This deadly coral disease is threatening more than just reefs

Two years ago, Alizée Zimmermann could hardly name more than a few species of coral. But as a native of Turks and Caicos and a scuba instructor with thousands of dives under her belt, she knew something was wrong when she saw some of the islands’ oldest and largest corals disintegrating before her eyes.

“I saw a 20 foot tall pillar coral, probably two-, three-hundred years old, just peeling like if someone had poured acid over it,” she described later. She said her eyes welled with tears. “It was apocalyptic.”

She began taking pictures of the white lesions that appeared to be eating away the corals’ flesh and sent the photos to experts. Their diagnosis: stony coral tissue loss disease, which kills at least two-thirds of its hosts within months, if not weeks. First detected off the coast of Florida in 2014, it’s since ravaged more than 30 hard coral species in at least 17 countries and territories in the Caribbean. In South Caicos, researchers from the School for Field Studies have reported a 62% loss of live hard coral coverage at three long-term research sites since the disease was first detected there in 2019.

Stony corals’ rigid external skeletons are what give structure to reefs, which in turn provide the backbone to the area’s tourism industry. In a typical year, more than a million tourists flock to Turks and Caicos to experience its white sands, turquoise waters, and coral reefs, drawing in about $80 million annually, according to a 2018 report co-published by Eftec (economics for the environment) and the Joint Nature Conservation Committee. Hotels and restaurants alone account for nearly 40% of the islands’ economy. Those took a huge hit in 2020 due to COVID-19, but travel is already starting to rebound. From January to April of this year, the islands saw a 96% increase in international passenger arrivals, according to the Turks and Caicos Tourist Board.

Coral reefs support much more than tourism. They also provide habitat, nurseries, and feeding grounds for at least a quarter of all marine species, making them a crucial component of the global fishing industry. And in an era when more frequent and severe tropical storms threaten the small island nation, reefs provide critical storm surge protection. Just how much isn’t known, but in the U.S., for instance, they prevent approximately $1.8 billion of damage each year.

Unlike most coral diseases which tend to fluctuate with seasonal temperature changes, this one shows no sign of fizzling out. Plus, it’s spreading. Unless extraordinary precautions are taken, there’s a good chance the disease will eventually reach the Pacific Ocean, said Judith Lang, scientific coordinator of the Atlantic and Gulf Rapid Reef Assessment Project. Limited lab experiments have already shown that some Pacific coral species may be susceptible to the disease.

“The disease is still chronically present in the original population the exact same way that they say COVID will now be in the human population,” Lang said.

The potential consequences of the disease reaching the Pacific could be “severe,” said Caroline McLaughlin, Florida Sea Grant’s national coral disease coordinator. The Pacific reefs are some of the healthiest and most biodiverse in the world. “They are incredibly important ecologically, economically and culturally,” McLaughlin said. Already she’s helping prepare potentially vulnerable U.S. jurisdictions in the Pacific, including Guam, American Samoa, and the Northern Mariana islands, for the worst. “The best time to invest resources, prepare and plan is now.”

What sparked the initial outbreak in Florida is a mystery — toxins, bacteria, and viruses are all potential culprits. “We’re likely never going to be able to say what was the one thing that caused it,” said Maurizio Martinelli, Florida Sea Grant’s coral disease response coordinator. “But it was a period of particular stress for corals in Miami.”

In 2014, a large-scale dredging project at the port of Miami was disrupting local reefs. That same year, an unprecedented ocean heat wave instigated a worldwide coral bleaching event, which can increase corals’ susceptibility to disease.

How the disease spread from Florida to the Caribbean is also a source of bafflement. It was four years before the disease was detected in Jamaica in February 2018. Soon after, reports came in from Mexico and Sint Maarten. By the following year, St. Thomas, Dominican Republic, Turks and Caicos, Belize, St. Martin, St. Eustatius, Puerto Rico, and the Bahamas had all been infected.

The one thing that’s clear, according to Lang, is that humans were involved. “There was no way that it could get from Florida just through the water in the currents that exist naturally,” she said.

Whatever is behind the disease, the consequences of not stopping it would be dire. White band disease, first detected in the 1970s, eventually killed 80% of reef-building elkhorn and staghorn corals, which once provided critical habitat for marine life in the Caribbean. Stony coral tissue loss could result in comparable devastation, according to Lang.

Researchers have homed in on the $176 billion global shipping industry as a possible culprit. Ballast water, which ships routinely take on and discharge to maintain stability as they on and offload cargo, has already been proven to be responsible for transmitting invasive species such as zebra mussels, as well as bacteria including Vibrio and E. coli.

As a precautionary measure, the U.S. Coast Guard issued a two-page bulletin in September 2019 reminding commercial vessels of mandatory ballast water practices and additional voluntary recommendations to mitigate the potential spread of the disease. One of the primary requirements is that ships conduct ballast water exchanges at least 200 nautical miles offshore in most cases. According to the document, some are conducting such exchanges as close as 12 nautical miles out.

Today, Zimmermann is executive director of the Turks and Caicos Reef Fund, leading disease response efforts in a region where economic viability is intrinsically linked to its natural resources. She spends her days setting up mooring lines for boats so they don’t damage reefs when they anchor and tending to a coral nursery where fragments of elkhorn and staghorn corals are growing on underwater ladders. She’s also talking with potential investors about creating a land-based research lab on the island of Providenciales, where endangered and disease-susceptible species could be propagated.

Apart from shipping vessels, scuba gear may also be acting as a disease vector. “I bleach everything,” Zimmermann said. She’s been urging dive shops throughout Turks and Caicos to do the same, although very few do, citing the extra time, money, and water it requires.

Over the course of several reef monitoring dives, Zimmerman pointed out the diversity of life teeming around the corals she’s trying to save. A pair of dolphins played with a piece of sponge coral. A trio of nurse sharks napped in a coral enclave. A hawksbill sea turtle gnawed on an algae-covered coral while a school of hundreds of Horse-eye jack swam nearby.

“If their habitat goes, then they go,” she said.

In January 2020, she received a research permit from the Turks and Caicos government to begin treating designated coral colonies with topical powdered amoxicillin mixed with a paste called CoralCure Ointment Base2b developed by Ocean Alchemists, a company that uses pharmaceutical technologies to make products for the environment.

Later that spring, as Turks and Caicos closed its borders and shut down all on-island activity because of COVID-19, Zimmermann held a series of online Zoom trainings for 70 divers, teaching them how to identify stony coral tissue loss and apply the antibiotic treatment to affected corals. “The day they lifted the local lockdown we were on the water,” Zimmermann said. Almost every diver on the island helped. “It was a golden time for volunteerism.”

Researchers from Nova Southeastern University in Florida found the antibiotic treatment to be 95% effective at stopping the spread of infectious stony coral lesions. Zimmermann has observed similar results.

Still, using antibiotics underwater is controversial. There’s a risk, albeit low, that an antibiotic-resistant form of bacteria could escape into the marine environment, Lang said.

As an alternative, the Turks and Caicos Department of Environment & Coastal Resources is testing the use of a chlorine-based treatment, also trialed in Florida but found to be largely ineffective. Roddy McLeod, an environmental officer with the department, said they’ve modified the original treatment by infusing it into cocoa butter instead of the original epoxy base, with the hope that this will improve the chances of the chemical reaching the affected tissues.

Zimmermann said she’s also begun a trial of a new non-antibiotic treatment created by Ocean Alchemists, although neither would disclose details about it. Until something better comes along, Zimmermann said she’ll continue to use amoxicillin, as well. “We know that it works.”

Forty feet below the water’s surface, Zimmermann hovered horizontally next to a six foot tall pillar coral, or dendrogyra cylindrus, its iconic spires resembling a drip sand castle. Unlike many of its neighboring stony coral colonies, the tan pillar coral was still largely intact, but had begun to show signs of infection at its base.

Zimmermann fluttered her mint-colored fins and maneuvered closer to the ailing coral, aiming her catheter syringe packed with amoxicillin paste and plunging its contents along the white lines of infection, pressing the medication down slightly with her fingers to make sure the mixture stuck.

It’s impossible to treat every coral colony affected by the disease, but over the course of an hour Zimmermann managed to reach eight large pillar, brain, and star corals. Back aboard the boat, still dripping from her dive, Zimmermann sighed and smiled. But before relishing too much over the day’s achievements, she began consulting with the captain about the next best days to dive again.

“We don’t have time to wait,” she said.