15 OCT 2026 — Bleached corals that are close to death can make a full recovery in about seven weeks if they are briefly touched by a healthy piece of the same coral, a laboratory study from Stanford University has found. The healthy fragment passes over the algae that corals depend on, through tissue that fuses where the two meet. Within days, the algae in the bleached coral start multiplying faster than recovering corals usually manage in the wild.
The researchers are careful about what the study does not show. It worked only between corals of the same genetic line, and only with small fragments in tanks, not on a reef.
Why bleaching kills
Reef-building corals depend on microscopic algae inside their tissues for most of their food and their colour. When the water gets too warm, the corals expel the algae. The coral turns white, starts to starve and becomes vulnerable to harmful algae moving in. Recovery, when it happens at all, usually takes months to years, and many bleached corals die first.
"While bleached corals may be dying, they are not dead yet," said lead author Danny Collins, a PhD student at the Stanford Doerr School of Sustainability, in the university's announcement. "The question we wanted to answer is, once a coral has bleached, what can we do?"
An accident in the lab
It started with an accident. In 2025, senior author Steve Palumbi noticed that two fragments from the same coral colony, one bleached and one healthy, had tipped over in a tank and were touching. Where they touched, colour was returning to the bleached piece.
Collins then set up a simple test with ten pairs of fragments taken from the same animal, using cauliflower coral (Pocillopora damicornis), the species named in the paper. Five pairs were placed so the fragments touched; the other five sat a few millimetres apart. The bleached corals that touched a healthy partner recovered within seven weeks, while those left separate died. The team says this is the fastest recovery of a bleached coral yet documented.
How the rescue works
Under the microscope, the tissues of the two fragments fused and tiny channels lined up, creating a path between them. Healthy algae and the nutrients they produce flowed across within three days. Brief contact was enough. The paper in Science Advances reports that one week of contact, sometimes as little as three days, supplied enough algae for the bleached coral to finish recovering after the pair was separated.
Most of the recovery came from algae multiplying inside the bleached coral, not from a steady stream from the donor. By one week, the algae population was doubling about every four days, up to ten times faster than most recovery rates seen in corals in the field. "They flood in and start dividing at the fastest rates seen in corals," Palumbi said.
The catch, and the next step
The fusion only happens between corals of the same genet, meaning clones descended from one original coral. Pairs from different genetic lines treated each other as enemies: within hours they extended filaments lined with stinging cells, the paper reports. Palumbi compares the rule to human medicine: "Organ transplants are often successful if the donor is your identical twin." The study did find a second, slower route: polyps can take up algae on contact even between unrelated corals, but that alone was not enough to save a colony.
From the tank to the reef
Collins does not expect reef managers to press corals together one by one. "We likely will not be touching corals to each other on reefs," he told AFP, since the method needs a genetically identical healthy copy of every bleached coral. The team now plans to look at collecting algae from healthy corals well before a heatwave and delivering them to bleached corals in large batches, the university says. That would avoid the genetic mismatch, since the problem lies with the corals, not the algae. For reefs facing a hot El Nino year, that is an early lead, not a fix, but it does change bleached corals from lost cause to possible rescue.
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