The latest survey reveals the shocking extent of Great Barrier Reef bleaching during a year associated with cooler ocean temperatures. 

More than 90% of the corals surveyed along the Great Barrier Reef this year were bleached, according to a report that was quietly published by Australian government scientists, confirming its sixth mass bleaching event on record. 

The Great Barrier Reef Marine Park Authority released the findings on a late evening on May 10 after weeks of delay, saying that above-average water temperatures in late summer had caused coral bleaching throughout the world’s biggest coral reef system. The most severe bleaching occurred in the central region between Cape Tribulation and Whitsunday, areas that are most visited by tourists. Inshore and offshore reefs were also badly impacted. 

“The surveys confirm a mass bleaching event, with coral bleaching observed at multiple reefs in all regions,” a statement accompanying the report said. “This is the fourth mass bleaching event since 2016 and the sixth to occur on the Great Barrier Reef since 1998.”

The reef, which covers about 350,000 square kilometres – larger than the UK and Ireland combined – has already undergone five mass bleaching events in 1998, 2002, 2016, 2017 and 2020. The events in 2016 and 2017 were so severe that it cost the death of 50% of Australia’s iconic reef.

Coral bleaching occurs as a heat stress response from rising ocean temperatures, which drives algae away from coral reefs, causing reefs to lose their vibrant colours. While bleaching can naturally occur, this is the first time the Great Barrier Reef experiencing extreme coral bleaching during La Niña, an oceanic phenomenon that is associated with cooler Pacific Ocean temperatures, highlighting worsening global warming. 

“Although bleaching is becoming more and more frequent, this is not normal,” said Lissa Schindler, a campaign manager with the Australian Marine Conservation Society. “We should not accept that this is the way things are. We need to break the norms that are breaking our reef.”

While coral bleaching is a clear indicator of rapidly rising ocean temperatures and impacts to marine life, corals can survive and recover from these bleaching events. But as these heat stresses become more frequent and long-lasting, corals are more susceptible to diseases, slowing down their recovery and limiting their ability to spawn.

Still, David Wachenfeld, chief scientist of the Great Barrier Reef Marine Park Authority remains cautiously optimistic, saying that early indications show that the mortality rates won’t be very high from this mass bleaching event. 

The survival of the iconic landmark and important marine ecosystem will therefore depend on drastic greenhouse gas emission cuts within the decade, a topic that could determine the upcoming Australian elections on May 21. 

Prime Minister Scott Morrison’s conservative Liberal Party aims to reduce Australia’s emissions by 26% to 28% below 2005 levels by 2030, while the opposition Labor Party is setting a more ambitious target of cutting emissions by 43% by the end of the decade.

Read more: Great Barrier Reef Should Be Listed as Endangered, UN Says. Australia Disagrees