Scientists warned earlier this year that high ocean temperatures linked to global warming had caused severe coral bleaching in parts of the reef, said to be one of the seven natural wonders of the world.

Bleaching occurs when the plant-like organisms that make up coral die and leave behind the white limestone skeleton of the reef.

"We're very concerned because this is a 5.8-billion-dollar (4.5-billion-US) tourist industry on the reef employing 33,000 people," Bailey told the Australian Broadcast Corporation.

"So, obviously, we're tackling this issue from both ends -- the cause of the problem and also trying to find very practical ways where we can mitigate the problem."

The shade cloth, which is being developing by marine researchers in Queensland, would be held in place by floating pontoons.

Marine biologist Russell Hore from Reef Biosearch in Port Douglas said while the idea had at first seemed laughable, everything had to be considered to protect the UNESCO World Heritage-listed reef from future bleaching.

"We haven't had the full effects that some places around the world have had, but it's really just a matter of time and if we don't start to seriously look at this issue then we certainly could be looking at large areas of coral reefs around the world dying off," he said.

Although it would be impossible to shade the entire reef, which stretches over more than 345,000 square kilometers (133,000 square miles), the trial of four five-metre square shade cloths was about proving coral bleaching could be tackled by reducing both light intensity and temperature, he said.

The development follows Thursday's proposal by scientists to protect strategic areas of the reef from bleaching by spraying the water's surface with a mist of seawater to break surface tension and reduce the UV radiation reaching the coral beneath.

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