Is the Great Barrier Reef really dead

Death wasn't the end: How the Great Barrier Reef died - and rose again

The bad news is: the world's largest coral reef is dying. Heat waves, pollution and muddy water are hard on the Great Barrier Reef off the northeast coast of Australia. The good news: It's not the first time. And after each decline the reef came back. The barrier reef has died a total of four times in the last 30,000 years, reports a working group headed by Jody M. Webster from the University of Sydney - only to be re-grown elsewhere afterwards. A total of 16 cores from the continental shelf seaward of the reef show five fossil reefs, covered in sand and mud, but once as magnificent as the current version.

The water at the base of the cores was literally running away from the reefs - sea levels sank by the height of the last glaciation, and each reef reef was farther from today's coast. The deepest shallow water corals found today are more than 120 meters below sea level. That only changed about 17,000 years ago when the water returned and new corals began to grow on the remains of the reef that had fallen dry some 5000 years earlier.

But rising water can also be fatal to a reef, writes Webster's team in "Nature Geoscience": When the great continental ice caps of the northern hemisphere collapsed and their water flooded the continental shelves, two other reefs perished 13,000 and 10,000 years ago - only to grow again soon afterwards.

However, according to the researcher's group, this is somewhat puzzling, because coral reefs are in principle able to grow with rising sea levels - and do so most of the time. But during those two periods they suddenly grew only slowly, disappeared into deeper and darker water and starved to death from lack of light. The cause is probably mud, writes the team. The drill cores showed that the water quality was particularly poor at the time the reefs died out. The cloudy broth robbed the corals of precious light, and so they lost the race with the ocean.

That is also the reason why the working group draws little hope from the study for the future of the current reef. As flexible and renewable as the reefs of the past were. The multitude of modern problems - such as rising sea levels, rising temperatures, cloudy, polluted water and overfishing - leaves little room for hope that the Great Barrier Reef will survive in the long term. But the reef has died many times. The crucial question is whether it will one day rise again somewhere else - possibly over the sunken remains of former coastal cities.