On Western Australia's Ningaloo Reef, the shift from stark white to sickly brown paints a dire picture.

"It's a really dramatic change from all the colour and the vibrancy that a healthy coral shows," marine scientist Zoe Richards said.

"We've shifted to this dull phase where it's algae dominating the corals."

The most recent survey by researchers from Curtin University shows that more than 60 per cent of corals at eight sites, largely in the reef's northern lagoon, have died.

Of the 1,600 corals counted in March , only 600 were still alive come late October.

The findings mark a new phase for the World Heritage site, which was gripped by its worst-ever bleaching event earlier this year.

Scientists warn ocean temperatures off WA are already warmer than average, with the summer mon

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