The acid krilling fields

THE Southern Ocean marine ecosystem is under serious threat from ocean acidification caused by man-made carbon dioxide emissions, a new study has found.

Experiments on krill at the Antarctic Division’s headquarters in Hobart have found the key species could be all but wiped out by rising carbon dioxide levels in the ocean.

The loss of krill would spell disaster for whales, seals and penguins that feed on the tiny but abundant crustaceans.

A third of the carbon dioxide emitted each year is absorbed by the world’s oceans.

Antarctic Division scientists So Kawaguchi and Robert King have spent five years studying the hatching rates of krill eggs under varying levels of carbon dioxide.

“The air above the Southern Ocean is currently just under 400 parts per million, which is the global average, but the seawater where krill eggs are sinking is already 500 parts per million,” Mr King said.

“We’ve applied concentrations of carbon dioxide from 1000ppm all the way up to 2000ppm to krill eggs and determined when they can hatch and when they can’t.

“When you go to 1250ppm, you get a small decrease in the hatch rate. As you go up to 1500ppm, the hatch rate further decreases. And then by 1750ppm and 2000ppm, virtually no eggs hatch at all.”

The data has been used to create maps showing which regions of the Southern Ocean could be worst affected under various carbon emission scenarios.

Mr King said the predictions under the highest level of emissions might prove to be conservative, but the implications were serious.

“If still nothing is done about emissions, by the year 2300 you can basically just wipe out krill from the Southern Ocean, the hatch rate will be about 2 per cent.

Dr Kawaguchi said krill was a critical species in the ocean food chain.

“A substantial decline in krill numbers would have disastrous implications not only for the health of the ocean environment but also on the future survival of the mammals and sea birds that rely on them,” he said.

“Antarctic krill are already experiencing changing climate stressors such as temperature rise, productivity change and declining sea ice.”

The study has been published in the distinguished international journal Nature Climate Change.

David Killick, The Mercury, 10 July 2013. Article.


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