Australia's Great Barrier Reef Marine Park Authority (GBRMPA) on Thursday confirmed "widespread coral bleaching" is occurring on the reef.
Aerial surveys showed that "some southern areas of the Reef that had little or no bleaching in 2016 and 2017 have now experienced moderate or severe bleaching," the authority said.
Warmer temperatures, particularly in February, led to the latest bleaching, the GBRMPA said. Bleaching does not automatically mean the corals will die. Mildly or moderately affected reefs usually recover.
Key tourism reefs in northern and central areas should survive, the authorities said.
Ocean warming in 2016 and 2017 killed almost half the coral.
The Great Barrier Reef is the world's largest coral system. Climate change remains the greatest threat to the reef, according to the GBRMPA.
rt/sms (dpa, GBRMPA)