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SCTLD in Mexico: A slow-moving disaster

The Stony Coral Tissue Loss Disease is spreading throughout the northern part of the Mesoamerican Barrier Reef, affecting almost 20 different coral species. The challenge is to develop a disease management plan, says Dr. Anastazia Banaszak, local lead scientist of SECORE’s joint reef restoration project in the Mexican Caribbean.

Large pillar corals have been a poster child of the Puerto Morelos Reef National Park since its declaration in 1998. These majestic coral colonies may be centuries old. They form cathedral-like structures that allure fish and other marine creatures as well as attract thousands of tourists to come to the Yucatan Peninsula for snorkeling and diving. However, during the past few months, all of these impressive pillar coral colonies have died within weeks. They were killed by what marine scientists call the Stony Coral Tissue Loss Disease (SCTLD), a new lethal disease that was first reported in Florida in 2014 and is now spreading throughout the Caribbean.


Two pillar coral colonies infected and later killed by SCTLD. (Lorenzo Alvarez-Filip/UNAM -


“It is still unknown what causes this disease, but the endangered pillar coral seems to be particularly susceptible. Even huge colonies lose their tissue within a very short time and are covered by algae very quickly. At the end, all that is left is a dead, grey, fuzzy coral skeleton,” says Dr. Anastazia Banaszak, research scientist at the Reef Systems Academic Unit of the Universidad Nacional Autonoma de Mexico (UNAM) and local lead for SECORE’s research and reef restoration activities in Puerto Morelos.   

SCTLD is affecting about 20 coral species on the Mesoamerican Barrier Reef, which stretches over 1000 kilometers from the tip of the Yucatán Peninsula, México down to Belize, Guatemala and Honduras. “The situation is bad, and it is getting worse, because the disease seems to be slowly spreading southwards. Scientists and marine park managers have detected it all along the Mexican Caribbean,” Banaszak states.


An infected brain coral colony that lost all of its tissue only 25 days after this photo was taken. (Lorenzo Alvarez-Filip/UNAM -

Affected corals die very quickly

SCTLD has not been reported yet in Belize, but scientists don’t doubt that it has arrived there. “Close monitoring of the northern reefs of Belize is needed to spot SCTLD”, Dr. Banaszak reports. Furthermore, the spreading of the disease can be difficult to detect. “Here in Mexico, scientists and managers did not realize that the disease had spread to the Mesoamerican reef system at first. This is because the affected corals are dying fast, and because they are covered by algae so quickly it was really difficult to catch the disease in the act,” she says.


Recorded incidences of the Coral Disease Outbreak throughout the Caribbean (May 3, 2019) Source: Kramer, P.R., Roth, L. and Lang, J. 2019. Map of Stony Coral Tissue Loss Disease Outbreak in the Caribbean. ArcGIS Online. Check back frequently for updates to the map.


Mexican marine scientists and national park authorities have intensified monitoring of the Caribbean reefs since last summer and it is one of the main activities that needs to continue as agreed upon during an action meeting two weeks ago. Banaszak notes: “Although there is pretty much no funding available, the National Parks Commission is really working hard to do everything they can to combat the spread of this disease and to get everybody involved in this fight against the disease.”

To prevent the disease from spreading, scientists are applying methods which have been developed and tested in Florida, where SCTLD has so far affected 80 percent of the Florida Reef Tract. “In Florida, scientists studying the disease have teamed up with institutions and the public in a coordinated effort to attempt to stem the spread of SCTLD,” reports SECORE Research Director Dr. Margaret Miller.


UNAM scientist Dr. Anastazia Banaszak is the local lead of SECORE's joint reef restoration project in Puerto Morelos. (Sina Löschke)


While some scientists are working to find out what causes SCTLD – the culprit seems to be at least partly bacterial, as antibiotics can at least slow the disease – others are trying to treat affected colonies to prevent their complete mortality. They medicate diseased patches with a chlorinated epoxy resin that forms a physical barrier to isolate the affected area while the chlorine kills the microbes. Another approach to cure the coral is putting a gel enriched with antibiotics on infected patches. Scientists, managers, and aquarists in Florida are also teaming up to rescue some of the few remaining healthy colonies to bring them into captivity – hoping that these captive remnant populations can provide the source for future restoration material.

“Scientists and marine park authorities are using the experiences gained in Florida and are deploying these methods here in Mexico as well. Sometimes the interventions work, sometimes they don’t, but at least people are trying everything possible and are working hard on finding out what causes this slow-moving disaster – and we see similarities to the situation in Florida,” Anastazia Banaszak says.


Is cryopreservation the best way out?

During the action meeting, the Mexican scientists and marine park authorities also discussed what could be done to rescue coral colonies and secure the reefs’ genetic diversity in captivity. “Should we collect any living tissue that is left from highly susceptible species such as the pillar coral or the elliptical star coral and try to keep it alive in culture systems, like our colleagues in Florida are doing in an almost heroic rescue effort? Or should we focus on isolating the corals’ genome and cryopreserve it for future restoration? Those were two of the many questions discussed”, reports the UNAM scientist.

From the current perspective, cryopreserving coral tissue, sperm, eggs, and larvae seems to be an important option. Anastazia Banaszak: “For banking coral genetic resources in land-based tank systems, one would need facilities whose water system is not connected to the ocean, since SCTLD is in the water and spreads with the currents.“ Furthermore, a colony rescued from the reef might look healthy but could be carrying the pathogen and therefore infect all colonies kept in the nursery. “It is a pretty dire situation. The only good news so far is that the reef-building Acropora species don’t seem to be affected,” Anastazia Banaszak says and adds: “The final consensus is that we need to try all of these techniques. Fortunately, here in UNAM we have gained experience over the past few years with cryopreservation of coral sperm, eggs and larvae. We´ve had a fair bit of success. Some of the sexual recruits that we outplanted last year were produced from cryopreserved sperm. So, we are very excited about using this in future restoration efforts.”



One of the many infected coral colonies that UNAM scientist Lorenzo Alvarez-Filip and his colleagues from UNAM's Barcolab have been documenting in the northern part of the Mesoamerican reef system since July 2018. (Lorenzo Alvarez-Filip)

Most of SECORE’s joint reef restoration work in Puerto Morelos has been done using larvae of elkhorn and staghorn corals (Acropora palmata / Acropora cervicornis). But scientists still need to figure out if the mass outplanting of Acropora fragments or settlers would improve or aggravate the situation for SCTLD affected corals. “Those precautionary concerns have been the reason why a lot of outplanting activities had been slowed during the past two to three years in Florida. We here in Puerto Morelos also need to think about the possible outcome for affected species and will handle our restoration activities very carefully”, Anastazia Banaszak says.


Learning from Florida’s unfortunate precedent

However, Mexican scientists and national park authorities want to save time and benefit from the experiences and progress made in Florida. “Science and institutions in Florida have a management plan that enables them of coordinate all players and make precautionary efforts. Mexico should take this as a good example and develop its own management plan”, says Anastazia Banaszak.

Sharing information is another aspect. In Florida, for example, research has examined effective means for decontaminating water sports gear or equipment to prevent spread of known coral pathogens. “Those protocols should be shared with dive shops, hotels and research stations all around the Caribbean, because people love to travel and dive among the best reef sites. Equipment that has not been decontaminated could accelerate the transfer of pathogens from an infected area to a pristine reef sites,” Margaret Miller says. To win the battle against SCTLD Caribbean coral reefs need all the help they can get. (Find more information about the decontamination your gear here)

Sina Löschke

The following video was provided by Dr. Lorenzo Alvarez-Filip. It gives a closer look at the SCTLD outbreak off the northern Caribbean region of the eastern Yucatan peninsula, Mexico. 



For more background information on SCTLD watch the following webinar, provided by the Reef Resilience Network:




Further resources: 

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