Disturbing Great Barrier Reef photo hints at 'ironic' problem

When it comes to the Great Barrier Reef, it sometimes feels like it’s all bad news. And while there are sometimes glimmers of hope about sections of the reef recovering, disturbing new images reveal sections of this regrowth are now dying.

Bleaching over the 2023-2024 summer has impacted newly formed varieties that grew back after the consecutive bleaching events in 2016 and 2017. Most of them are from the genus Acropora which are able to grow back faster than larger varieties — but unfortunately these smaller corals are not heat resistant.

Great Barrier Reef expert Professor Terry Hughes has shared images from James Cook University (JCU) showing widespread die-off close to Lizard Island on the northern end of the reef. “It has severely bleached at a comparatively modest level of heat exposure because it’s now populated by the most vulnerable corals,” he told Yahoo News.

Read more: What is coral bleaching?

Hughes is concerned these Acropora species are responsible for most of the recent coral recovery on reefs that escaped bleaching in 2020 and 2022. "The rapid recovery somewhat ironically has made those reefs more vulnerable to heat exposure. So the reefs that have bleached the least this time are the ones with lower amounts of recovery," he said.

What does coral regrowth mean?

As director of the Australian Research Council's Centre of Excellence for Coral Reef Studies at JCU, Hughes is adept at explaining coral bleaching. But when it comes to talking about coral “recovery”, he concedes the term can be confusing to many. Generally speaking it can refer to either bleached corals regaining colour, or the regrowth of depleted populations.

“But probably the most comprehensive definition of recovery would be reassembly of the original mix of species and sizes and ages with corals,” Hughes said. “And that's simply not happening anymore, because the gap between one (bleaching event) and the next is too short for that to happen. Particularly with loss, albeit at a lower rate, of the long lived tougher corals compared to the short with fast growing ones.”

Why the Great Barrier Reef is becoming unstable

Hughes is concerned sections of the Great Barrier Reef are becoming “increasingly unstable” because the gaps for recovery are shrinking as mass bleaching events become more frequent. On top of that, areas that have died and then been recolonised by Acropora are more vulnerable to future bleaching and are at risk of dying young — those photographed near Lizard Island are likely less than seven years old.

“During the early events, there was a very clear relationship between where the heat was and where the corals were bleaching and dying. That relationship is getting more complicated because it's now driven by the history of not just the current bleaching event, but the one before it,” Hughes said.

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The term “ecological memory” is used to explain the process of previous bleaching events shaping future ones. Understanding how these recurring climate events impact ecosystems is now a challenge researchers face.

“We don't have the luxury of studying them one at a time as a single unprecedented event. We've got to figure out what five bleaching events do to the Barrier Reef. It’s a complicated story,” Hughes said.

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