The controversial idea to save corals is to replace them with new species

Corals are being hit so hard by global warming that the only way to save reef ecosystems may be to replace native species with more heat-resistant ones from other parts of the world. This is the view of two coral researchers who call for the benefits and risks of the deliberate introduction of foreign corals to be carefully assessed, rather than dismissed out of hand.

Living corals are vital to the health of reefs and the people who depend on them, he says Michael Webster at New York University. “Coral does a lot more than just look pretty on the reef. It provides spaces for different organisms to live. It blocks the waves from the coasts, it makes sand for tropical beaches.”

But corals cannot cope with temperatures outside the usual ranges in their place. As sea temperatures rise due to global warming, widespread bleaching is occurring. This is when the corals expel the algal symbionts that provide many of their nutrients, which can ultimately lead to death.

“A lot of places around the world are rapidly losing their coral, and they’ve had mixed results trying to bring it back with more conventional tools,” says Webster.

In an opinion piece written with Daniel Schindler at the University of Seattle, Washington, Webster calls for change. “You may be able to find corals in a very different place that are already adapted to the conditions that arrive in a place, or that could be in that place in the future. You can essentially try to find corals that are pre-adapted,” he says . Many of those who try to save coral reefs are frightened by this idea, but the situation is so bad that we need to seriously consider it, says Webster.

For example, the two species of branching coral native to the Caribbean are in very bad shape, he says. But there are more than 100 species of branching corals in the world, some of which could recreate the habitat provided by branching corals if introduced to the Caribbean. “They won’t necessarily be the same color or anything like that,” says Webster. “But they are similar, ecologically.”

Webster and Schindler admit there are dangers. The worst case scenario is that devastating diseases or predators are accidentally introduced with the exotic corals. Introduced corals may even outcompete native species or hybridize with them.

But there’s also the risk of waiting too long before doing something, says Webster. He thinks that replacing the lost species with those that perform a similar role, which is known as ecological replacement, is much more practical than some other options that are being explored, such as trying to genetically engineer corals to tolerate greater heat. “Our best bet for coral reefs is the existing diversity that is there,” he says.

Terry Hughes at James Cook University in Queensland, Australia, disagrees. “The benign term ‘ecological substitute’ is naive, dangerous and surprisingly arrogant,” he says. “The authors fail to recognize that enormous ecological damage has already been inflicted on the world’s coral reefs by accidental and deliberate introductions of exotic species.”

For example, in the 1980s, an unknown Pacific disease spread from the entrance to the Panama Canal, wiping out algae-eating urchins in the Caribbean, leading to rampant algae growth that killed millions of corals, says Hughes. “Invasive species are a problem for coral reefs, and not a healthy solution.”