Studies Offer More Hope for Combatting Coral Disease

Diver Matt Davies treats a large brain coral against Stony Coral Tissue Loss Disease at Llews Reef on St. Croix. (Photo by Erin Bowman, courtesy Courtney Tierney)

In the ongoing battle against a devasting coral disease, there may be a new weapon.

Laboratory studies involving a probiotic have shown it to be highly effective in combatting Stony Coral Tissue Loss Disease.

A report published April 6 in “Communications Biology” says the trials showed that Pseudoalteromonas sp. strain McH1-7 slowed the progression of the disease in 68.2 percent of the infected corals, “and it prevented disease transmission by 100 percent.”

SCTLD was first identified in reefs off the coast of Florida in 2014. It affects at least 24 different species of coral, killing it relatively rapidly and spreading easily and quickly, giving it the potential to drastically alter the marine environment.

By the end of January 2019, it had reached the Virgin Islands, where it was spotted by a University of the Virgin Islands professor, Marilyn Brandt, by Flat Key, on the west end of St. Thomas. Within a year, it was found in waters off both St. John and St. Croix.

As of November 2022, according to the report, signs of SCTLD had been discovered in 26 different Caribbean countries and territories.

In the Virgin Islands, joint public-private efforts led by the V.I. Department of Planning and Natural Resources and UVI began immediately and have since mitigated the disease’s impact in territorial waters. Research on various aspects of the disease and its prevention are ongoing, both locally and nationally.

The V.I. Coral Disease Advisory Committee, a group of stakeholders including marine ecology non-profit groups, UVI, DPNR, and the National Oceanic and Atmospheric Administration, was founded in 2020 and remains active.

So far, the most effective approach to containing SCTLD has been the application of an antibiotic substance to diseased coral.

In Florida, amoxicillin, an antibiotic commonly used in both human and veterinarian medicine, has been used to treat more than 22,000 coral colonies, according to the report, with a success rate of between 67 percent and 90 percent, depending on the type of coral.

Results in the territory have been similar.

Courtney Tierney, coordinator of the Coral Disease Response and Restoration program at DPNR, told the Source this week that antibiotic treatment has been successful in roughly 90 percent of the corals where it was applied.

But much damage was done.

“There’s lots of coral that died in that first year,” Tierney said. There was a “huge loss.”

Courtney Tierney and Nicholas Durgadeen, working under Ceiba Strategies, examine a reef in the St. Thomas East End Reserves for signs of Stony Coral Tissue Loss Disease. (Photo courtesy Courtney Tierney)

Volunteer divers were an important part of the initial response to the disease and non-profits remain active in the fight, but government efforts, some federally funded, now rely largely on professional divers contracted for the work, Tierney said, adding that more than 50 divers have been trained for the project.

There are five “strike teams” — some with two members, some with four — that make regular dives in designated areas, she said. To date, they have logged some 900 dives and treated 21,000 corals.

The authors of the study on McH 1-7 suggest that the probiotic may be a good alternative to an antibiotic. In some cases, an antibiotic may have to be reapplied, either because it didn’t work the first time or because the coral is reinfected. Moreover, there are always concerns about the overuse of an antibiotic leading to the development of resistance to it.

While she recognizes the concern over developing resistance, Tierney said it is too early to embrace the probiotics approach, given that it has been tested only in lab studies. Until there are field studies — or ocean studies in this case — there is uncertainty how it will perform on actual reefs and what side effects it may have.

“We’re keeping an eye on that,” she said, referencing research on probiotics. In fact, she said, UVI had done some work on probiotics and SCTLD but it is “on the back burner” right now.

Attempts to reach Brandt for details on the UVI studies were not immediately successful. She was at a SEAS Islands Alliance conference in Guam this week.

Noting that amoxicillin is widely used, Tierney said “any diversity” of treatments might be useful, including a probiotic, once fully proven. “We’re open to adding this into our treatment program.”

With the current success at immediate control efforts of SCTLD and recognition that the disease is not the only thing stressing coral, Tierney said, “We’re shifting from disease response to disturbance response” in the work to protect reefs.

Under consideration are a number of things that have been tried elsewhere, such as removing snails that feed on coral or algae that adversely affects it, she said. Meanwhile, the effort is also turning proactive. Divers retrieve coral specimens that have proven resistant to SCTLD in order to nurture them and then replant them to encourage the development of resistant species.

That doesn’t mean that the SCTLD program is ending.

“We are still having those strike teams out in the water,” Tierney said. “We are always on the lookout” for signs of the disease.

While the outbreak of Stony Coral Tissue Loss Disease hit the three islands at different times, “It’s all pretty evenly spread out throughout the territory,” she said. About 15 to 20 different species found in V.I. waters have been affected by Stony Coral Tissue Loss Disease.

“All the species are affected differently,” she added. Locally, pillar, maze and star corals have been some of the hardest hit.