The COVID-19 pandemic continues to dominate the news as it takes its toll on human life. Now, some marine biologists in Florida and the Caribbean are also concerned about another epidemic – one that’s raging under the sea.
It’s called Stony Coral Tissue Loss Disease, and its victims – hard corals that make up the structure of coral reefs – are dying at a rate far beyond the death rate exacted by the novel coronavirus. The disease was first spotted on reefs around St. Thomas in January 2019.
On some reefs, the mortality rate of stony corals is as high as 60 percent, according to Joe Townsend, the USVI’s coral disease response coordinator. Fortunately, he said, the disease has not yet been detected on St. Croix.
Frank Cummings, who has gained local fame by leading the fight against invasive lionfish in the Virgin Islands with C.O.R.E., now heads up the St. John Strike Force team, one of three throughout the territory that is scrambling to halt the spread of the disease.
“I’m very anxious; it’s like trying to fight a forest fire with a garden hose,” said Cummings.
Cummings has good reason to be alarmed. The coral disease was first sighted at Frank Bay and Lind Point on the western tip of St. John in January of this year. Since then, it has spread along the northern shore of St. John throughout the Virgin Islands National Park; for reasons unknown, however, not every place along the shoreline has been affected.
Cummings and the St. John team have been conducting roving diver surveys to determine just how widespread the disease is.
The news is not good. Stony Coral Tissue Loss Disease – SCTLD (pronounced like “Skittled”) – as scientists now call it – has been found on reefs near Flanagan and LeDuck, two small cays off the east end of St. John.
New reports of the disease keep coming in. On June 15, one Virgin Islands National Park diver spotted an early stage outbreak at Tektite in Great Lameshur Bay and a severe outbreak at Booby Rock of Salt Pond Bay – both of which are on the south side of St. John.
Like most epidemics, the disease does not respect international boundaries. SCTLD has been identified at the Indians, a popular dive spot near St. John in the British Virgin Islands, and at other sites in the BVI. Shannon Dore of the Association of Reef Keepers (ARK) in the BVI is collaborating with the USVI Strike teams, according to Townsend.
SCTLD was first identified in Florida in 2014 and was found in reefs near Puerto Rico in November 2019, according to Marilyn Brandt, a marine biologist based at the University of the Virgin Islands.
When Brandt first saw it in January 2019 at a dive site known as Flat Cay on the south side of St. Thomas, she said, “My stomach dropped. I’ve been studying coral disease for most of my career. I was shocked by the number of corals affected.”
It wasn’t just the number of coral colonies that were affected, but also the types of species which caused alarm. SCTLD affects about 18 species of coral and is particularly prevalent among brain corals, star corals and others that form the boulder-like structures that make up healthy reefs. “It’s like losing the trees in the rainforest; they’re incredibly important to communities of marine creatures,” said Brandt.
The disease is marked by areas that are stark white, and one of the first tasks of Strike team divers is to learn to distinguish it from other coral diseases, and common “bleaching.” Bleaching occurs when corals shed the symbiotic algae which give corals their color. Bleaching events are often seasonal and result from rising water temperatures and other environmental stressors. Corals can recover from bleaching if the stressor is removed within a few weeks, but SCTLD is almost immediately lethal. For a full explanation, see the Strike Force’s website.
Scientists have found some methods of combating SCTLD – with amputation and with the application of antibiotics – but the work is demanding and labor-intensive. In some cases, qualified Strike team members cut out the portion of a coral that is affected.
They also use a tool like a caulking gun to apply the antibiotic amoxicillin along the margins of the diseased areas. The amoxicillin is mixed in with a sticky base that adheres to corals for several weeks, and with repeated treatment and luck, the disease doesn’t spread beyond the treated area. “Treatment like this is like a firebreak,” Cummings said.
Cummings said he is not without hope; in Florida, the success rate in some treated areas has been as high as 90 percent.
However, it’s unclear that the disease affecting stony corals reefs in the Virgin Islands is identical to the disease in Florida or elsewhere. Microbial ecologist Amy Apprill, of the Woods Hole Oceanographic Institution, is now working with graduate student Cynthia Becker to analyze specific bacterial communities that could be the cause of the disease.
Before the outbreak of COVID-19, Apprill and Becker traveled to St. Thomas to gather samples from corals and surrounding waters.
Because the marine lab at the University of the Virgin Islands was still undergoing repairs caused by Hurricane Irma, they rented a villa through Airbnb and set up a makeshift lab.
They arrived on St. Thomas with mini-centrifuges and a DNA sequencer which allowed them to get results within 18 hours. In two weeks, they were able to get the data for 100 samples and return to their lab at the Woods Hole Oceanographic Institution, just weeks before activities were shut down because of COVID-19.
Now they’re busy analyzing the data from the Virgin Islands, seeking to determine if it matches SCTLD found in other locations. The results should be in soon, according to Townsend.
Brandt and Apprill, along with renowned sea explorer and conservationist Sylvia Earle, discussed their work in a webinar on SCTLD hosted by the Woods Hole Oceanographic Institution that can be seen here.
According to a slide of a map presented during the webinar, outbreaks of the disease continue to pop up throughout the Caribbean.
Although no one knows what’s causing the disease, one theory is that it is spread by a pathogen in the ballast of large sea-going vessels, according to Townsend.
While the cause remains unknown, the fight against SCTLD is ramping up. Cummings said he’s hoping to enlist the help of local divers as he did in the battle to eradicate invasive lionfish. As part of that effort, more than 300 divers have volunteered since the first lionfish was spotted in the Virgin Islands more than ten years ago.
To fight SCTLD, divers need to be able to identify and record multiple species of corals, many of which look similar. The most advanced disease-fighters also need to develop the skills required to amputate diseased coral and apply antibiotics.
However, crowdsourcing by amateurs is valuable. Anyone spotting the “blinding white” signs of the disease is welcome to report their observations on this website. “We’re hoping to keep the curve flattened, to use the COVID-19 metaphor,” said Cummings.