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The Great Barrier Reef has lost half its corals

(CNN) – The Australian Great Barrier Reef has lost 50% of its coral populations in the past three decades, with climate change being a major driver of reef disruption, according to a new study.

Researchers at the ARC Center of Excellence for Coral Reef Studies in Queensland, northeastern Australia, studied coral communities and their colony sizes along the length of the Great Barrier Reef between 1995 and 2017 and found that virtually all coral populations are depleted, they said Tuesday.

Coral reefs are some of the most vibrant marine ecosystems in the world – between a quarter and a third of all marine species depend on them at some point in their life cycle.

The Great Barrier Reef, the largest coral reef in the world, covers an area of ​​nearly 133,000 square kilometers and is home to more than 1,500 species of fish, 411 types of hard corals, and dozens of other species.

“We found that the numbers of small, medium and large corals on the Great Barrier Reef have decreased by more than 50% since the 1990s,” said co-author Terry Hughes, a distinguished professor at the ARC Center of Excellence for Coral Reef Studies. in a statement.

Reefs are fundamental to the health of marine ecosystems – without them, ecosystems collapse and marine life die.

The Great Barrier Reef covers nearly 133,000 square miles.

Francois Gohier / VWPics / Universal Images Group / Getty Images

Coral population sizes are also considered important when it comes to coral breeding ability.

“A vibrant coral population has millions of small and large baby corals – the large mums that produce the most larvae,” said Andy Dietzel, a PhD student at the ARC Center of Excellence for Coral Reef Studies. in a statement.

“Our results show that the Great Barrier Reef’s ability to recover – its resilience – is compromised relative to the past with fewer babies and fewer large adult breeders,” he added.

Experts found that both shallow and deepwater coral species have seen a population decline. However, branched and tabular corals, which are fish habitats, were hardest hit by mass bleaching events in 2016 and 2017, triggered by record-breaking temperatures.

This file photo taken on September 22, 2014 shows fish swimming through the coral on Australia's Great Barrier Reef.

Climate change is driving up the incidence of “reef disruption”, warned the report’s authors.

William West / AFP / Getty Images

Warm sea temperatures are the main cause of coral bleaching when corals turn white as a stress reaction to warm water. Bleaching doesn’t kill corals immediately, but if temperatures stay high, the coral will eventually die, destroying a natural habitat for many types of marine life.

Tuesday’s study found a steeper deterioration in coral colonies in the northern and central Great Barrier Reef after the mass bleaching events of 2016 and 2017.

The Great Barrier Reef has seen several mass bleaching events over the past five years, and experts said the southern portion of the reef also saw record-breaking temperatures in early 2020.

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

The report’s authors warned that climate change is increasing the frequency of “reef disturbances” such as marine heat waves.

“There is no time to waste – we need to drastically reduce greenhouse gas emissions as soon as possible,” warned the report’s authors in the article published in the Proceedings of the Royal Society Journal.

CNN’s Helen Regan contributed to this report.

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