Marine ecologist and researcher Lorenzo Álvarez-Filip and his colleagues studied dozens of sites in the Mexican Caribbean in 2016 and 2017, before the outbreak and after it started, from 2018 to 2020.
They found what they described as an “unprecedented loss of corals”, according to the new study, published in the journal Communications Biology, showing the extent of the problem. Of more than 29,000 coral colonies assessed in the Mexican Caribbean region after the outbreak began, 17% were dead and 10% were infected.
It’s a “very aggressive” disease, Álvarez-Filip told The Washington Post, adding that once the coral is infected, it can die within weeks or even days. The living tissues of infected corals begin to disintegrate, sometimes losing their color. Of the 48 coral species recorded in the region, more than 20 have been affected – with variable mortality rates, some reaching 94%.
The disease has been found to affect several species that are important ecosystem builders – posing a threat to the ability of corals, which are animals, to build reefs, which provide habitats for other organisms, provide coastal protection and stimulate tourism.
While the disease is relentless and its origins not fully established, a key finding is that humans could be making it worse: more corals appeared to be getting sick near coastal development areas – around urban areas, hotels and tourist sites with pollution and runoff, says Álvarez-Filip.
He gave an example: if you go to a hospital where the underlying conditions are good, you are more likely to recover. For reefs, pollution is an aggravating problem, making disease more difficult to control. “The problem is that everything changes,” Álvarez-Filip said.
Robert H. Richmond, director and research professor at the University of Hawaii at the Kewalo Marine Laboratory in Manoa, said the region, including the Caribbean, Florida and Mexican coasts, has recently experienced a ” triple whammy: violent hurricanes that can topple or smother corals, coral bleaching linked to climate change and high seawater temperatures, and now the spread of disease.
“It was kind of an insult and a hurt on top of the insult and the hurt,” he said. “It has driven these coral reefs and these populations to the point where they are no longer able to sustain themselves. … They were decimated. And it’s kind of a downward spiral.
Corals, Richmond said, require sufficient density to perform their elegant spawning once a year, which is indicated by the lunar cycle. They simultaneously release eggs and sperm – gametes – into the water. Since the corals are unable to move, their gametes float to the surface of the water, fertilize, and then sink back down to begin growing into new coral.
“As corals die and the distance between living colonies increases, the chances of spawning events occurring in succession drops precipitously,” Richmond said.
Populations of some species are so low and their ability to reproduce is so compromised by changing environmental factors, including water quality – suffering from a “rogue chemical gallery” from the outfalls of sewers – that there is little hope for recovery without some form of human intervention, he says.
Although stopping the spread of the contagious disease is difficult, Álvarez-Filip said efforts are underway, including restoring reefs, preserving genetic material and administering probiotics to increase resilience. .
But “these efforts will only succeed if we change the regional conditions,” Álvarez-Filip said. “We can put a lot of effort, a lot of money into trying to save and restore the coral,” he said. “But in the end, if we still have climate change, we still have deforestation; we still have pollution.
Coral health can be compared to that of a bank account, with live corals being the main focus and reproduction the focus, Richmond said.
“If you put corals back in an area of poor water quality next to an urbanized area, you’re essentially putting them in a bank account that not only has no interest, but has high monthly fees,” did he declare. “Nothing that is produced there will eventually receive a population, and eventually those corals will die and need to be replenished. And so you go bankrupt.