In a Stanford University experiment, bleached coral that touched healthy coral recovered within seven weeks, whereas fragments a few millimeters away died of starvation. Physical contact let the corals fuse, giving beneficial algae a route into the bleached tissue within a week.
Published in Science Advances, the findings suggest a way to get recovery started rather than rescue entire reefs. Bleached fragments have to be paired with healthy coral that’s genetically identical, which limits how soon the method can be used on wild reefs.
Corals bleach after they release tiny symbiotic algae known as zooxanthellae. Living inside coral tissue, the algae supply much of the coral’s food; without them, the coral becomes white. That doesn’t mean it’s dead, but it does leave the coral more vulnerable to disease and at risk of starving.
In a university statement on the work, Stanford PhD student Danny Collins said: “While bleached corals may be dying, they are not dead yet.” He added: “The question we wanted to answer is, once a coral has bleached, what can we do?”
The research began with a lucky accident in the lab. According to Euronews, Steve Palumbi, a marine biologist and Stanford professor, observed in 2025 that a coral piece described as dead was getting its color back as it rested against healthy coral.
To distinguish the effects of touching from simply being nearby, the researchers used ten fragments containing bleached pieces. They placed half in contact with healthy fragments and left a gap of just a few millimeters for the others. The touching group recovered and survived, while the fragments kept apart starved.
Looking at the samples through a microscope, Palumbi and his colleagues saw that contact had effectively joined the corals together, letting beneficial algae pass into the bleached pieces. In the statement, Palumbi said the algae “flood in and start dividing at the fastest rates seen in corals,” at approximately ten times their rate in nature.
Stanford professor Fiorenza Micheli, a coauthor of the study, said: “Bleached corals are often considered a lost cause because recovery after a heatwave is very slow, if it happens at all.”
Climate change has driven bleaching worldwide, and events keep getting more severe as temperatures rise. A United Nations Environment Programme report puts the loss of the world’s reefs over the last 30 years at almost ten percent. Helping corals recover after bleaching could protect some reefs, but it’s unclear whether the lab method will work at a larger scale.
It also won’t protect reefs from rising ocean temperatures in the long run. Palumbi told Euronews: “This is a recovery story.” He explained: “It doesn’t blunt heatwaves; it just helps the aftermath. There is still a huge need to reduce heatwaves and protect all of Earth’s life from rapid climate stress.”
Palumbi points to a narrower use: helping “coral gardens survive heatwaves more completely.” Outside the lab, researchers would still need to find a healthy clone to match each bleached coral.
