A bleached coral regained its color after just one week of touching a healthy piece of the same colony, according to a laboratory study published Oct. 14 in Science Advances by researchers at Stanford University. The healthy fragment passed along the tiny algae that corals depend on, jump-starting the bleached coral's recovery.

The finding offers a rare bit of hopeful news after the most widespread coral bleaching on record, which exposed about 84% of the world's reef area to bleaching-level heat stress, according to NOAA figures cited by ABC News. Bleached corals can take months or years to recover naturally, and many die before they do.

There are important limits, and the researchers state them plainly. The experiment used genetically identical fragments in tanks, and the effect disappeared when the corals were from different genetic backgrounds or were not touching.

A Chance Observation in a Lab Tank

The discovery began by accident. Two fragments of the same cauliflower coral colony, Pocillopora damicornis, one bleached and one healthy, had fallen against each other in a tank, and color began returning to the bleached piece where they touched, according to ScienceAlert. Stanford marine scientist Steve Palumbi first noticed the effect.

Lead author Danny Collins, a Stanford doctoral student, then designed experiments to test it. He found that the touching corals fused their tissues, creating a bridge that carried nutrients and symbiotic algae from the healthy coral into the bleached one.

The transfer began quickly. Algal symbionts started moving between fragments as early as 36 hours after contact, ABC News reported. Recovery was just as fast whether the corals stayed together for seven weeks or were separated after one week, suggesting the algae multiplied on their own once they arrived.

Collins described the larger lesson in the ScienceAlert report: "While bleached corals may be dying, they are not dead yet."

A Speed-Up Measured in Weeks, Not Months

Corals bleach when heat stress causes them to expel the algae living in their tissues, which provide most of their food and their color. Without those partners, corals starve slowly. Recovery depends on the algae repopulating, a process that in the wild can take months, during which weakened corals may die from disease or further heat.

In the lab, bleached fragments recovered within about seven weeks after a week of contact. ScienceAlert described this as roughly an order of magnitude faster than recovery in wild bleached populations. That comparison comes from the coverage rather than a matched field control in the experiment, so it should be read as an approximate benchmark.

The gap test was striking. When healthy and bleached fragments were placed just a few millimeters apart without touching, there was essentially no recovery. Physical contact was the key ingredient. That detail also rules out the idea that the healthy coral was simply releasing algae into the water for the bleached fragment to absorb, since corals sitting side by side in the same tank did not recover.

Same-Clone Contact and Other Hurdles

The biggest obstacle is genetics. When the team paired corals from different genetic backgrounds, the fragments reacted against each other, and no recovery occurred, a response Collins compared to a rejected organ transplant. He told ABC News the method "requires contact of corals of the same genetic clone," which makes it unlikely to work across wild reefs.

The study also tested a single species in controlled tanks. Sample sizes were not detailed in the public coverage, and the results have not been tested on reefs, where water flow, predators, disease and repeated heat waves complicate recovery.

Scale is another problem. Bleaching is projected to become more frequent and widespread under continued warming, and hand-pairing coral fragments cannot keep pace with reef-wide events. Collins has said the real goal remains preventing bleaching in the first place.

The researchers suggest a possible next step: extracting algae from healthy corals and delivering them directly to bleached ones, without physical contact. That idea has not yet been tested.

Potential Uses for Nurseries in Florida and Hawaii

The most realistic near-term use may be in coral nurseries. Restoration programs in Florida, Hawaii, and the Caribbean already grow coral fragments from the same parent colonies before transplanting them to reefs. If a nursery fragment bleaches during a heat wave, pairing it with a healthy clone could, in principle, help it bounce back faster. That application is speculative until tested.

Stanford marine ecologist Fiorenza Micheli said in the ScienceAlert coverage that the insights give hope and could help accelerate reef restoration. The public coverage did not include comment from independent coral scientists outside Stanford.

For residents and visitors in reef states, the practical guidance has not changed. Follow NOAA Coral Reef Watch bleaching alerts, respect closures of stressed reef sites, avoid touching coral while snorkeling, and reduce runoff from fertilizers and septic systems that adds stress to reefs. Nature World News recently reported on another reef recovery tool, underwater speakers that drew more baby coral in Hawaii.

The next milestone is field testing. Until that happens, the study is best read as a proof of concept showing bleached corals can rebound quickly under the right conditions. With a strong El Niño building, reef managers will be watching for practical ways to help corals survive the next heat wave.

The takeaway is cautious optimism. A healthy coral can rescue a bleached clone in the lab within weeks, but turning that into a reef-scale tool will require new methods, and cutting the heat stress that causes bleaching remains the core solution.

What Readers Want to Know

What did the coral study find?

A bleached coral recovered after one week of physical contact with a healthy fragment of the same colony, which passed along algae and nutrients through fused tissue.

How fast was the recovery?

Algae began transferring within about 36 hours, and bleached fragments recovered within about seven weeks, far faster than typical natural recovery.

Can this be used to save wild reefs?

Not yet. It worked only between genetically identical corals in direct contact, in a lab, and has not been tested on reefs.

Which coral species was studied?

Pocillopora damicornis, commonly called cauliflower coral.

What happens if corals are not touching?

Fragments placed just a few millimeters apart showed essentially no recovery.

What can I do to help reefs?

Follow reef closures, avoid touching coral, reduce fertilizer and septic runoff, and track NOAA Coral Reef Watch alerts if you live near reefs.