Marine heatwave causes mass bleaching on Australia's Great Barrier Reef: report

Coral bleaching in Australia's iconic Great Barrier Reef has been linked to a "marine heatwave".

In a report published late on Tuesday, government scientists found that coral bleaching affected 91 percent of 719 reefs assessed along the Great Barrier Reef over the summer of 2021-22.

Coral bleaching is a phenomenon that occurs when coral become stressed due to changing conditions and expel the algae that live inside their tissue, causing the coral to become white.

Bleached coral face a higher risk of starvation and disease.

The summer of 2021-22 marked the sixth mass bleaching event on the Great Barrier Reef since 1998, four of which have occurred since 2016.

Tuesday's report from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australian Institute of Marine Science (AIMS) and Great Barrier Reef Marine Park Authority revealed the reef's mean sea surface temperature was 0.4 degrees Celsius above average in some parts.

"Above-average water temperatures led to a mass coral bleaching event late in the summer," it said.

"Compared to previous summers, cumulative impacts were limited this summer, with one major pressure, a marine heatwave, dominating."

The bleaching occurred despite Australia experiencing a milder summer than usual due to a La Nina event.

Tuesday's report noted that climate change "remains the greatest threat to the reef."

"The events that cause disturbances on the reef are becoming more frequent, leaving less time for coral recovery," it warned.