Lab-grown coral clones restore bleached partners in seven weeks

In a laboratory tank, something unexpected happened: a bleached coral, nearly dead and stripped of the algae that keeps it alive, touched a healthy genetic twin and began to recover. Within seven weeks, it was whole again. The fragments that never made contact with their healthy counterparts simply died. This is what researchers discovered in controlled experiments, work that hints at a possible tool for saving reefs as ocean temperatures continue to climb.

Coral bleaching is a straightforward catastrophe. When water gets too warm, corals expel the symbiotic algae living inside their tissues—the same algae that feeds them and gives them color. Without it, a coral turns white, starves, and becomes prey to opportunistic infections. Normally, recovery takes months or years, if it happens at all. The question scientists have been asking is whether there's a way to speed that process up.

The experiment was elegantly simple. Researchers took ten pairs of coral fragments, each pair consisting of one healthy piece and one severely bleached piece, both genetically identical and both originally from the same animal. In five pairs, they let the fragments touch. In the other five, they left a gap of several millimeters between them. The result was stark: every bleached fragment in contact with its healthy clone recovered completely within seven weeks. Every bleached fragment kept separate died. Lead researcher Danny Collins noted that bleached corals exist in a precarious state—they are dying, but not yet dead, which means intervention remains possible.

What happened at the cellular level was equally striking. When the genetically identical fragments touched, their tissues fused. Microscopic examination revealed that channels within the tissue aligned and formed connections, creating pathways for the movement of substances between the two pieces. The symbiotic algae began transferring almost immediately. Within three days of contact, researchers could detect algae moving into the bleached coral. One week of contact was enough for full recovery in most cases; in some instances, five days sufficed. Even after the fragments were separated, the bleached coral continued to heal. The algae that had migrated into it multiplied with remarkable speed—roughly doubling every four days in the second week, a rate about ten times faster than what occurs in wild coral populations.

But the researchers are careful about what this means. The method works in a laboratory with genetically identical pairs, a condition that does not exist in nature at scale. Each bleached coral would need a healthy genetic clone to recover, and producing those clones for thousands or millions of damaged corals is not feasible with current technology. The real-world application remains distant. What the team plans to do next is investigate whether they can introduce beneficial algae into bleached corals without requiring physical fusion—essentially, delivering the cure without needing the donor. That work is still ahead of them, but the laboratory results suggest the biology is willing to cooperate.