A new disease is killing the corals of the Mexican Caribbean
A diver observes a coral reef in the Mexican Caribbean.
A diver observes a coral reef in the Mexican Caribbean.Lorenzo Alvarez-Filip

A new disease has become the last executioner of the corals of the Mexican Caribbean. The outbreak, first identified in Florida in 2018, reached Mexico’s shores at least four years ago. Since then it has continuously devastated the reefs of the Mayan Riviera. A study, published this Thursday in the scientific journal Nature, points out that the disease has affected at least 21 coral species, some of them designated as structural because they help maintain the functionality of these ecosystems. At least 17% of the corals analyzed in more than 29,000 colonies died from this condition. The authors say it is likely to become the “deadliest ever recorded in the Caribbean.”

White syndrome or hard coral tissue loss disease (SCTLD). Those are the names that have been given in Spanish to this new condition that besieges the second largest barrier reef in the world, the Mesoamerican Reef System, and about which there is still little information. At first it was thought that it was a bacterial infection, says Lorenzo Alvarez-Filip, author of the study and researcher at the Institute of Marine Sciences and Limnology of the National Autonomous University of Mexico (UNAM). Under that idea was that it was treated with antibiotics: “It was made like a plasticine mixed with antibiotics and it was put on the coral lesions.” But more recent research has begun to point to a virus, he explains.

Alvarez-Filip and his team analyzed a hundred points between July 2018 and January 2020. During that time they were able to record the rapid progress of this deadly disease along 450 kilometers of reef. In just a few months they began to see the corals covered with white spots, a sign that they had been dead for a short time. “Of the 29,095 colonies studied, 17% were already dead with signs of recent mortality,” says the scientific publication. In some species, according to the study, the mortality rate reached 94%, in others it was only close to 10%. The most affected were the Meandrina families, known as labyrinth corals, and the Faviidae, also called brain coral, with losses of up to 80% of the population.

At the moment, academics do not know how this disease, which was first registered in Florida eight years ago, was transmitted. The flow of ships or tourism are some of the theories that have not yet been proven. What they have been able to verify is the speed with which it is transmitted once it reaches a reef. “It is super contagious, it is the equivalent of the coronavirus. The covid is now known to be transmitted mainly through the air, this disease seems to be transmitted through water, which is the environment in which the corals are found and therefore it is highly transmissible, ”says Alvarez-Filip. The researcher points out that at the moment they have not been detected only in Banco Chinchorro, the most isolated barrier in the Mexican Caribbean.

Multiple species of corals in the Mexican Caribbean affected by the new disease.
Multiple species of corals in the Mexican Caribbean affected by the new disease.Lorenzo Alvarez-Filip

The impact is enormous for an ecosystem that was already being affected, says the study. Half of the coral species in the Caribbean are being affected by this disease and some, alert, face a high risk of extinction. Experts have found that sick corals produce 30% less calcium carbonate, the element that helps them build structures.

Eric Jordan, a UNAM scientist specializing in coral communities, assures that “SCTLD has been very impressive due to its aggressiveness, high severity and rapid lethality.” Unfortunately, he adds, “it is only the most recent event in the history of coral biota degradation by lethal disease.” For at least 40 years corals have been dealing with deadly emerging diseases that spread through the colony faster than the coral can grow. Jordan explains that it is due to the deterioration of the quality of the environment due to the effects of climate change and regional and local changes. “In just all the seas of the world, the environmental conditions are less and less suitable for corals,” he says.

Alvarez-Filip explains that the consequences that the deterioration of the reefs could have on society, mainly those who live on the coasts, are drastic. “Reefs form a natural barrier that protects coastlines from wave energy, storms and hurricanes. And this, in the long run, is going to destroy the barrier that protects us.” The loss of functionality of the corals also implies an impact on the fishing resources of the region, since the reefs provide refuge for a large number of fish.

The white syndrome has not yet reached some islands or coasts of the Caribbean Sea. The forecasts given by the experts, however, are not very encouraging. “Our prediction is that, if it reaches all those places, it will have mortality rates quite similar to what we reported here, which we also saw in Belize and Florida,” says the researcher. What remains to be done, he concludes, is to preserve the species as much as possible until they fully understand what they face when they face this new disease.

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