‘Amazing’: Bleached corals thrive within days when they touch a healthy neighbor

Scientists quickly restored bleached corals in the laboratory by placing them in contact with a healthy fragment, providing hope of reversing widespread coral decline.

Rising sea temperatures put stress on corals, forcing animals to expel the symbiotic algae that live in their tissues and give them their color – a process known as bleaching. Since photosynthetic algae (Symbiodiniaceae) provide corals with most of their nutrients, without them, marine organisms are likely to starve and die.

A team of researchers has just shown that it is possible to completely reverse this whitening process, in just a few days. They reported their findings in Scientific advances October 14¹.

“This incredible new result – that rapid and complete recovery is possible in bleached corals – may inspire solutions that could eventually be scalable,” says Fiorenza Micheli, a marine ecologist at the Center for Ocean Solutions at Stanford University in California and co-author of the study.

The healing touch

In early 2025, marine scientist and study co-author Stephen Palumbi of the Hopkins Marine Station in Pacific Grove, California, was working in the lab and noticed two coral fragments in a tank accidentally touching each other. Where the healthy and bleached fragment met, color had begun to seep into the ghostly branch. “I’d never seen that before,” he recalls.

Danny Collins, who was studying how diseases spread through contact with corals as part of his doctorate at Stanford, set out to determine whether algae could also spread and, if so, how.

He prepared ten pairs of coral fragments from the same animal (Pocillopora damicornis), each pair had one bleached fragment and one healthy fragment. He arranged five pairs so that their fragments touched each other, and five with their fragments separated by a few millimeters. In affected pairs, bleached coral recovered within eight weeks.

“We were blown away when we saw the color of the algae symbionts transfer to the bleached coral, reviving it in a very short time,” says Collins. During the second week, the symbiont population doubled every four days, which is much faster than recovery times observed in other studies of natural coral recovery in the wild.^2,3.

After touching the healthy fragment for a week, a bleached branch could fully recover on its own, even if separated from the healthy branch.

In slightly separated pairs, the bleached fragments died after 20 weeks.

Using high-power microscopy, the team showed that two coral fragments merge creating a tissue bridge, enabling the transfer of symbionts. This only happened for coral fragments taken from an individual of the same genetic makeup, called a genet. Fragments from different species or even different animals of the same species did not merge and therefore did not heal the bleached piece.