Corals may have found an unlikely ally in the fight against climate change: bacteria.
During a natural marine heatwave in the Red Sea, scientists discovered that specially selected probiotics—and even treatments made from dead or inactive microbes—could improve the health of heat-stressed corals. The results, published September 3 in Cell Reports, could open a new path for protecting reefs as warming oceans push corals toward their limits.
Coral reefs are among Earth’s most important ecosystems, supporting at least a quarter of marine life. But when seawater stays unusually hot, corals can expel the microscopic algae that help feed them, turning ghostly white in a phenomenon known as bleaching. Severe or prolonged bleaching can be fatal.
Researchers wanted to know whether microbial therapy could help corals withstand that heat outside the laboratory.
Their test came during a 2022 summer heatwave in the central Red Sea, where daily average seawater temperatures reached 87.6°F to 89.5°F (30.9°C to 31.9°C).
The team treated Acropora cf. valida corals with probiotic mixtures containing beneficial bacteria isolated from healthy Red Sea corals. They also tested postbiotics—formulations made from inactivated microbes or their biologically active components.
After 15 days, one probiotic treatment and one postbiotic treatment had significantly improved coral health. Researchers assessed the corals by tracking their color and the photosynthetic efficiency of the algae living inside them.
The postbiotic results were particularly intriguing. Genetic and metabolic analyses showed that the treatment changed the corals’ microbial and chemical profiles, including an increase in Cobetia, a bacterial group associated with heat tolerance.
Postbiotics could also be easier to deploy than live bacteria because inactive formulations may offer longer shelf life, simpler storage and transportation, and lower production costs.
Scientists caution that more research is needed to understand exactly why the treatments work—and whether they can be scaled safely.
Still, the message is encouraging: saving coral reefs may someday involve not only protecting the ocean from heat, but helping corals recruit their own microscopic survival squad.
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