Coral reefs might look like static structures, but in reality, they’re living systems teeming with life—some of it too small to see. Much like our own gut health depends on a healthy balance of bacteria, corals rely on complex microbiomes to stay resilient. These bacteria live in their tissue and mucus, helping the coral fight off disease and stress. But when that balance is thrown off—by pollution, warming seas or pathogenic invaders—the corals become far more vulnerable. Now, researchers are testing a surprising remedy: probiotics, similar to the kind found in yoghurt.
An underwater crisis
In the past decade, Florida’s coral reefs have been hit hard by a fast-spreading disease called stony coral tissue loss disease (SCTLD). First identified near Miami in 2014, the disease has spread across the Caribbean, with some sites seeing up to 100% mortality in affected coral species. According to NOAA, SCTLD impacts over 20 species of hard coral and can kill colonies in a matter of weeks.
The disease works quickly, eating away the living tissue and leaving behind white, skeletal remains. What’s worse is that we still don’t fully understand what causes it. Researchers suspect a complex cocktail of bacteria, possibly aided by viruses. It spreads through water, touch, and even on diver gear. The most common treatment has been applying an antibiotic paste directly to lesions—but that’s a short-term fix and carries risks, including the rise of antibiotic-resistant bacteria.
A potential breakthrough in bacteria
So, scientists started looking at what made some coral colonies naturally resist SCTLD. A promising clue came from the great star coral, Montastraea cavernosa. One resilient colony hosted a bacterial strain called Pseudoalteromonas sp. McH1‑7, which produces natural antibacterial compounds. In lab trials, this bacterium slowed or even stopped SCTLD progression in coral fragments.
To test its potential in the wild, researchers at the Smithsonian Marine Station designed a two-year field experiment. Coral colonies were either left alone, treated with a paste made from the probiotic, or enclosed in a bag filled with seawater containing McH1‑7. The bagging method, in particular, mimicked a short-term probiotic soak.
The results were encouraging. Corals given the two-hour probiotic bath lost just 7% of their tissue compared to 35% in the untreated control group. Even more promising was the fact that these improvements lasted over the long term. In a paper published in Communications Biology, researchers described how the probiotic integrated into the coral microbiome without wiping out other beneficial microbes. It appeared to work not by taking over, but by fitting in.
Interestingly, the paste approach actually caused more harm. Scientists think the paste may have interfered with gas exchange or irritated the coral. “McH1‑7 is beneficial at specific dosages,” said marine microbiologist Amanda Alker. “Too much may be harmful.” It’s a reminder that delivery matters as much as the probiotic itself.
Learning from the Red Sea
This isn’t the first time scientists have explored the idea of coral probiotics. Research in the Red Sea found that introducing a cocktail of bacterial strains—including Pseudoalteromonas, Bacillus, and Halomonas—could help shape coral microbiomes in useful ways. The work, published in Microbiome, showed that the probiotic mix successfully colonised the coral without affecting the surrounding seawater.
That Red Sea study laid the groundwork, but the Florida trial went a step further by testing the bacteria against a real disease threat. In that sense, it marks a big leap forward—not just theory, but practical field use.
Why probiotics might matter more than ever
Coral reefs are more than just pretty ecosystems. They buffer coastlines from storms, support fisheries, and are home to an estimated 25% of all marine species. And they’re under threat. Between warming oceans, overfishing, pollution and new diseases like SCTLD, the outlook is grim. A recent IPCC report warns that up to 90% of reefs could disappear by 2050 if global temperatures rise beyond 1.5°C.
This is why innovations like microbial therapy feel urgent. Unlike antibiotics or manual cleaning, probiotics offer a potentially long-lasting solution that works with nature rather than against it. They’re less likely to cause unintended consequences like resistance, and could be tailored to suit different coral species or regions.
Of course, bagging individual corals isn’t scalable. But scientists are already thinking bigger. Biodegradable delivery wraps, slow-release gels, and even drone-assisted dosing are being explored. The research team is now studying how the treatment might work in other parts of the Caribbean, where the disease may behave differently.
What comes next?
One key takeaway from the Florida field test is that timing and delivery are everything. The probiotic doesn’t need to dominate; it just needs to support the coral’s natural microbial defences long enough to tip the balance. More studies are already underway, including experiments with multiple bacterial strains, each targeting different threats.
The next challenge will be making these treatments viable on a larger scale. Still, this isn’t just a quirky experiment—it’s a legitimate piece of the broader conservation puzzle. Coral restoration has come a long way, and microbiome engineering might be one of the most exciting frontiers.
For now, it’s clear that saving coral reefs will require creativity, urgency and tools that work in tune with the living systems they aim to protect. Probiotics might sound like an unlikely hero, but if yoghurt bacteria can help humans thrive, it’s not so strange to think they could help coral too.