When the sea becomes too warm, corals experience significant stress. They can lose the tiny algae that live in their tissues and give them much of their color. Without them, corals bleach, weaken, and risk dying.
Researchers at Stanford University in California wanted to know whether a healthy coral could help a bleached neighbor. The idea seems simple: allow the algae present in one coral to pass to the other. It remained to be seen whether such a transfer was possible.
Corals with vivid colors.
Photo: Ryan Goehrung, via Wikimedia Commons.
The team prepared ten pairs of small coral fragments. Each pair consisted of a healthy piece and a bleached piece from the same individual. In five pairs, the fragments touched. In the other five, a few millimeters separated them.
The difference was spectacular. The five bleached fragments placed in contact with their healthy neighbor recovered within seven weeks. Those that remained separated did not regain their algae and eventually died during the experiment.
To understand what was happening, the researchers observed the corals under a microscope. When two genetically identical pieces touch, their tissues can fuse and create continuity between them. The helpful algae then pass from the healthy fragment to the bleached fragment, where they begin to multiply.
The contact does not even need to last seven weeks. In some trials, a few days were enough to transfer algae, and one week of contact allowed the bleached fragments to continue recovering on their own. The algae that settled in then multiplied rapidly.
There is, however, one important condition: the fragments must come from the same coral or be genetically identical. Different corals generally do not fuse in this way.
These results open up a possible way to help some weakened corals, but the experiment involved only ten pairs of fragments kept in the laboratory. It will be necessary to determine whether this method can work on entire reefs. Above all, it does not eliminate the main cause of bleaching: warming water.