A third of the Great Barrier Reef’s coral suffered ‘catastrophic die-off’ during 2016 heatwave, scientists say

They warn that failure to address climate change could radically alter the ecosystem.
They warn that failure to address climate change could radically alter the ecosystem.

The Great Barrier Reef in Australia experienced a “catastrophic die-off” following an extended marine heatwave in 2016, scientists say.

According to a team of international researchers, nearly a third of the reef’s coral was killed when ocean temperatures spiked in 2016.

Terry P Hughes, director of the ARC Centre of Excellence for Coral Reef Studies (CoE) at James Cook University and lead author of the study, said: “When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die.

“Averaged across the whole Great Barrier Reef, we lost 30% of the corals in the nine-month period between March and November 2016.”

Coral reef.
Coral exhibiting response during a mass coral bleaching event (GergelyTorda/ARC Centre of Excellence for Coral Reef Studies)

The reef, according to conservation charity WWF, is home to 1,500 species of fish, 134 species of sharks and rays, six species of threatened marine turtles, and more than 30 species of marine mammals.

Using satellite imagery, scientists looked at how much coral had survived along the 2,300-km length of the Great Barrier Reef.

The study found 29% of the 3,863 reefs lost two thirds or more of their corals, affecting their ability to sustain full ecological functioning.

The northern third of the Great Barrier Reef was the most severely affected, scientists said.

Professor Andrew Baird, of Coral CoE at James Cook University, said: “The coral die-off has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining.”

Corals require warm water to thrive, but are extremely sensitive to heat.

The researchers warn that failure to address climate change – which could see global temperatures rise far above 2C – will “radically alter tropical reef ecosystems and undermine the benefits they provide to hundreds of millions of people, mostly in poor, rapidly-developing countries”.

Prof Hughes added: “The Great Barrier Reef is certainly threatened by climate change, but it is not doomed if we deal very quickly with greenhouse gas emissions.

“Our study shows that coral reefs are already shifting radically in response to unprecedented heatwaves.”

The study is published in the journal Nature.