum that reaches the Mexican Caribbean is a pelagic macroalgae that reproduces in a clonal manner, that is, asexually, floating in the sea. It doubles its amount of living matter (biomass) in 18 days.

Its origin dates back to the so-called Sargasso Sea, an ecosystem described by Christopher Columbus in 1492, located in the Bermuda Triangle, says Brigitta Van Tussenbroek, a researcher at ICMyL.

Brigitta Van Tussenbroek
Brigitta Van Tussenbroek, a researcher at ICMyL / Credit: Adriana Varillas

“What happened is that a new Sargasso Sea or a new flourishment of these algae was generated in a region where it was not abundant, which is the South Atlantic, between Africa and Brazil, and in 2010 unique conditions were generated that detonated the flowering of the two species of sargassum,” she explains.

In agreement with other scientists, Van Tussenbroek and Rodríguez Martínez, indicate that sea currents, probably affected by global warming, moved huge masses of these macroalgae to the Caribbean, creating a "huge" ecological imbalance.

Van Tussenbroek specialized in the study of sargassum as a result of her atypical arrival in the Mexican Caribbean in 2015 and its impacts on seagrasses, a subject of her expertise.

Rodríguez Martínez, specializing in coral reef ecology, also focused on monitoring the evolution of macroalgae, which virtually disappeared naturally in 2016 and 2017. In 2018 sargassum returned in such large quantities that it became a menace to businesses and local governments. Last year was no different, said Rodríguez Martínez.

The effects of sargassum on corals

The volumes of these brown macroalgae are such that when they reach shallow waters they form floating carpets that block the passage of sunlight necessary for the photosynthesis of a type of microalgae called zooxanthella, which lives in close relationship with the coral and provides them with energy, explained Rodríguez Martínez.

Once on the shore of the coast, the sargassum accumulates and rots, releasing components that in addition to dyeing the water ocher, represent a potent supply of nutrients and organic matter that affects the coral, weakening its defenses against pathogens and bacteria and reducing its reproductive strength, said Van Tussenbroek.

“The decomposition of sargassum and an additional factor, which we did not take into account, is sulfuric acid, which generates an impressive rise of temperature, up to 3 or 4 degrees,” underlines García Rivas.

“On the other hand, all the transparency of the water is changing and this brown tide is going to the reef, in addition to the bacteria it generates. Perhaps here came the pathogen of the white syndrome.”

Patricia Santos
Science communicator Patricia Santos is a biologist with a weekly program on Mexican radio where she explains science to non-specialized audiences / Credit: Adriana Varillas

At present, the scientific community does not know if the pathogen causing the disease is a bacterium, fungus or virus. They do not have a specific treatment. They have tried with a mix of antibiotics and natural ingredients, but none have worked.

For Van Tussenbroek, the sargassum did not necessarily contribute the pathogen, but it did deteriorate the quality of the water.

“This causes stress to the coral, and it is like people, if we are under a lot of stress, a disease arrives and affects us much more. The pathogen did not necessarily arrive with the sargassum, but since the coral was already stressed by global warming, the deterioration of water quality due to a lack of plants [to treat or clean polluted water] and, now, by sargassum, it makes it more susceptible,” she said.

According to some hypotheses, the contribution of pollutants or toxins from these brown waters is eight to 14 times greater than that generated by the urbanization and tourist development of the town of Puerto Morelos. Oceanologist Melina Soto says that only 38 percent of the homes in the town are connected to proper drainage; the rest use septic tanks and do not maintain them, allowing polluted water to enter the ocean and damage coral habitats.

Impacts to the coral reef

Soto is the coordinator in Mexico of Healthy Reefs for Healthy People, an initiative that brings together other organizations to monitor the health of the Mesoamerican Reef and generate management recommendations for the conservation of this ecosystem – one composed of atolls and islands and bordering more than 1,500 kilometers of coastline.

“Until last year I would have told you that the hardest hit for the reef was macroalgae, which for 10 years has doubled or more its coverage,” said Soto.

Today white syndrome is the number one cause of mortality in the reefs of Quintana Roo. On a regional scale, water quality with a high nutrient load and coral bleaching due to the increase in water temperatures continue to be the greatest threats, cites Soto as part of the diagnosis.    

Losing the reef, she explains, implies compromising the food security of millions of people settled in the Mesoamerican and Caribbean region, the habitat of numerous species of commercial fish, the sand of the beaches, the scenic attractions that seduce tourists and protection against extreme weather events.

For Van Tussenbroek, this last point is a big concern.

“Already a lot of coral died [due to] the bleaching, the syndrome and are losing the three-dimensional structure that can dissipate the energy of a hurricane. If at this moment a hurricane hits us like Wilma did 14 years ago, my forecast is that our coast will be less protected and we will suffer more than in 2005 with that hurricane,” she said.

Spanish-language version of this story first appeared in El Universal on 24 Dec. 2019. It was produced with the support of the Earth Journalism Network's Mesoamerican Reef Reporting Project.

* Translation by Alejandra Serrano Pavón

Banner image: Sargassum lays in clumps along the beach in Quintana Roo, Mexico / Credit: Stephen Rees via Flickr 

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