Climate|To Heal These Bleached Corals, All It Took Was a Little Touch

Danny Collins looked into his microscope and could scarcely believe his eyes: A piece of healthy coral was healing a sick one just by touching it.

These were tiny coral nubbins, not a whole colony. And they were in a lab in California, not on an actual reef. Still, the transformation was striking: The ghostly, heat-shocked coral was regaining its color in a matter of weeks, not the months it might take in the wild.

“Wow, not only is this happening,” Mr. Collins, a doctoral student in ocean science at Stanford University, remembers thinking. “It is happening at an incredible rate.”

His and his colleagues’ discoveries, in that experiment and the ones that followed, point to intriguing new possibilities for treating reefs that are devastated by marine heat waves, which are becoming more frequent because of climate change.

When the water around corals becomes too warm, they expel the colorful algae living inside their tissues. These algae use photosynthesis to nourish the corals; the corals provide shelter in return. But when heat stress severs this partnership, the corals starve and grow sickly. Their white limestone skeletons show through.

Bleached corals can recover if the water doesn’t stay hot for long. But repeated bleaching or prolonged exposure can be fatal. By some estimates, coral cover worldwide has shrunk by half since the 1950s, leading to diminished fish habitats, increased exposure of coastlines to storms and immeasurable losses of natural beauty. More catastrophic decline might be upon us soon: In the coming months, the El Niño pattern in the Pacific Ocean is expected to bathe many reefs in record-warm waters.