Hondurast Gusigalpa — A mysterious, highly contagious and deadly disease is spreading through coral reefs in the Caribbean Sea, shocking scientists and leaving a string of skeletons in its path.
As it advances from Florida into the far reaches of the Caribbean Sea, it threatens to wipe out much of the hard corals across the ocean, destroying coral reefs and the marine life they support for future generations. Environmental destruction will also disrupt the lives of millions of people in coastal communities who depend on coral reefs for food or jobs.
Gabriela Ochoa, project manager at the Roatan Marine Park in the Gulf Islands of Honduras, described the rapid spread of the disease: "It's basically like a coral coronavirus. Affecting more than 20 species of hard corals, stony coral tissue loss disease (SCTLD) threatens slow-growing coral reefs and their fragile ecosystems.
"The only difference is that the mortality rate from COVID can't even be compared to what we see in coral reefs," Ochoa added. In some coral species, the mortality rate is as high as 100%.
While other, more well-known factors such as pollution and climate change have led to a decline in coral cover in the Caribbean by about 60 percent over the past three decades, the new disease is killing corals at a faster rate.
Once a colony is infected, death comes quickly. "You could lose centuries-old colonies in just a few weeks or months," said Melina Soto, coordinator of the Mexico Healthy Coral Reef Initiative.
SCTLD was first discovered off the coast of Florida in 2014 and has since infected about half of the state's coral reefs. The reason is unknown, but humans may be the culprit.
The theory splits along two main tracks. The first is factors such as climate change and rising sea temperatures, as well as pollutants such as untreated sewage and even sunscreen that reduce the resilience of coral reefs, making corals vulnerable to existing bacteria. The second center revolves around the idea that the emergence of new pathogens is the result of human activity.
In the end, the answer could be all of the above. "Just like COVID, when you have other health problems, when you get COVID, your risk is higher," Ochoa said.
Over the past seven years, the disease has spread to the Caribbean, often traveling against the current, suggesting that pathogens may reach new areas by attaching to ships. "The point that is almost always repeated is that the first cases were found near the port," Soto said.
In 2018, SCTLD was discovered off the coast of Puerto Morelos, Mexico, between the Cancun tourist hotspot and Playa del Carmen near the northern tip of the Central American Reef, the world's second largest coral reef. Since then, the disease has spread hundreds of miles along the hard coral masses of the reef, all the way to the southernmost tip around the Honduran Gulf Islands, where it was first detected in September 2020.
Brain corals are most affected by the Healthy Coral Reef Initiative, a disease that brings a rare species of columnar coral to the brink of extinction. The first sign of coral infection is the appearance of small foci in which there is no tissue or skin, exposing bones. As the disease progressed, all the tissues of the coral were stripped away, leaving only a dead skeleton.
Once an infection has emerged, the disease spreads from the coral to the coral in the reef system, or jumps from the infected site to the healthy site through fish or divers.
Mitigating this impact is a costly and almost insurmountable task. The antibacterial cream applied to the lesion site has had some success in stopping the infection, but it has no immunity to subsequent infections, and this application is very laborious and expensive.
Instead, the organization is building coral nurseries in water tanks on land to conserve genetic diversity and nurture new species with a view to restoring coral reefs in the future. But at a rate of a few centimeters per year, a full recovery can take hundreds or even thousands of years.
Soft corals, such as elegant fan-shaped corals that sway with the flow of water, are not affected by SCTLD. But the loss of hard corals is not just about their genetic diversity.
Hard corals are "reef builders" and are essential for the formation of coral reefs. As hard corals die, they are eroded and compacted, reducing the reef's protection from coastal erosion, flooding and hurricane storm surges. Declining coral cover has also led to habitat loss for marine wildlife, including about 1,500 species of fish.
The damage to Central American coral reefs and other parts of the region will have an impact beyond the ocean. "If we don't have corals, then we don't have all the other stuff associated with them," Ochoa said. Coral reef-related tourism alone generates about $8 billion a year in revenue for Caribbean economies.
Although there have been large-scale coral deaths in the past, as well as other diseases affecting coral reefs, the damage caused by SCTLD is unprecedented. "We've never seen 23 different kinds of corals get sick at the same time," Ochoa said.
In many places, coral cover has been reduced to half of what it was before the disease arrived, and algae are taking over. What was once brilliant and colorful colors now become dull and green.
The spread of this contagious and deadly disease heralds a similar fate for Caribbean coral reefs. "Coral reefs as we know them will no longer exist," Ochoa said.