Australia, are known to increase stress on fish.
Photo Credit: Reuters/Ho New
ABC News (Australia), December 1, 2010
Australian scientists fear the planet is on the brink of another mass extinction as ocean dead zones continue to grow in size and number. More than 400 ocean dead zones - areas so low in oxygen that sea life cannot survive - have been reported by oceanographers around the world between 2000 and 2008. That is compared with 300 in the 1990s and 120 in the 1980s.
Professor Ove Hoegh-Guldberg, of the ARC Centre of Excellence for Coral Reef Studies (CoECRS) and from the University of Queensland, says there is growing evidence that declining oxygen levels in the ocean have played a major role in at least four of the planet's five mass extinctions.
"Until recently the best hypothesis for them was a meteor strike," he said."So 65 million years ago they've got very good evidence of the cretaceous exctinction event."But with the four other mass extinction events, one of the best explanations now is that these periods were preceded by an increase of volcanic activity, and that volcanic activity caused a change in ocean circulation.
"Just as we are seeing at a smaller scale today, huge parts of the ocean became anoxic at depth. "The consequence of that is that you had increased amounts of rotten egg gas, hydrogen sulfide, going up into the atmosphere, and that is thought to be what may have caused some of these other extinction events."
Professor Hoegh-Guldberg says up to 90 per cent of life has perished in previous mass extinctions and that a similar loss of life could occur in the next 100 years. "We're already having another mass extinction due to humans wiping out life and so on, but it looks like it could get as high as those previous events," he said. "So it's the combination of this alteration to coastlines, climate change and everything, that has a lot of us worried we are going to drive the sixth extinction event and it will happen over the next 100 years because we are interfering with the things that keep species alive.
"Ocean ecosystems are in a lot of trouble and it all bears the hallmarks of human interference. We are changing the way the Earth's oceans work, shifting them to entirely new states, which we have not seen before."
He says while it is impossible to predict the future, in a century from now the world will be vastly different. "A world without the Great Barrier Reef, where you don't have the pleasure of going to see wild places any more," he said. "We might be able to struggle on with much lower population densities, but ultimately it won't be the world we have today.
"The idea of walking in the Daintree will be a forgotten concept because these changes have occurred."