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The Great Barrier Reef has lost half its corals in just 20 years, study says

The population of corals within Australia’s Great Barrier Reef has plummeted by 50 percent in the last two decades, according to a new study published on Wednesday.

Researchers from the ARC Centre of Excellence for Coral Reef Studies in Queensland, Australia, assessed the colony size of corals in the reef — the world’s largest — between 1995 and 2017, and found a drastic depletion in the population of small, medium and large coral.

“The decline occurred in both shallow and deeper water, and across virtually all species, but especially in branching and table-shaped corals,” study co-author Professor Terry Hughes said of the findings, published in the Royal Society journal.

These specific corals are especially important in providing a habitat for marine life such as fish that inhabit the reef, the researchers said, meaning their loss also results in a decline in reef biodiversity. Despite covering less than 0.1 percent of the ocean floor, reefs host more than 25 percent of all marine fish species, according to the International Union for the Conservation of Nature, a network of government and civil society organizations.

“These were the worst affected by record-breaking temperatures that triggered mass bleaching in 2016 and 2017,” Hughes added.

Coral reefs contain remarkable biodiversity, but the vast majority face being wiped out as the planet continues to warm. David Gray / Reuters file

Coral bleaching occurs as a result of the reef experiencing warmer than usual sea temperatures. Climate change has dramatically increased the frequency of these events which inhibits the reef’s ability to recover. A 2019 report by the U.N.’s Intergovernmental Panel on Climate Change warned that reefs can take more than 15 years to recover, yet further mass bleaching — the third event in just five years — occurred again this year.

“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,” Hughes said.

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Coral reefs — which harbor the highest biodiversity of any ecosystem on earth — are some of the most vulnerable environments to the climate crisis. The U.N. report warned that the vast majority of all tropical reefs on earth will disappear even if global warming is limited 2.7 degrees Fahrenheit; an aspiration that looks increasingly unlikely to be achieved.

The earth has already warmed over 1.8 degrees above pre-industrial levels with current estimates suggesting that the world is on track for between 3.6 and 4.4 degrees of warming.

“There is no time to lose, we must sharply decrease greenhouse gas emissions as soon as possible,” the study authors concluded.

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The Great Barrier Reef has lost half its corals

Australia’s Great Barrier Reef has lost 50% of its coral populations in the last three decades, with climate change a key driver of reef disturbance, a new study has found.



a turtle swimming under water: Coral reefs are some of the most vibrant marine ecosystems on the planet, with up to a third of all marine species relying on them at some point in their life cycle.


© Jonas Gratzer/LightRocket/Getty Images
Coral reefs are some of the most vibrant marine ecosystems on the planet, with up to a third of all marine species relying on them at some point in their life cycle.

Researchers from the ARC Centre of Excellence for Coral Reef Studies, in Queensland, northeastern Australia, assessed coral communities and their colony size along the length of the Great Barrier Reef between 1995 and 2017, finding depletion of virtually all coral populations, they said Tuesday.

Coral reefs are some of the most vibrant marine ecosystems on the planet — between a quarter and one third of all marine species rely on them at some point in their life cycle.

The Great Barrier Reef, the world’s largest coral reef, covers nearly 133,000 square miles and is home to more than 1,500 species of fish, 411 species of hard corals and dozens of other species.

“We found the number of small, medium and large corals on the Great Barrier Reef has declined by more than 50% since the 1990s,” reported co-author Terry Hughes, a distinguished professor at the ARC Centre 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 dies.

Coral population sizes are also considered vital when it comes to the coral’s ability to breed.

“A vibrant coral population has millions of small, baby corals, as well as many large ones– the big mamas who produce most of the larvae,” said Andy Dietzel, a doctoral student at the ARC Centre of Excellence for Coral Reef Studies, in a statement.

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“Our results show the ability of the Great Barrier Reef to recover — its resilience — is compromised compared to the past, because there are fewer babies, and fewer large breeding adults,” he added.

Population declines occurred in both shallow and deep water coral species, experts found, but branching and table-shaped corals — which provide habitats for fish — were worst affected by mass bleaching events in 2016 and 2017, triggered by record-breaking temperatures.

Warm ocean temperatures are the main driver of coral bleaching, when corals turn white as a stress response to water that is too warm. Bleaching doesn’t kill coral immediately, but if temperatures remain high, eventually the coral will die, destroying a natural habitat for many species of marine life.

Tuesday’s study found steeper deteriorations of coral colonies in the Northern and Central Great Barrier Reef following the mass bleaching events in 2016 and 2017.



underwater view of a coral: The Great Barrier Reef covers nearly 133,000 square miles.


© Francois Gohier/VWPics/Universal Images Group/Getty Images
The Great Barrier Reef covers nearly 133,000 square miles.



underwater view of a coral: Climate change is driving an uptick in the frequency of "reef disturbances," authors of the report warned.


© William West/AFP/Getty Images
Climate change is driving an uptick in the frequency