Between 2018 and 2019, a rare disease known as 'White Syndrome' wiped out hundreds of coral colonies in the Mexican Caribbean, the same number as lost in 40 years, bringing some species to the brink of local extinction.
The facts are alarming for the scientific community, as it is the deadliest disease for corals since it has been recorded.
In a desperate search for solutions, scientist Anastazia Banaszak, from the Institute of Marine Sciences and Limnology of the National Autonomous University of Mexico (UNAM), is leading an ambitious project to guarantee the survival of endangered coral species: the cryopreservation of their sperm.
The technique consists of freezing male reproductive cells in corals indefinitely, in order to reproduce them in a laboratory and do future restoration work, he explained in an interview with Causa Natura Journalism.
The reefs of Quintana Roo are part of the Mesoamerican Reef System, one of the largest coral reefs in the world, which extends for more than 1,400 kilometers parallel to the Caribbean coasts of Mexico, Belize, Guatemala and Honduras, home to hundreds of marine species, many of them of commercial interest.
Corals, the main reef formers, are colonial animals, made up of a calcium carbonate rock base covered by small organisms called 'polyps', inside which they live in microalgae called zooxanthellae, which give them those attractive colors.
Bananzak explains that massive corals in their natural environment reproduce sexually. On certain days of the year, according to the Moon's cycle, a male colony releases gametes (sperm) and a female colony releases eggs. In the environment, they come together and form a 'coral larva', which attaches to the seabed and begins its growth process, which involves dozens of years.
However, the massive loss of coral colonies, which has left colonies isolated, makes natural reproduction practically impossible for many species.
The first assisted reproduction experiments were carried out before 2018 with colonies of a species of brain coral (Diploria Labyrinthiformis).
“We were working with a small population of 12 colonies. We collected their sperm and eggs and crossed them, and from that we obtained new corals, their little children, so to speak. But then came the disease (White Syndrome) and we started freezing sperm. After 3 years, of the 12 we had, only two are left alive, but we have frozen sperm from the rest,” he explained.
The Laboratory of the Reef Systems Unit of the ILCM is the only one in Mexico that has developed this technique, which is similar to that of preserving human sperm with freezing methods.
With this, he said, it is possible to reproduce new corals and repopulate the reef in the future.
Since the first pilot project, 100 new corals have been reproduced and planted in the Puerto Morelos Reef National Park, but for now, said the academic, efforts are to preserve sperm until the disease has disappeared from the region, to guarantee their growth.
“Sperms can be preserved for many years, indefinitely, which will allow us to have genetic material to reproduce in 10 or 100 years, even when combined with eggs from coral colonies in other regions,” said the specialist in phytobiology.
According to data from the UNAM Biodiversity and Reef Conservation Laboratory, among the species most impacted by White Syndrome are pillar coral (Dendrodyra Cylindrus) and labyrinth coral (Meandrina ssp), with population losses of 98 and 94 percent, respectively.
This means that the few colonies of these species that still exist are isolated from each other, so that their natural reproduction is impossible.
Another way to reproduce corals is through fragmentation, which consists of cutting a fraction of the coral and placing it elsewhere to grow as a new colony, but this technique has one limitation: there is no genetic diversity, said Bananzak, also a member of the Coral Restoration Consortium Steering Committee, a community of international experts focused on ensuring that corals survive the 21st century and beyond.
“When you do this thing of seeding fragments or microfragments or nano fragments, you are taking a colony, breaking it into pieces and seeding. These aren't new corals, they're clones. What we do takes longer, but the advantage is that each colony is genetically different,” he said.
Organisms of any species, he said, can only adapt to changes in their environment through genetic diversity.
“It's like with humans, we're genetically different. With Covid-19, some are more resistant than others. What if they are all genetically the same? If a disease comes along that kills one, then it will kill everyone. The same thing happens with corals,” he added.
“Without reefs there is no life in coastal communities”
Coral reefs are important ecosystems because of the multiple environmental services they provide, which make life possible in coastal communities.
According to María del Carmen García Rivas, director of the Puerto Morelos Reef National Park, among the services provided by reefs is coastal protection, as they prevent beach erosion and serve as a containment barrier against intense weather events, such as hurricanes. Corals, like trees or mangroves, are carbon dioxide (CO2) collectors.
They are the habitat of different marine organisms, some of them important for fishing and the beauty of their landscapes is an important tourist attraction, contributing to the local economy.
In addition, the white sand that characterizes the beaches of the Mexican Caribbean, and which give the water a turquoise blue hue, is composed of microfragments of coral skeleton.
“Without reefs, life is not possible in coastal communities. It gives us protection, food and natural beauty, the engine of the region's economy,” he said.
However, the increasing pollution resulting from the poor disposal of wastewater, the excessive use of sunscreen by tourists and plastic waste - associated with tourism and real estate growth - as well as external factors such as global warming and sargassum, represent a latent risk for corals.
García Rivas proposes a halt to tourism and real estate development in the region until there are growth conditions friendly to nature.
For his part, Lorenzo Ávarez Filip, from the Laboratory of Biodiversity and Reef Conservation, indicated that the coral population in the Mexican Caribbean has been seriously decreasing for 50 years.
“During the seventies, a disease, the 'White Band' (other than White Syndrome) killed more than 90 percent of the corals of the elk horn species (Acropora Palmata). This was the first major tragedy reported. Since then, it's been 5 decades, what we've had is a consistent loss,” he said.
In 2014, White Syndrome was detected for the first time off the coast of Florida. In the summer of 2018, it was identified off the Mexican coast and has spread to practically the entire Caribbean region, Álvarez Filip said.
It is characterized by the rapid loss of living tissue, that is, polyps that cover the base of calcium carbonate. In a matter of two weeks, it could cause the death of colonies that took more than 100 years to form.
“It has been the most virulent and most aggressive disease that has ever occurred on corals, for 2 main reasons, because it kills much faster than other diseases and because it affects a greater number of species. In this case, more than 25 of the 40 that exist in the Mesoamerican Reef,” he explained.
Lorenzo Álvarez Filip argued that, at this rate of mortality, we can talk about a scenario in which there will be no more living corals at the regional level for a couple of decades, with the economic and social implications that this entails.
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