A diver observes a coral reef in the Mexican Caribbean.Lorenzo Álvarez-Filip
A new disease has become the final executioner of the Mexican Caribbean’s corals. The eruption, first identified in Florida in 2018, reached shores of Mexico at least four years ago. Since then it has continuously devastated the reefs of the Riviera Maya. A study published this Thursday in the journal Nature shows that the disease has affected at least 21 species of coral, some of which have been classified as structural to help maintain the functionality of those ecosystems. At least 17% of corals analyzed in more than 29,000 colonies died from this condition. The authors say it’s probably the “deadliest on record in the Caribbean.”
White Syndrome or Hard Coral Tissue Loss Disease (SCTLD). Those are the Spanish names for this new state that besieges the second largest barrier reef in the world, the Mesoamerican reef system, and about which little information is yet available. Initially, a bacterial infection was thought of, says Lorenzo Alvarez-Filip, author of the study and researcher at the Institute of Marine Sciences and Limnology at the National Autonomous University of Mexico (UNAM). Under this idea, it was treated with antibiotics: “It was made like plasticine mixed with antibiotics and applied to the coral lesions.” However, more recent research suggests it may be 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 progression of this deadly disease along 450 kilometers of reef. In just a few months, they began to see the corals speckled with white, a sign that they had been dead for a short time. “Of the 29,095 colonies examined, 17% were already dead with evidence of recent mortality,” reads the scientific publication. According to the study, the mortality rate for some species reached 94%, while for others it was just under 10%. The hardest hit were the Meandrina families, known as labyrinth corals, and the Faviidae, also known as brain corals, with population losses of up to 80%.
Scientists do not currently know how this disease, which was first recorded in Florida eight years ago, was transmitted. Shipping or tourism are some of the unproven theories. What they have been able to verify is the speed at which it is transmitted once it reaches a reef. “It’s super contagious, it’s the equivalent of the coronavirus. It is now known that the Covid is mainly transmitted through the air, this disease appears to be transmitted through water, which is the environment in which the corals are found and is therefore highly transmissible,” says Alvarez-Filip. The researcher points out that at present they have not only been detected in the Banco Chinchorro, the most isolated barrier in the Mexican Caribbean.
Several coral species in the Mexican Caribbean are affected by the new disease.Lorenzo Álvarez-Filip
The impact is huge for an ecosystem that has already been affected, the study said. Half of the coral species in the Caribbean are affected by this disease, and some are vigilant and endangered. Experts have found that diseased corals produce 30% less calcium carbonate, the element that helps them build structure.
Eric Jordan, a UNAM scientist specializing in coral communities, assures that “SCTLD was very impressive because of its aggressiveness, high severity and quick lethality”. Unfortunately, he adds, “this is only the latest in the history of the destruction of coral biota by deadly diseases.” For at least 40 years, corals have struggled with deadly diseases that spread through the colony faster than the coral can grow . Jordan explains that this is due to the deterioration in environmental quality due to the effects of climate change and regional and local changes. “Simply in all the seas of the world, the environmental conditions are becoming less and less suitable for corals,” he says.
Alvarez-Filip explains that the consequences that reef degradation could have on society, especially those living along the coasts, are drastic. “Reefs form a natural barrier that protects shores from wave energy, storms and hurricanes. And that, in the long run, will destroy the barrier that protects us.” The loss of coral function also implies an impact on the region’s fish stocks, as the reefs provide shelter for many fish.
White syndrome has not yet reached some islands or coasts of the Caribbean Sea. However, the experts’ forecasts are not very encouraging. “Our prediction is that by the time it gets to all of these places, it’s going to have death rates quite similar to what we’ve reported here, which we’ve also seen in Belize and Florida,” says the researcher. He concludes that there remains work to be done to conserve the species as much as possible until they fully understand what to expect when confronted with this new disease.
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