Several reports in the journal Science suggest the only solution is to create larger, international preserves where no fishing, anchoring or collecting is allowed.

Even Australia's Great Barrier Reef, considered the cleanest and best-preserved large reef in the world, actually is not, the dozen-strong team of experts found.

"The Great Barrier Reef is already 30 percent along the way to ecological extinction," Pandolfi said in a telephone interview.

"It didn't matter if we were looking at the Red Sea, Australia or the Caribbean," added Karen Bjorndal, director of the Archie Carr Center for Sea Turtle Research at the University of Florida.

"As soon as human exploitation began, whether in the 1600s in Bermuda or tens of thousands of years ago in the Red Sea, the same scenarios were put into play."

First, people killed off large predators such as sharks and the biggest fish and turtles, which are easy to catch and slow to reproduce. Then smaller fish go and finally sea grasses and the corals themselves.

A search of historical and archaeological records in 14 regions including the Atlantic and Pacific oceans, the Red Sea, Caribbean and Australia, show the same thing - these reefs used to be teeming with life and are not any more.

HEARING THE TURTLES SPLASH

"In the 1600s when the European ships used to navigate in the Caribbean ... the ship's captain could navigate by the sounds of turtles swimming in the water, there were so many turtles swimming in the water. It is a very, very different world," Pandolfi said.

And yet, these turtles had already been decimated by indigenous populations on the Caribbean islands.

"I used to think that green turtles were basically in pristine shape when Columbus arrived, and I don't think that any more," Bjorndal said.

Agriculture alone can cause considerable damage - without people going near reefs, the analysis found.

"Back in the 1600s in Barbados when it was cleared for sugar cane farming, all the land-derived runoff was going into the reef and basically smothering the coral," Pandolfi said.

A second report in Science found that wildfires in Indonesia in 1997 may have indirectly killed an economically important reef when smoke settled onto the water, triggering a red tide - a population explosion of toxic phytoplankton.

Nerilie Abram and colleagues at Australian National University in Canberra and the Indonesian Institute of Sciences in Bandung said the problem could worsen as people clear forests, making them vulnerable to fires.

Much media and scientific attention has been paid to bleached reefs, said Pandolfi, but this damage is only the tip of the iceberg.

"What our analysis shows beyond a doubt is that problems with reefs are a lot more deeper and more fundamental ... than bleaching and disease," he said.

"It is like having a very ill person who dies not from their weak heart but from the flu," he added. "The extra stress puts them over the brink."