Bleached Coral Recovers After Simply Touching a Healthy Coral
In lab experiments, white, near-death corals regained their colour within seven weeks after only a few days of contact with a healthy copy of themselves.
Corals that have turned white and are close to dying can recover simply by touching a healthy coral. In laboratory experiments, badly bleached corals regained their colour and their full health within seven weeks after only a few days of contact with a healthy copy of themselves.
An accident in an aquarium
The idea came from something that happened by chance in 2025. In the laboratory of Steve Palumbi, a professor of marine sciences at the Stanford Doerr School of Sustainability, two fragments taken from the same coral colony — one healthy, one bleached — fell against each other in a tank. Where the two pieces touched, the white coral began to regain its colour.
Around the same time, Danny Collins, an oceans PhD student and the lead author of the study, was investigating how coral diseases develop and spread. He was looking in particular at harmful bacteria that arrive on pieces of plastic and enter corals through direct contact. That gave him a different question: if contact can let harmful things in, could it also let something helpful in? The results appeared on October 14 in the journal Science Advances.
Ten pairs, and a gap of a few millimetres
To test the idea, Collins set up ten pairs of coral fragments. Each pair contained one healthy piece and one bleached piece, and both pieces came from the same coral animal, which made them genetically identical.
Five of the pairs were positioned so that the two fragments physically touched. The other five were held apart by gaps measuring only a few millimetres. The difference between the two groups was stark: every bleached fragment that touched its healthy partner recovered completely within seven weeks, while every bleached fragment kept apart died.
Why the touch works
Corals are animals, not plants or rocks. In most coral species, individual animals reproduce by creating genetically identical copies of themselves, and those copies grow together into the large colonies that form reefs. When two of these identical corals meet, their tissues recognise one another and can fuse. Palumbi compared it to organ transplants in people, which are often successful when the donor is an identical twin.
Looking through a powerful microscope, the researchers saw tiny channels inside the tissues of the two fragments line up and join, forming connections that allowed material to move between them. Beneficial algae — the microscopic organisms that live inside coral tissue and supply much of the energy corals need — passed from the healthy fragment into the bleached one. Algae were seen moving across within just three days.
The team then tested how long the corals actually needed to stay connected. A single week of contact was enough to pass the algae required for a complete recovery, and in some cases five days was enough. Corals separated after that short contact still returned to full health within seven weeks, exactly the same time as corals that stayed joined for the whole experiment. The researchers describe the result as the fastest documented recovery from coral bleaching.
What it could mean for reefs
Bleaching happens when rising ocean temperatures cause corals to lose the algae living inside their tissues. Without those algae, corals lose their colours, struggle to get enough food, and become more open to harmful algae. Even when a bleached coral survives, getting healthy again can take months or years.
A separate study, published in Nature Communications, used a computer model of Australia's Great Barrier Reef to simulate what may happen to 3,800 reefs under current climate projections. It projected a rapid coral decline by the middle of this century under all the emission scenarios the authors tested. It also found that recovery remains possible this century if warming stays below 2 degrees Celsius, and concluded that curbing global warming by 2050 is crucial for corals to keep going.
The touching experiments were done in tanks, not on a reef. They point to a possible tool for restoring damaged reefs, but they do not solve the heat problem described in the modelling work. As the researchers put it, bleached corals may be dying, but they are not dead yet.