Climate change

Sixth mass coral bleaching event confirmed on Great Barrier Reef

Written by Oceanographic Staff

The Great Barrier Reef Marine Park Authority (GBRMPA) confirmed that the reef has been hit by the sixth mass coral bleaching event due to the effects of climate change.

Aerial surveys of around 750 reefs that were conducted by helicopters and fixed-wing aircraft across 1,200km have shown extensive bleaching activities across the Great Barrier Reef, according to the GBRMPA and the Australian Institute of Marine Science (AIMS). The mass bleaching event is the first to happen under the La Niña weather phenomenon which was thought to offset warming ocean temperatures by bringing cooler water to the region.

Neal Cantin, an AIMS coral biologist, said: “More than half of the living coral cover that we can see from the air is severely bleached completely white and can have signs of fluorescence in the colors of pink, yellow and blue. The corals are producing these fluorescent pigments in an attempt to protect their tissue from heat and from the intense sun during these marine heatwaves.”

The aerial survey found the worst bleaching near Townsville in northeastern Queenland, while areas near Cairns and Port Douglas have been less affected. The scientists believe this is due to lower levels of heat stress in those regions.

Coral bleaching events happen when the water is too warm. Corals then tend to get stressed and expel algae that is living in their tissues, depriving it of a food source. If water conditions don’t improve, corals can starve and die which turns them white as its carbonate skeleton is exposed.

“Even the most robust corals require nearly a decade to recover,” said Jodie Rummer, associate professor of Marine Biology at James Cook University in Townsville. “So we’re really losing that window of recovery. We’re getting back-to-back bleaching events, back-to-back heat waves. And, and the corals just aren’t adapting to these new conditions,” she said.

The sixths mass bleaching event is the first since 2020 and the fourth mass bleaching event in six years. However, it is important to remember that a bleached coral is not automatically dead. They can survive bleaching events, while studies have confirmed that heat stress cans slow coral growth, limit their spawning abilities and make them more susceptible to diseases. David Wachenfeld, chief scientist at the GBRMPA, explained: “If the water temperature decreases, bleached corals can recover from this stress. It is important to remember that we had a mass bleaching event in 2020, but there was very low coral mortality.”

To decrease water temperatures and limit the widespread effects of climate change on corals, scientists believe that more needs to be done to tackle climate change. Wachenfeld added: “The reef remains a vast and resilient ecosystem. Despite the concerns that we have when we see a climate-driven impact like this, we have to maintain determination and hope for the future. But that determination and hope has to be based on the strongest and fastest possible action to reduce greenhouse gas emissions globally and the ongoing commitments of governments, the community and industry to protect the system.”

A ten-day monitoring mission by UNESCO is currently looking at the possibility of adding the Great Barrier Reef to their ‘in danger’ list in the hopes of encouraging the Australian government to protect the site. In the past, the Australian government has been criticised of its strong support of the fossil fuel industries and not doing enough to tackle climate change

Amanda McKenzie, CEO of the Climate Council, said in a statement: “It’s time to end fossil fuel subsidies and stop the expansion of oil and gas exploration. To give our reef a fighting chance, we must deal with the number one problem: climate change. No amount of funding will stop these bleaching events unless we drive down our emissions this decade.”

For more from our Ocean Newsroom, click here.

Photography courtesy of the Ocean Image Bank/The Ocean Agency.

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