Bleached Coral Recovers Fast When It Touches a Genetic Clone

Keypoints:

• Stanford University researchers found bleached coral can recover quickly when touching a genetically identical healthy fragment
• Algae begin moving between fragments within 36 hours
• Bleached fragments in the experiment recovered in about seven weeks
• A gap of a few millimetres stopped the recovery
• The method needs a healthy clone for each bleached coral, so it does not yet scale to reefs

Scientists at Stanford University report a surprising shortcut for healing bleached coral. Corals bleach when warm water makes them expel the algae that live in their tissues. Without those partners, they turn pale, starve and become vulnerable to harmful algae. Bleaching is often lethal and threatens reefs worldwide.

The idea started with an accident. In 2025, marine biologist Stephen Palumbi noticed that two coral fragments from one colony had tipped over in a tank and were touching. One was bleached and one was healthy. Palumbi's colleague Danny Collins, a graduate student, then built a controlled experiment around it.

Collins assembled 10 pairs of fragments from the same animal, each pair with one bleached piece and one healthy piece. When the pieces touched, their tissues fused. Genetically identical corals recognize each other, Palumbi explained. He compared it to organ transplants, which work best between identical twins.

Algae and nutrients then flowed through the fused tissue. The transfer began in as little as 36 hours. Recovery was kick-started within about three days, and color returned where the pieces touched. Bleached fragments in contact with a clone recovered in about seven weeks.

The researchers found that the algae replicating inside the bleached fragment drove continued recovery. They did not mainly keep traveling from the healthy partner. A gap of just a few millimetres prevented recovery.

The limits are significant. The method requires contact between genetically identical corals. A healthy clone is needed for every bleached coral, which is not feasible at reef scale. Collins is now exploring ways to deliver concentrated packets of healthy algae without needing identical donors. The team plans to test alternatives that do not need continuous contact.