Dead calm: John Rumney from Great Barrier Reef Legacy looking at bleaching corals off Port Douglas this week. Credit:Dean Miller, GBR Legacy Mr McKenzie said wholesalers were getting nervous but it could take until September to know how hard the impact will be on an industry worth $6 billion a year and employs perhaps 60,000 people. In terms of visitor numbers it just had its best year. (See Great Barrier Reef Marine Park Authority chart below.) To be sure, Australia's reefs are among many being hit by excessively warm ocean waters that scientist say began to devastate coral reefs around the planet almost three years ago with little sign of an end.

Beyond a certain temperature, corals expel the zooxanthellae algae that provide them both energy and colour. In 2016, two-thirds of the corals on the most pristine reefs north of Port Douglas died, and even though the central region around Cairns had relatively mild bleaching it was still the worst on record. Illustration: Matt Golding 'What's it going to take?' The unprecedented back-to-back bleaching is fuelling calls from within the industry to stand up for the reef's future, including taking on the Queensland and federal governments for their support for the development of a huge new coal province in the Galilee Basin for export.

"If this isn't going to kick people in the arse, what's it going to take?" said John Edmondson, a marine biologist and owner of Wavelength, a company that operates reef tours from Port Douglas. Oddly, the first phase of starvation often makes the corals even more beautiful – the fluorescent pinks and purples can wow tourists before the corals become deathly white and are ultimately covered in ugly green algae that may portend their demise. Ed and Elaine Baroth, visiting from Los Angeles, said marine biologists aboard their day out on a Wavelength tour "made a point of pointing out the dead corals – the whole luncheon talk was about it". Even with the bleaching, the visit was "fantastic", with four sea turtles, a reef shark and a giant claim among the snorkelling highlights. "It's still like looking at a BBC documentary," Ms Baroth said. During a trip out to the reef this week, Taylor Simpkins, a marine biologist from California and working for Wavelength, said visitors were "looking into the face of climate change".

After guiding snorkellers over the offshore Opal Reef this week, Ms Simpkins was dismayed by what she saw. "This used to be my most favorite place in the world," she said. "Now maybe 20 per cent of the corals are OK." 'Didn't hear about it' Visitors with some other operators, though, said the issue of bleaching was downplayed if discussed at all. Nidhin and Sandhya Narayanan visiting Port Douglas from Adelaide said they knew about the bleaching before joining a tour with the region's biggest operator, Quicksilver. "It wasn't a shock but we didn't hear about it on the boat," Ms Narayanan said.

To the south, Hayato Kawano, a recently graduated environmental science student from Nagasaki in Japan, also reported a mixed experience from this trip off Cairns. "The weather is good, the sea is good but the coral reef had almost died in the swimming area," he said. An employee with Calypso, another operator at Port Douglas, said staff were growing more concerned about the impact of the bleaching. "We had one NASA climate scientist saying he was here to see the reef before it was gone," the employee said. However, Tony Baker, managing director of Quicksilver, said bleaching corals didn't "automatically mean they would die", adding he thought the event was "not substantially different from what we'd normally see at this time of year".

He said the industry was diverse and some operators were using a "see it before it's gone" approach as a marketing gambit. Some operators said governments here and abroad had no choice but to leave most of the remaining fossil fuels in the ground if they still wanted a reef worthy of travelling across the world to see. Loading When asked whether there was "last chance tourism" at play, Steve Edmondson - the brother of John, who runs Sailaway tours from Port Douglas - said: "It's more like last chance politics." The author travelled to the Great Barrier Reef as a guest of the Climate Council.