Conservationists have started a campaign to urge the Australian government to formally protect the Coral Sea, one of the country's last tropical marine wildernesses.  A coalition, led by the World Wildlife Fund, has declared it a 'predator diversity hotspot' for its abundant shark populations.  The environmental groups are concerned the area could be damaged by a variety of man-made threats. Phil Mercer reports from Sydney.

Conservationists describe the Coral Sea as "a stunning blue-water highway, full of oceanic predators."

It is a haven for hammerhead and white tip sharks, as well as manta rays.

The Coral Sea covers 780,000 square kilometers and borders the Great Barrier Reef off Australia's east coast.

Wildlife groups want the government in Canberra to give it full environmental protection and create what would be the world's largest marine park.

Gilly Llewellyn, from the conservation organization WWF, says pollution and oil and gas drilling are among many threats that could damage the Coral Sea's ecosystem.

"It could potentially be targeted by illegal fishermen," Llewellyn said. "Sharks are increasingly rare in our oceans today.  These are the sort of lions and tigers of the sea and,  unfortunately, they're prized for their shark fin, which commands a high price in the Asian marketplace.  And so, you know, illegal fishers, looking for sharks for their fin, are becoming increasingly bold. So, without formal protection for the Coral Sea we're afraid it might be vulnerable to that in the future."

Environmentalists point to the alarming statistic that coral reefs are declining five times faster than the rainforests.

The Coral Sea is considered one of the most spectacular scuba diving destinations in the world, partly because there are so many sharks within the system of reefs.

An Australian government spokesman says a panel of experts is reviewing protection options.