Probiotic Treatment Slows Deadly Coral Disease Threatening Caribbean Reefs.

Researchers at the Smithsonian’s National Museum of Natural History have uncovered a bacterial probiotic that can slow the progression of stony coral tissue loss disease (SCTLD), a devastating illness sweeping through Caribbean coral reefs. Published recently in Frontiers in Marine Science, their study shows that applying this probiotic treatment over entire coral colonies can help prevent further tissue loss.

This new probiotic approach offers a valuable alternative to antibiotics, which have been the primary treatment but only provide temporary relief and raise concerns about fostering antibiotic-resistant strains of SCTLD.

“The goal with probiotics is to have corals incorporate these beneficial bacteria into their natural microbiomes,” explained Valerie Paul, lead scientist at the Smithsonian Marine Station at Fort Pierce, Florida, and co-author of the study. “Once integrated, the probiotics can offer longer-lasting protection.”

SCTLD first appeared in Florida in 2014 and has since rapidly spread throughout the Caribbean. Unlike many pathogens that target just a few coral species, SCTLD affects over 30 types of stony corals, including brain corals shaped like boulders and pillar-like corals with limb-like structures.

The disease causes coral tissue to peel away, revealing white patches of exposed skeleton. Within weeks to months, entire coral colonies can be destroyed. While scientists have yet to pinpoint the exact cause of SCTLD, it is believed to be linked to harmful bacteria. Currently, the standard treatment involves applying a paste infused with the antibiotic amoxicillin directly to infected areas.

However, antibiotics are not a perfect solution. The amoxicillin paste requires frequent reapplication to combat ongoing infections, which demands considerable time and resources. More critically, repeated antibiotic use increases the risk that the bacteria causing SCTLD will develop resistance to the drugs.

“Antibiotics do not prevent future outbreaks,” Paul said. “The disease can return quickly, even on coral colonies that have already been treated.”

In search of a more sustainable solution, Paul and her colleagues have spent over six years investigating whether probiotics—beneficial microorganisms—can help combat the disease. Similar to humans, corals harbor complex communities of bacteria known as microbiomes. These bacteria, found in coral tissue and the mucus corals secrete, produce antioxidants and vitamins essential for coral health.

The team began by studying the microbiomes of coral species that appear resistant to SCTLD, aiming to isolate probiotics that could strengthen vulnerable corals’ natural defenses. They screened over 200 bacterial strains from these disease-resistant corals.

In 2023, they published research on one promising probiotic, Pseudoalteromonas sp. McH1-7, derived from the great star coral (Montastraea cavernosa). This strain produces multiple antibacterial compounds, making it a strong candidate for fighting the diverse threats posed by SCTLD.

Initial lab tests on live pieces of M. cavernosa showed that McH1-7 reliably inhibited SCTLD spread. Encouraged by these results, the team moved to field trials in 2020 on a shallow reef near Fort Lauderdale. They selected 40 M. cavernosa colonies showing SCTLD symptoms and applied the probiotic in two ways: a paste directly on lesions and a seawater solution covering the entire colony.

To apply the solution, the researchers enclosed each treated coral in weighted plastic bags, creating small “mini-aquariums” that kept the probiotic in close contact with the coral.

Over two and a half years, the team monitored these corals, periodically collecting tissue and mucus samples to track microbiome changes. They found that the probiotic significantly slowed disease progression when applied to whole colonies via the solution and bag method.

Importantly, McH1-7 integrated into the corals’ natural microbial communities without overwhelming them. Conversely, corals treated with the probiotic paste lost more tissue than untreated controls, indicating that direct lesion application was less effective.

While the probiotic shows promise for Florida’s northern reefs, further adjustments are needed to optimize treatment in other areas. Preliminary tests in the Florida Keys have yielded mixed outcomes, likely due to regional differences in SCTLD.

Nevertheless, Paul remains optimistic about probiotics as a vital tool in the fight against SCTLD throughout the Caribbean. “Corals naturally host diverse bacterial communities, so it makes sense that these microbes are key to coral health,” she said. “Our work is focused on identifying which bacteria can help make these microbiomes even more resilient.”

This research is part of the Smithsonian’s Ocean Science Center, which unites marine expertise and collections to deepen understanding of ocean ecosystems and support their conservation.

Source:https://phys.org/news/2025-06-probiotics-deadly-disease-decimating-caribbean.html

This is non-financial/medical advice and made using AI so could be wrong.