Treating Corals With Bacteria Can Help Reefs Endure Severe Heat, Study Shows

Corals that have turned white in a bleaching event.

Corals that have turned white in a bleaching event. Morgan Bennett Smith / KAUST

Recent years have seen a spate of coral bleaching events, where reefs stressed by unusually warm waters turned white. Scientists have sought different ways of protecting corals from such bleaching, such as pumping cold water into threatened reefs or engineering the algae that live in corals to better tolerate heat. In the latest entry into this field, researchers determined that treating corals with friendly bacteria before an ocean heat wave may help them recover from the resulting bleaching event.

When the sea grows too hot, corals expel the colorful algae that live in their tissues, leaving them at greater risk of disease or death. If the waters cool again, corals may heal, but longer and more intense ocean heat waves brought about by climate change will make it harder to do so. To help reefs better cope with rising temperatures, researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia investigated the role that probiotics could play in their recovery.

Scientists treated corals with six beneficial bacterial strains and then subjected them to temperatures as high as 30 degrees C (86 degrees F) in a simulated ocean heat wave. Corals given the probiotic treatment responded the same as the corals given a placebo — both groups bleached. But once temperatures returned to a more manageable 26 degrees C (79 degrees F), the probiotic group made a complete recovery, with 100 percent of corals surviving, compared to just 60 percent in the placebo group. The findings were published in the journal Science Advances.

If greenhouse gas emissions continue unchecked, all the world’s reefs could bleach by the end of this century, according to the UN Environment Programme. Probiotic treatments may help reefs endure these events, but they are no substitute for cutting emissions, researchers said.

“Using a probiotic is an effective tool to help corals deal with the heat stress, but we also have to consider other interventions,” including “decreasing greenhouse gas emissions and trying to change our resource use,” said Erika Santoro, a postdoctoral fellow at KAUST and lead author of the study. “Corals will need all of these interventions.”