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A deadly disease is wiping out Caribbean coral, researchers find

Footage from 2018 and 2019 off the coast of Mexico shows coral affected by stony coral tissue loss disease, which has spread across the Caribbean. (Video: Lorenzo Álvarez-Filip)
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A regionwide outbreak of coral disease in the Caribbean is killing off up to 94 percent of some coral species in what researchers say could become the “most deadly [such] disturbance ever recorded” in the area, according to findings published Thursday.

Stony coral tissue loss disease, first reported off Florida in 2014, has rapidly spread, diffusing across the Caribbean. The waterborne disease, researchers say, probably is made worse by coastal development and climate change — and human intervention probably is necessary to prevent regionwide extinction of some species.

Marine ecologist and researcher Lorenzo Álvarez-Filip and colleagues surveyed dozens of sites in the Mexican Caribbean before the outbreak, in 2016 and 2017, and after it began, in 2018 to 2020.

They found what they described as an “unprecedented loss of corals,” according to the new study showing the extent of the problem, published in the journal Communications Biology. Of more than 29,000 coral colonies assessed in the Mexican Caribbean after the start of the outbreak, 17 percent were dead and 10 percent were infected.

It’s a “very aggressive” disease, Álvarez-Filip told The Washington Post, adding that once coral is infected, it can die within weeks, even days. The infected corals’ living tissue begins to disintegrate, sometimes losing color. Of 48 recorded coral species in the area, more than 20 were affected — with varying mortality rates, some as high as 94 percent.

The disease was found to affect several species that are important builders in the ecosystem — posing a threat to the capacity of corals, which are animals, to build reefs that provide habitats for other organisms, offer coastal protection and drive tourism.

While the disease is relentless and its origins are not fully established, a key finding is that humans could be making matters worse: More corals appeared to become sick near areas of coastal development — around urban areas, hotels and tourism spots with pollution and runoff, Álvarez-Filip said.

He offered an example: If you go to a hospital where the underlying conditions are good, it’s more probable that you will recover. For the reefs, pollution is a compounding problem, making diseases harder to kick. “The problem is that everything is changing,” Álvarez-Filip said.

Robert H. Richmond, the director and a research professor at the University of Hawaii at Manoa’s Kewalo Marine Laboratory, said the wider region, including the coasts of the Caribbean, Florida and Mexico, has recently experienced a “triple whammy”: severe hurricanes that can topple or smother coral, coral bleaching tied to climate change and elevated seawater temperatures, and now the spread of disease.

“It was kind of insult and injury on top of insult and injury,” he said. “It’s driven these coral reefs and populations to the point where they’re no longer capable of self-sustaining. … They’ve been decimated. And it’s kind of a downhill spiral.”

Corals, Richmond said, require sufficient density to carry out their elegant once-a-year spawning, which is cued by the lunar cycle. They simultaneously release eggs and sperm — gametes — into the water. As corals are unable to move, their gametes float up to the water’s surface, fertilize, then drop back down to begin growing into new coral.

“As corals die and the distance between living colonies increases, the chance of spawning events succeeding drops precipitously,” Richmond said.

Some species’ populations are so low, and their ability to reproduce so compromised by changing environmental factors, including water quality — suffering under a “rogue’s gallery of chemicals” from sewer outfalls — that there is little hope for a recovery without some form of human intervention, he said.

Although it would be difficult to stop the spread of the contagious disease, Álvarez-Filip said efforts are underway — including reef restoration, the preservation of genetic material and the administration of probiotics to increase resilience.

But “these efforts will only succeed if we change the regional conditions,” Álvarez-Filip said. “We may invest a lot of effort, a lot of money to try to rescue and restore coral,” he said. “But at the end, if we still have climate change, we still have deforestation; we still have pollution.”

The health of corals can be likened to that of a bank account, with live corals as the principal and reproduction the interest, Richmond said.

“If you put corals back into an area of poor water quality next to an urbanized area, you’re basically putting it into a bank account that not only has no interest but has a high monthly fee,” he said. “Nothing that’s produced there is going to end up receiving a population, and, eventually, those corals are going to die and need to be replenished. And so you go bankrupt.”