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By Alice Klein

Chris Jones

It may be possible to protect coral reefs from the warming oceans by colonising them with heat-resistant algae.

Coral reefs around the world are under threat from climate change, which is driving up ocean temperatures. Australia’s Great Barrier Reef, for example, has just suffered its third mass bleaching event in five years after experiencing the hottest February sea temperatures on record.

When seas become too warm, corals lose the colourful Symbiodiniaceae microalgae that live in their tissues and make food for them. This causes the corals to lose their colour, giving them a bleached appearance, and to gradually starve to death.

Patrick Buerger at CSIRO, Australia’s national science agency, and his colleagues wondered whether they could help corals survive warmer waters by increasing the heat tolerance of their resident algae.

They heated Symbiodiniaceae algae to 31°C in a laboratory for four years to train them to tolerate more heat than they are used to. The algae eventually evolved genetic changes that hinted at greater heat resistance.

The researchers then took coral larvae from the Great Barrier Reef, mixed them with either regular algae or the heat-resistant algae and then heated the mix to 31°C for one week, a temperature known to cause bleaching. The coral with the regular algae quickly bleached, but the coral with the heat-resistant algae remained healthy.

The results are promising, but more research is needed to test whether the heat-resistant algae can also be used to prevent bleaching in adult coral, not just larvae, and to see whether it works for different coral species, says Buerger.

“We’re putting all our efforts into this now in case we need it to have it ready as an intervention in the future,” says Buerger. Tackling climate change is still the most important way to save reefs, but scientists are increasingly looking at artificial ways to protect coral in case we don’t cut greenhouse gas emissions fast enough, he says.

Journal reference: Science Advances, DOI: 10.1126/sciadv.aba2498

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