Queensland scientists fear the Great Barrier Reef could be on the cusp of a mass coral bleaching event.
The Great Barrier Reef Marine Park Authority (GBRMPA) on Tuesday said it would bolster in-water field surveys and monitoring after widespread, but minor, bleaching was detected at shallow sites exposed to lots of sun.
February and March represents the highest risk period for mass coral bleaching because of hot and dry conditions.
"Sea surface temperatures are fluctuating across the 345,000 square kilometres of Marine Park, but in some areas they've ranged up to 2.5 degrees above the average for summer," said GBRMPA chairman Dr Russell Reichelt.
"This has been exacerbated by lack of cloud cover."
Added to the concern is the Bureau of Meteorology's prediction of significant above-average March temperatures.
Professor Terry Hughes, convener of the National Coral Bleaching Taskforce, said what had happened so far did not yet constitute "mass bleaching".
"We remain hopeful that there is not enough time now for the Reef to undergo a mass bleaching as it did in 1998 or 2002," he said.
But Prof Hughes said the best outcome was that the bleaching did not worsen.
The current bleaching was a "call to action", said Queensland's Environment Minister Steven Miles, who was "crossing his fingers" that the natural wonder would not see a repeat of previous mass bleaching.
"Actions we are taking as part of the Great Barrier Reef long-term sustainability plan will better improve the reef's resilience to these kinds of warming events," Dr Miles said.
He pointed to the government's $100 million commitment to protecting the reef over five years.
Dr Reichelt said the next few weeks would be critical, and the outcome was "entirely dependent" on local weather conditions, including the extent of cloud cover.
Conservationists responded with concern to the news, with Greenpeace spokeswoman Shani Tager arguing it was a clear sign Queensland needed to move away from coal.
"Our reef is on the brink," she said.
"We know reefs can recover from bleaching but only in the right conditions."
The Australian Conservation Foundation, which is challenging the federal government's approval of Adani's Carmichael mine in May, also linked the news to the coal industry.
"Climate change is warming the world's oceans, making these events more common, which is a real worry for all of us who love the reef," said CEO Kelly O'Shanassy.
