Probiotics can help heal ravaged coral reefs

Yahoo

05-06-2025

Probiotics are everywhere, claiming to help us poop, restore gut health, and more. They can also be used to help threatened coral reefs. A bacterial probiotic has helped slow the spread of stony coral tissue loss disease (SCTLD) in wild corals in Florida that were already infected with the disease. The findings are detailed in a study published June 5 in the journal Frontiers in Marine Science and show that applying this new probiotic treatment across coral colines helped prevent further tissue loss.
SCTLD first emerged in Florida in 2014. In the 11 years since, it has rapidly spread throughout the Caribbean. This mysterious ailment has been confirmed in at least 20 other countries and territories.
Other coral pathogens typically target specific species. SCTLD infects more than 30 different species of stony corals, including pillar corals and brain corals. The disease causes the soft tissue in the corals to slough off, leaving behind white patches of exposed skeleton. The disease can devastate an entire coral colony in only a few weeks to months.
The exact cause of SCTLD is still unknown, but it appears to be linked to some kind of harmful bacteria. Currently, the most common treatment for SCTLD is using a paste that contains the antibiotic amoxicillin on diseased corals. However, antibiotics are not a silver bullet. This amoxicillin balm can temporarily halt SCTLD's spread, but it needs to be frequently reapplied to the lesions on the corals. This takes time and resources, while increasing the likelihood that the microbes causing SCTLD might develop resistance to amoxicillin and related antibiotics.
'Antibiotics do not stop future outbreaks,' Valerie Paul, a study co-author and the head scientist at the Smithsonian Marine Station at Fort Pierce, Florida, said in a statement. 'The disease can quickly come back, even on the same coral colonies that have been treated.'
Paul and her colleagues have spent over six years investigating whether beneficial microorganisms (aka probiotics) could be a longer lasting alternative to combat this pathogen.
Just like humans, corals are host to communities known as microbiomes that are bustling with all different types of bacteria. Some of these miniscule organisms produce antioxidants and vitamins that can help keep their coral hosts healthy.
[ Related: Caribbean coral is getting sick and dying. A probiotic could help. ]
First, the team looked at the microbiomes of corals that are impervious to SCTLD to try and harvest probiotics from these disease-resistant species. In theory, these could be used to strengthen the microbiomes of susceptible corals.
They tested over 200 strains of bacteria from disease-resistant corals and published a study in 2023 about the probiotic Pseudoalteromonas sp. McH1-7 (or McH1-7 for short). Taken from the great star coral (Montastraea cavernosa), this probiotic produces several antibacterial compounds. Having such a stacked antibacterial toolbox made McH1-7 an ideal candidate to combat a pathogen like SCTLD.
They initially tested McH1-7 on live pieces of M. cavernosa and found that the probiotic reliably prevented the spread of SCTLD in the lab. After these successful lab tests, the wild ocean called next.
The team conducted several field tests on a shallow reef near Fort Lauderdale, focusing on 40 M. cavernosa colonies that showed signs of SCTLD. Some of the corals in these colonies received a paste containing the probiotic McH1-7 that was applied directly to the disease lesions. They treated the other corals with a solution of seawater containing McH1-7 and covered them using weighted plastic bags. The probiotics were administered inside the bag in order to cover the entire coral colony.
'This created a little mini-aquarium that kept the probiotics around each coral colony,' Paul said.
For two and a half years, they monitored the colonies, taking multiple rounds of tissue and mucus samples to see how the corals' microbiomes were changing over time. They found that the McH1-7 probiotic successfully slowed the spread of SCTLD when it was delivered to the entire colony using the bag and solution method. According to the samples, the probiotic was effective without dominating the corals' natural microbes.
While using this probiotic appears to be an effective treatment for SCTLD among the reefs of northern Florida, additional work is needed to see how it could work in other regions. Similar tests on reefs in the Florida Keys have been conducted, with mixed preliminary results, likely due to regional differences in SCTLD.
The team believes that probiotics still could become a crucial tool for combatting SCTLD across the Caribbean, especially as scientists fine tune how to administer them. Importantly, these beneficial bacteria support what corals already do naturally.
'Corals are naturally rich with bacteria and it's not surprising that the bacterial composition is important for their health,' Paul said. 'We're trying to figure out which bacteria can make these vibrant microbiomes even stronger.'