Ghostly white corals brought back to full health in 7 weeks in Stanford breakthrough

Stanford: Coral bleaching, one of the most visible impacts of climate change, has been reversed at record speed using a surprisingly simple method developed at Stanford University.

Corals that were ghostly white returned to full health in just seven weeks in the lab – the fastest documented recovery to date, and the first time scientists have seen bleached corals on the brink of death fully recover through brief contact with healthy clones.

The breakthrough, published in the journal Science Advances, opens new possibilities for restoring reefs damaged by warming oceans.

Coral reefs, which protect coastlines from storms and flooding, expel the beneficial algae living in their tissues when ocean waters warm. The loss leaves them pale, starving and vulnerable to harmful algae invasion.

But as lead author Danny Collins, a PhD student at Stanford’s Doerr School of Sustainability, says: while bleached corals may be dying, “they are not dead yet.”The discovery was almost accidental. In 2025, co-author Professor Steve Palumbi observed two coral fragments – one bleached, one healthy – sampled from the same colony that had tipped over and were touching in a lab tank. Where they made contact, color returned to the bleached fragment.

Around the same time, Collins was studying how harmful bacteria from plastic debris enters corals through physical contact.”Harmful bacteria enter corals through physical contact, (so) we were curious about what would happen if we used contact to reintroduce something good – the beneficial algae from healthy corals,” Collins explained.

He arranged five pairs close enough to touch, leaving gaps of just a few millimeters between other pairs. The bleached fragments in touching pairs fully recovered within seven weeks, while those without contact died.

“Genetically identical corals recognize one another when they come into contact, and their tissues fuse,” said Prof. Palumbi. “We see something similar in humans. Organ transplants are often successful if the donor is your identical twin.”Microscopic channels in the coral tissues align shortly after contact, creating a pathway for algae and nutrients to flow from the healthy coral to its bleached counterpart, kickstarting recovery in as little as three days.

The team also found that continuous contact wasn’t necessary. After just five to seven days of touching, bleached fragments had received enough beneficial algae to complete recovery on their own after separation.

Once inside, the algae didn’t just spread – they exploded in numbers. During the second week of contact, algae within bleached fragments doubled every four days, about ten times quicker than the rate observed in wild corals.”Once beneficial algae enter bleached corals, they don’t just spread out. They flood in and start dividing at the fastest rates seen in corals,” Palumbi said.

For years, bleached corals have often been considered a lost cause, while researchers explored solutions like selectively breeding heat-tolerant corals, cultivating coral nurseries and transplanting microbiomes.

The Stanford team now plans to explore alternative ways of delivering beneficial algae that don’t require continuous contact.”These new insights into how corals can naturally recover give us hope for the future,” said Prof. Fiorenza Micheli. “They open the door to what’s possible and may lead to the breakthrough we need to accelerate reef restoration.”