Large scale coral die-offs are now occurring more frequently than at any time in the last 11 000 years, according to a new study by Australian-based scientists.

Investigations by Associate Professor John Pandolfi, of the ARC Centre of Excellence in Coral Reef Studies and The University of Queensland, of fossilized reefs in Papua New Guinea show how often the reefs were wiped out by disastrous events in past times.

"What we found was in stark contrast to what we see in the modern day," says Ass. Prof. Pandolfi. "The frequency of reef [die-off] events in the fossils is at least an order of magnitude less than it is today," he says.

Studying the fossil reefs of the Huon Peninsula, which are now cliff faces rising up to 25 metres above the beach, A/Prof. Pandolfi and his team were able to see where large scale disturbances had occurred in the history of these reefs which dated back as far as 11 000 years ago.

"The sequence of fossils is like a three dimensional movie of what happened in the reefs past," says Pandolfi.

Over the 6000 years recorded in the fossil strata the team found 4 devastating events which resulted in the death of most of the reef indicating such events had occurred about once every 1500 years.

"The cause of some of these events was volcanic, but others may have been due to bleaching, disease, or something else - we just dont know. Regardless, what is clear is that the frequency of die-off was so much lower than it is today," says Pandolfi of his findings.

The results, published in the scientific journal Geology, sound a warning bell to modern day reef management practices as todays reefs face more stress than ever.

But while the ancient reefs warn that we are seeing abnormal die-off rates, they also show that the reefs of the past recovered rapidly after these events, taking as little as 100 years to be repopulated by the corals that normally occurred there.