Record-breaking temperatures in Australia have triggered a severe coral bleaching event in the Great Barrier Reef, threatening coral survival in the World Heritage site.
Australia’s government raised the bleaching threat for the Great Barrier Reef to its highest level Sunday, after researchers said earlier this month that bleaching off the coast of northern Australia was the worst they’d seen in 15 years. This comes as Australia has been seeing strong summer and fall heat, with early March high temperatures about 4 degrees Celsius hotter than normal.
Coral bleaching occurs when stressed corals expel the symbiotic algae living in their tissues. The algae gives coral its pigment, so without it, the coral turns white. High ocean temperatures make coral more susceptible to bleaching, and bleached corals are at higher risk of death, especially if water temperatures don’t fall enough for the coral to recover.
“The corals in the remote far north of the Reef experienced extremely hot and still conditions this summer, and were effectively bathed in warm water for months, creating heat stress that they could no longer cope with,” Great Barrier Reef Marine Park Authority Chairman Russell Reichelt said in a statement.
Some surveys found up to 50 percent mortality in corals in the northern end of the reef, but Reichelt said most of the rest of the reef is in better condition. The level three threat means that the government will be “stepping up surveys” of the reef, he said.
Environmental groups like WWF called on the Australian government to take action on climate change in the wake of the bleaching event. One of the things they singled out was the Australian government’s coal mining plans — among them a massive coal mine approved by the government last October. The Carmichael coal mine, which will be located in central Queensland, will be a “complete disaster for the climate and the Great Barrier Reef,” Greenpeace Australia campaigner Shani Tager said in October. The emissions that will come from burning the coal will exacerbate ocean warming and acidification, and the mine will also lead to increased coal shipping, which will threaten the reef.
In the meantime, addressing other threats facing coral reefs will help make them more resilient to ocean warming. Reichelt said that, in addition to reducing emissions, Australia needs to tackle runoff pollution and crown-of-thorns starfish, which eat coral and which are currently experiencing an outbreak in Australia.
The Great Barrier Reef isn’t the only reef to suffer from bleaching this year. Around the world, reefs are in the midst of the third recorded global coral bleaching event, which started in 2014 and is the longest recorded bleaching event in history. The event is being exacerbated by a strong El Niño, which is heating up ocean temperatures around the world, as well as by greenhouse gas-driven climate warming.
Ocean acidification driven by higher levels carbon dioxide emissions is also impacting coral reefs — a study earlier this year found that coral grow more slowly under more acidic conditions.