What’s eating the sea butterfly?



AGENCIES

Published — Tuesday 27 November 2012

Last update 27 November 2012 1:08 am

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Rising acidity is eating away the shells of tiny snails, known as “sea butterflies,” that live in the seas around Antarctica, leaving them vulnerable to predators and disease, scientists said Sunday.
The study presents rare evidence of living creatures suffering the results of ocean acidification caused by rising carbon dioxide levels from fossil fuel burning, the British Antarctic Survey said in a statement.
“The finding supports predictions that the impact of ocean acidification on marine ecosystems and food webs may be significant.”
The tiny snail, named for two wing-like appendices, does not necessarily die as a result of losing its shell, but it becomes an easier target for fish and bird predators, as well as infection.
This may have a follow-through effect on other parts of the food chain, of which they form a core element.
The world’s oceans absorb more than a quarter of man-made carbon dioxide emissions, which lower the sea water pH.
Since the beginning of the industrial era, our oceans have become 30 percent more acidic, reaching an acidity peak not seen in at least 55 million years, scientists say.
Scientists discovered the effects of acidification on the sea butterflies from samples taken around the Scotia Sea region of the Southern Ocean in February 2008.
The sea snails are an important source of food for fish and birds as well as an indicator of marine ecosystem health.
But until now, there has been little evidence of the impact of ocean acidification on such live organisms in their natural environment and the study supports predictions that acidification could have a significant effect on marine ecosystems.
The researchers examined surface water, where wind causes cold water to be pushed up from deeper water, because it is usually more corrosive to a particular type of calcium carbonate which the sea snails use to build and maintain their shells.
Climate models forecast more intense winds in the Southern Ocean this century if CO2 continues to increase, which will make the mixing of deep water with more acidic surface waters more frequent, the study said.
This will make calcium carbonate reach the upper surface layers of the Southern Ocean by 2050 in winter and by 2100 all year round, said the study’s co-author Dorothee Bakker, research officer at the University of East Anglia.
Since the start of the industrial revolution, the acidity of surface ocean waters has increased by 30 percent, according to NOAA research.
If CO2 levels continue to rise in the future, surface waters could be almost 150 percent more acidic by the end of this century, which has not been experienced for more than 20 million years.

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