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‘There is no time to lose’: Great Barrier Reef has lost half its corals

There is no time to lose – we must sharply decrease greenhouse gas emissions ASAP

Study authors

“The loss of big corals is important because they make all the babies – they’re responsible for a huge proportion of the breeding that’s done every year by adult corals,” Professor Hughes said.

The climate crisis has driven marine heatwaves, with the research recording steeper deterioration of coral colonies in the northern and central Great Barrier Reef after mass coral bleaching in 2016 and 2017.

Dead coral at the Great Barrier Reef.

Dead coral at the Great Barrier Reef. Credit:Tony Chase

The southern part of the reef was also exposed to record-breaking temperatures and extensive bleaching in early 2020 (this data was not included in the study).

Corals rely on algae known as zooxanthellae to provide the bulk of their energy and much of their vibrant colour. When exposed to sustained abnormal heat – measured in so-called degree-heating days – corals begin to expel the algae, leading to mass bleaching.

Branching and table-shaped corals provide shelter and habitat for reef inhabitants such as fish, and their loss reduces fish abundance and the productivity of coral reef fisheries.

Bleaching on the Great Barrier Reef corals near Cooktown in March 2020.

Bleaching on the Great Barrier Reef corals near Cooktown in March 2020.Credit:Via Terry Hughes

“These types of corals are three-dimensional – they make the nooks and crannies that are essential for the biodiversity of the coral reef,” Professor Hughes said.

Better data on the demographic trends of corals is needed to understand how their populations are changing, the researchers found.

“We used to think the Great Barrier Reef is protected by its sheer size—but our results show that even the world’s largest and relatively well-protected reef system is increasingly compromised and in decline,” Professor Hughes said.

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The authors are concerned about the shrinking gap between bleaching events because there is little opportunity for corals to rebound.

“There is no time to lose – we must sharply decrease greenhouse gas emissions ASAP,” the research paper states.

Global temperature increases would need to stabilise between 1.5 and two degrees for the reef to remain, even if it was quite different to what exists now, Professor Hughes said. “If it’s three or four degrees then forget about it.”

This year, February had the highest monthly sea surface temperatures ever recorded on the Great Barrier Reef since the Bureau of Meteorology’s records began in 1900.

The warming ocean is affecting reefs worldwide, including off the coast of Brazil, in parts of Melanesia and Indonesia.

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