As record coral bleaching swept across the Caribbean over the past two years, scientists rushed to save the reefs using tools like multivitamins, artificial intelligence and underwater speakers. But the scale of the crisis is outpacing their efforts, according to a yearlong investigation by journalists at The BVI Beacon and in five other countries and territories. This story is part two in a series.
For more than a decade, Mariane Aimar-Godoc regularly laboured underwater, collecting coral eggs by moonlight to raise in nurseries and transplant back onto degraded reefs.
As director of the non-profit Guadeloupe Initiative for the Restoration of Marine Ecosystems (IGREC Mer in French), her work helped pioneer one of the Caribbean’s most ambitious marine restoration projects.
Then the ocean turned against her.
In 2023, an unprecedented marine heatwave swept over the region, bleaching wide stretches of coral and devastating the reefs she had spent years trying to rebuild in Guadeloupe. The heat, which grew worse in 2024, forced her team to halt much of its restoration work.
“When it’s too hot, the corals don’t spawn anymore,” she said. “And when the water is too hot, the corals that we have raised, either in marine nurseries or in aquarium nurseries, we can’t replant them in the sea.”
Instead, they devised an emergency plan to evacuate vulnerable corals to land-based nurseries — an effort they dubbed “Noah’s Ark.”
“It might give time for researchers around the globe, say, to work on the development of ‘super corals’ that would be more resistant to warmer water temperature,” Ms. Aimar-Godoc said. “So we are trying to do research in all directions to find solutions and try to save what we can still save.”
Racing the heat
The Noah’s Ark proposal is one of dozens of innovative experiments unfolding across the Caribbean, where coral scientists are racing against time.
Reef restoration, once an obscure discipline, has become an increasingly common response to an underwater ecological crisis.
As reefs decline under pressure from global warming, pollution, overfishing and coastal development, scientists have also doubled down on other wide-ranging solutions.
Some are educating the public, repopulating reefs with key wildlife, or diving in to scrape harmful algae off coral heads by hand.
Others are deploying cutting-edge technologies, including gene editing, artificial intelligence, multivitamins, underwater acoustics, and more.
But the efforts remain fragmented. Much of the work is spearheaded by small non-profits and academic labs patching together short-term grants.
All of this is happening at a time when international aid to confront the climate crisis is weakening and wealthier nations are scaling back their financial commitments, leaving these teams with limited support in the face of a global environmental emergency.
Meanwhile, the stakes are escalating. Over the past two years, record temperatures triggered mass bleaching — a potentially fatal condition caused when heat-stressed corals eject the colourful symbiotic algae that live in their tissue and provide much of their food.
Scientists now say that the world has been experiencing the fourth, and most extensive, global coral bleaching event on record. And it may not be over yet.
‘Only 12 of us’
Like many researchers, the team at IGREC Mer in Guadeloupe has struggled to keep up with the crisis.
Ms. Aimar-Godoc said her group’s “Noah’s Ark” technique has been used on a large scale to preserve corals on the Great Barrier Reef off Australia.
But scaling it up in the French Caribbean requires far more support.
“Our job isn’t to transplant corals on a massive scale everywhere,” she said. “There are only 12 of us in the whole of Guadeloupe, so we’re not going to change the world. Our job is to develop techniques, experiment with them, validate them, and send them to local decision-makers.”
To that end, the non-profit applied last year for a grant from the Guadeloupe regional government. The proposal passed initial review, but the team is still waiting for a final decision.
“We’re waiting to hear whether this year, in 2025, we’ll have the funding to be able to set this up on a large scale,” she said.
Remote-sensing tech
Roughly 250 miles northwest of Guadeloupe, the United States Virgin Islands has emerged as another regional leader in coral innovation.
Across 90 acres of reefs off the island of St. Croix, The Nature Conservancy is heading up one of the Caribbean’s largest coral restoration projects with support from the US National Oceanic and Atmospheric Administration and National Fish and Wildlife Foundation.
During the recent bleaching, the team deployed remote-sensing techniques to help identify heat-tolerant coral most likely to survive future ocean warming.
“We can bring [the corals] into our lab and do some additional testing and say, ‘Okay, these ones did really well through that,’” said Jessica Ward, the USVI Coral Program director for The Nature Conservancy. “So these are the ones that we want to double down on and propagate for our work.”
At a land-based nursery, which houses up to 15,000 coral fragments, the researchers condition coral to build up its heat tolerance. Tanks are kept at 83 to 84 degrees Fahrenheit in the winter and gradually warmed through summer, said aquaculture supervisor Javier Soler.
“It’s important for us to do that, because if they aren’t getting stressed, they won’t remember thermal tolerance as a trait,” Mr. Soler said, adding, “We are hoping to push to 87 degrees for two to three months this year with the better water quality conditions. Once you hit 88 degrees, metabolic functions break down, so 87 is our limit.”
To mimic natural reef conditions and keep the coral healthy, Mr. Soler also adjusts the system’s lighting and supplements the water with raw calcium carbonate.
On the neighbouring island of St. Thomas, Coral World Ocean and Reef Initiative’s land-based coral nursery uses seawater in raceway tanks.
“When we have these big heating events, we are subjecting the corals in our raceways on land to those warmer waters, and then when it cools down, it cools down in the raceways as well,” said Sam Eliades, the initiative’s associate director.
The setup means that corals raised in captivity experience the same extreme temperature swings as those in the ocean — a kind of stress test for survival.
“Corals that are able to survive through these heating events in our care, we feel are really well positioned and well prepared to be the ones that we want to restore,” Mr. Eliades said.
Multivitamins for coral
Some scientists are looking beyond raising heat-tolerant corals, focusing instead on helping existing reefs survive stress.
Like humans, corals need nutrients. That’s the premise behind a project led by Colleen Hansel, a senior scientist at the Massachusetts-based Woods Hole Oceanographic Institution (WHOI).
Working in Massachusetts and St. Thomas, Ms. Hansel has developed a coral “multivitamin” designed to strengthen immunity by delivering key trace metals like manganese, zinc and selenium.
“There’s really not a lot of these vitamins and trace metals just floating around in the water that they can access when they start to be stressed,” Ms. Hansel explained. “So then the symbionts living in the coral tissue and the coral animal themselves are fighting over these limited resources.”
Ms. Hansel’s lab devised two delivery systems: a donut-shaped ring that encircles out-planted coral plugs and a paint for ceramic tiles where coral larvae settle.
Lab tests suggest the vitamins help coral resist heat stress, Ms. Hansel said.
But translating that success to the open ocean has been more difficult: A 2024 field test off St. Thomas was destroyed during an active hurricane season.
“There is that sense of urgency, but then as scientists we’re trained to be very critical of our own work and critical of our science,” Ms. Hansel said. “You’re walking this fine line of, ‘Okay, I have this idea. I want to implement it, but I want to do it responsibly.’”
A second deployment has been planned to coincide with the installation of a new artificial reef off the island’s coast.
Making a healthy noise
While Ms. Hansel focuses on feeding corals, her colleague has been serenading them.
Aran Mooney, who heads WHOI’s Sensory Ecology and Bioacoustics Lab, uses sound to lure coral larvae onto degraded reefs in the USVI.
Healthy reefs, he said, produce a rich soundscape: the clicks from snapping shrimp, the grunts of fish, and even distant whale calls. Coral larvae use these audio cues to choose where to settle.
Since 2012, Mr. Mooney has recorded thriving reefs at Tektite Bay off St. John’s southern coast. He now uses these recordings to operate the Reef Acoustic Playback System (RAPS) — underwater speakers that play healthy reef sounds across degraded areas to attract coral larvae.
Sounds of a reef
Click above to hear the sound of a healthy reef that WHOI scientists recorded at Tektite Bay off St. John’s southern coast in the United States Virgin Islands. Click below to hear 15 seconds recorded at a degraded reef off St. John followed by the same reef after WHOI scientists added their Reef Acoustic Playback System (RAPS).
Early results show promise, he said: In experiments, two types of coral larvae settled faster within a 36-hour window when exposed to the sound. Typically, coral larvae take between two and six days to settle on a substrate, but depending on the species, some may take several weeks.
“We’re trying to integrate these methods to basically reproduce or regenerate some of these habitats and keep coral larvae coming back to these habitats and rebuilding them,” Mr. Mooney said.
A natural ally
Other scientists are taking a holistic approach to reef restoration by rebuilding the ecosystems that support coral.
In Puerto Rico, the non-profit Institute for Socio Ecological Research (ISER Caribe) has enlisted a natural ally: the long-spined sea urchin.
These spiky herbivores graze on algae that can smother coral if left unchecked. But after major die-offs in the 1980s and in 2022, urchin populations have declined dramatically across the Caribbean.
Although scientists were unable to determine precisely what caused the sea urchin die-off in the 1980s, the 2022 event was linked to a parasitic disease that spread rapidly and decimated the species.
To bring them back, the ISER team collects baby urchins from the water column and raises them in land-based tanks.
Once they’re larger and less vulnerable to predators, they’re released onto degraded reefs, said Stacey Williams, the institute’s executive director.
“We’re also going to be producing the herbivorous crab, because the crabs eat different species of algae compared to those sea urchins,” Mr. Williams said. “So we’re trying to be able to tackle all nuisance algae on the reef, and not have them just tailored to one species.”
Underwater AI
A similar effort is under way in the Virgin Islands, where an invasive algae called peyssonnelid algal crust, or PAC, has overrun many shallow reefs.
Oxford University marine biologist Bryan Wilson, who is working with the non-profit Association of Reef Keepers in the VI, believes that long-spined sea urchins eat the PAC.
To confirm the hypothesis, the team is monitoring urchins in underwater cages off the coast.
Coral biologist Bryan Wilson, left, and Association of Reef Keepers Managing Director Shannon Gore, right, erect an underwater cage to confine long-spined sea urchins for study off Frenchmans Cay in the Virgin Islands. (Photo: FREEMAN ROGERS | THE BVI BEACON)
The pilot project — backed by a grant of just over $20,000 from the United Kingdom government’s Darwin Plus programme — could pave the way for a larger-scale restoration campaign.
Lacking robust reef data in the VI, the team turned to technology to establish a baseline for the possible expansion. After filming 16 reef sites, Mr. Wilson’s research assistant used artificial intelligence to analyse the footage.
“She’s training this AI system to essentially tell us what’s on the reef,” Mr. Wilson said. “So she has to actually sit there and manually go through a photo and click, ‘coral,’ ‘sponge,’ ‘rock,’ ‘sand.’ When she’s done enough of that, it learns, and then it goes and it does them blind for us.”
The human threat
Researchers say coral restoration can’t succeed underwater alone: To give reefs a fighting chance, human pressures must also be addressed on land.
Such efforts are part of CoralCarib, a six-year project led by The Nature Conservancy in Jamaica, the Dominican Republic, Cuba and Haiti.
Backed by about $7.5 million from the German government, the initiative aims to identify and protect coral “refugia” — areas of reef more likely to survive in a warming ocean.
“Our interventions are not only meant to restore or rehabilitate the reefs that have been damaged, but also to identify the threats and to act against these threats with specific designs of abatement plans,” said biologist Aldo Croquer, the conservancy’s marine conservation programme manager for the central Caribbean. “Because we understand that if we do not reduce these threats that are common across the Caribbean, our chances of successful restoration are going to be hampered.”
Launched in 2023, CoralCarib has found that the most pressing threats include overfishing, coastal development, and declining water quality.
In Jamaica, one of the project’s partners is taking a community-based approach to addressing such pressures. About a decade ago, the Portland-based Alligator Head Foundation helped establish a six-square-kilometre marine sanctuary, where fishing is banned. Now, the foundation offers job training programmes for displaced fishers.
“They have been trained as lifeguards, they’ve been trained and certified as boat operators, and they have received other training and other skills that allow them to become employed in more sustainable long-term activities,” said Machel Donegan, the foundation’s executive director.
So far, he said, the programme has trained more than 75 people.
“The majority of the people who have benefited from the training and certification programmes, even if they are not employed, they’ve started to fish in other spaces,” Mr. Donegan said.
Still fighting
Despite the scale of the coral crisis, the people fighting to conserve and restore reefs still have hope.
In Jamaica, Haiti, Cuba and the Dominican Republic, the recent heatwaves dramatically set back the CoralCarib project by bleaching 90-95 percent of its coral nurseries, according to Mr. Croquer.
But his team has refused to give up.
“People came back quickly,” Mr. Croquer said. “People did not get depressed, or they did not abandon their projects. They stood up with more determination to continue.”
This investigation, the second instalment in the special series Corals: The Caribbean’s Silent Collapse, is the result of a fellowship awarded by the Puerto Rico Centro de Periodismo Investigativo’s Journalism Training Institute and was made possible in part with the support of Open Society Foundations.
