7.5 percent of the reefs are believed to be home to heat-resistant corals. And that offers hope for the future.

Last week, Australian authorities released some rather worrying news. Once again, a huge amount of coral in the vast Great Barrier Reef is bleaching. It is the fourth time in just six years that the reef has been hit hard by bleaching. And so scientists are not unduly concerned. One new study offers a glimmer of hope, however. Because it is possible that the heavily infested reef also harbors quite a lot of unruly corals, which can hold their own despite the high ocean temperature.

bleaching waves

As mentioned, the corals on the Great Barrier Reef have been hit hard by bleaching several times in recent years. In 2016, scientists watched with dismay how record-breaking coral in the world’s largest coral reef was dying. In 2017, the Great Barrier Reef then had to endure it again. The reef was barely out of this period of massive bleaching before the next wave arrived in 2020. And now the reef is again taking heavy blows.

La Nina

The cause is not complicated. It all has to do with rising water temperatures as a result of global warming. However, what makes the current bleaching wave particularly concerning is that it is happening despite last year’s La Niña. La Niña is actually the opposite of the well-known El Niño and thus has a temporary global cooling effect. But the Great Barrier Reef apparently doesn’t notice much of this. “The current bleaching wave is the first to occur during La Niña conditions,” study researcher Kate Quigley said in an interview with Scientias.nl†

Heat resistant

It may all seem very discouraging. The question therefore arises whether the beautiful Great Barrier Reef still has a future. However, according to a new study, there is light at the end of the tunnel. Quigley and her colleagues discovered that hundreds of reefs may be home to heat-resistant corals. “Finding coral reefs that can withstand global warming is a challenge,” she says. “In our study, we combined remote sensing with culture experiments to estimate coral survival after exposure to high temperatures. We then developed a method to find these heat-resistant corals among the thousands of reefs on the Great Barrier Reef. We also tried to estimate how ubiquitous they are.” And there were promising results.

Kate Quigley collects a reproductive coral colony from a heat resistant reef capable of passing this trait on to offspring. Image: Marie Roman/AIMS

According to the researchers, as much as 7.5 percent of the reefs in the Great Barrier Reef could house heat-resistant corals. “It means these reefs are home to resilient corals that can transfer heat tolerance to their offspring,” Quigley explains. Resilient corals are actually corals that experience mild or severe stress, but do not die. They may show signs of stress or illness, but then bounce back and recover. “This suggests that even if the warming is severe and some damage or death occurs, the surviving corals should be able to produce offspring that can survive the warming within a certain range (~3 degrees Celsius).”

Promising

They are particularly rosy findings during a bleak event. “These results offer hope that the Great Barrier Reef is more resilient than previously thought,” said Quigley. However, according to her, we should not celebrate too soon. “At this point, we don’t know exactly how many heat-resistant corals are needed to make the entire ecosystem more resilient,” she explains. “That’s because the Great Barrier Reef is about the same size as Italy. It is essentially simply a matter of scale.” Still, the discovery that 7.5 percent of reefs may harbor heat-resistant corals is a relief. “It’s a welcome surprise,” Quigley says. “It gives us hope that heat tolerance is widespread in the Great Barrier Reef. Possibly this is not just a special feature of the reefs located in the far northern tip, as previously believed.”

recovery

The knowledge gained in the study can now help researchers make vulnerable reefs stronger. Thanks to the results, for example, coral reefs that are resistant to global warming can be more easily identified. These could then be used to restore degraded and damaged reefs. And so the Great Barrier Reef is not lost yet.

The study’s findings suggest that some gritty corals may well survive despite disastrous massive bleaching waves. “We shouldn’t be complacent, though,” Quigley underlines. “Warming is becoming more and more extreme, which means that heat stress is also increasing dramatically.” According to Quigley, more action is required to save coral from destruction. For example, CO2 emissions are the main problem that needs to be addressed to prevent coral reefs from further bleaching and dying. “Strong climate change policies are needed to immediately reduce our emissions,” she says. “Because simply relying on the speed at which the coral adapts may not be enough.”