A brutal disease is ravaging Florida’s reefs. Stony coral tissue loss disease first cropped up in 2014 in the shallow waters near Miami, before spreading north along the coast as well as south and west into the Keys. Roughly 80 percent of Florida Reef Tract, a system similar to a barrier reef, is now affected. In response, scientists studying the disease are teaming up with institutions and the public in a massive coordinated effort to stem the spread of stony coral tissue loss disease and look ahead to someday restoring the reefs that have already been damaged.
As its name implies, the disease causes the coral’s colorful tissue to slough off a colony, exposing its bright white skeleton, says Erinn Muller, a coral reef ecologist at Mote Marine Laboratory. This is death of coral tissue itself, unlike bleaching, which occurs when coral lose their symbiotic algae. The pathogen’s identity is yet unknown, but about half of Florida’s 40-some coral species are susceptible, with some, such as pillar corals, being completely wiped out in areas hit by the disease.
“When you go to some of these areas where the disease has been prevalent for a few years, it’s like looking at the moon sometimes. You can swim and swim and swim and not see a single living coral,” says Karen Neely, a coral ecologist at Nova Southeastern University.
In response to the epizootic, the animal analog of an epidemic, the Florida Department of Environmental Protection is coordinating 10 teams with members from about 60 institutions. “It’s easy to be discouraged by this disease outbreak. It is unprecedented in nature,” says Muller. “But the response and the mobilization and the community effort . . . is unprecedented as well.”
One step is to figure out what causes stony coral tissue loss disease. Muller and a consortium of scientists are working to pin down the identity of the culprit, which looks to be bacterial, as antibiotics can thwart the disease. Some of the disease detectives are working with culture-based methods to try to grow the bug, while Muller’s work centers on sampling and sequencing the microbiome of affected corals. So far, Muller and collaborators have detected a couple of types of bacteria, sometimes found in healthy corals at lower abundances, that dominate sick corals’ microbial communities. The team has also grabbed DNA from waters near diseased corals and noticed increased numbers of the suspect microbes they’ve identified.
Meanwhile, others are working to fight the disease’s spread on the reef. One approach is to use a chlorinated epoxy resin that forms a physical barrier to isolate the affected area while the chlorine kills the microbes. Neely’s team smothers diseased patches on corals in the Keys with the treatment, then slices through the tissue using an underwater angle grinder about five centimeters away from the diseased part of the reef to create a “firebreak” that keeps the disease from spreading any further. She describes the technique as somewhat “medieval,” akin to amputation or sticking leeches on people. “But it is what we have right now,” she says.
Researchers have also been experimenting with antibiotics. In the lab, Neely and her colleagues have seen the disease knocked out when tanks are dosed with amoxicillin, for example. But dosing the reef can’t be done in open water. Instead, a Florida-based pharmaceutical manufacturing company has designed a gel to deliver the drug to afflicted corals.
With the help of FORCE BLUE, a group of elite combat veterans, Neely’s team has treated some 600 to 700 corals with either the chlorinated epoxy plus firebreak or the antibiotic gel. Preliminary results show that the two treatment types, used separately, are each around 50 to 60 percent effective. “The fact that we’re making an impact is undeniable,” says Neely. “These treatments are saving corals that would otherwise be dead.”
In addition to applying these treatments to affected reefs near Miami, ecologist Brian Walker of Nova Southeastern University and his collaborators are collecting the spawn of corals that have survived the disease to help propagate a new generation for restoration. Corals spawn once a year. To catch them in the act, Walker and colleagues go out to the reef at night and wait underwater until corals release their bundles of eggs and sperm, which they collect with a net and mix in a bucket to allow fertilized gametes to form. From these, the researchers can lab-rear corals to plant back on the reef someday. “It’s a huge amount of effort for a small amount of coral, relatively speaking,” says Walker. “But it’s a start to save their genetic diversity before perhaps this disease continues its course.”
Yet another effort to preserve the genetic diversity of Florida’s reefs is racing to stay ahead of the disease. The Coral Rescue Project is pulling coral colonies off of the reef in areas the disease hasn’t yet touched. So far they have collected 250 coral specimens, but they are working toward a total of 4,200, or 200 each of 21 susceptible species, by the end of this year. These corals will serve as a genetic bank for captive breeding, with baby corals living in aquaria or labs for 5 to 10 years until they can be planted back on the reef, says Rob Ruzicka, a coral reef ecologist at the Florida Fish and Wildlife Conservation Commission who is part of the project. “Nothing like this has ever been done anywhere in the world.”
It has been a logistical challenge to raise funding and find partners to house and care for corals for such a long period of time, but scientists have pushed forward because, for now, many see it as the only option to save the reef’s biodiversity. Stony coral tissue loss disease is attacking many large framework-building corals, including some that are hundreds of years old. These reef architects can’t be replaced quickly, and their loss will change the reef and alter the populations of fish, crustaceans, and other creatures who call it home. “The reef will be fundamentally different after this event for some time to come,” Ruzicka says. He and others hope that banking the corals to plant later could jumpstart the reef’s future restoration.
If there’s any good news, it’s that Florida’s branching corals, which were hit hard by white band disease in the 1970s, don’t seem to be susceptible. And scientists, including Muller and her crew at Mote, are working on putting tens of thousands of aquarium-raised branching corals back onto the reef.
But the new epizootic seems to be reaching past Florida and its devastation may yet extend to other parts of the Caribbean. So far there’s evidence of its spread to the Virgin Islands, Jamaica, Mexico, the Caymans, and other islands. As such, the prognosis is not good. “I’ve told all my friends to go visit your favorite reef in the Caribbean because it may not be there in five years,” says Walker. “We were at ground zero essentially, and we’ve seen the reef change. It’s changed for at least my lifetime and probably my kids’ too because it takes so long for . . . the system to recover.”
Yet, researchers are hopeful that the ongoing efforts to fight the disease and prepare for future restoration once the epizootic is under control will, eventually, pay off. “If there’s any upside to what we’re seeing here, it’s that it has brought scientists and funders and institutions together in a way that I have never ever seen within the coral community,” says Neely. “I think everyone realizes that if we don’t address this problem, we [won’t] have problems to talk about in the future. There will be no coral left for us to study.”