An extended marine heatwave between March and November 2016 resulted in a “catastrophic” 30% reduction of living corals in the Great Barrier Reef, scientists have found.
A new study published today in the science journal Nature reveals that the coral death was closely linked to bleaching and heat exposure, with the northern third of the reef most severely affected.
This has caused radical changes to the mix of organisms living in the reef, with diverse communities transformed into degraded systems where just a few “tough species” remain.
The researchers said this reinforces the need to assess the risk of a wide-scale collapse of reef ecosystems, especially if global action on climate change fails to limit warming to 1.5-2 °C above pre-industrial levels.
“When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die,” said professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies.
“Averaged across the whole Great Barrier Reef, we lost 30% of the corals in the nine-month period between March and November 2016.”
The scientists mapped the geographical pattern of heat exposure from satellites, and measured coral survival along the 2,300-km length of the Great Barrier Reef following the heatwave.
It was found that 29% of the 3,863 reefs, comprising the world’s largest reef system, lost two-thirds or more of their corals, transforming their ability to sustain full ecological functioning.
The study is unique because it tests the emerging framework for the International Union for Conservation of Nature Red List of Ecosystems, which seeks to classify vulnerable ecosystems as ‘safe,’ ‘threatened’ or ‘endangered’.
It was also found that close to half of the corals in shallow-water have died across the northern two-thirds of the reef, although that still leaves approximately one billion corals alive.
“And on average, they are tougher than the ones that died,” Hughes continued. “We need to focus urgently on protecting the glass that’s still half full, by helping these survivors recover.”
Image credit: iStock
