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A tiny marine snail that grows no bigger than a lentil supports an entire community of animals in the southern oceans. But the food chain is in danger of collapse, because warmer seas are making it impossible for the snail to survive.
Scientists have found that, as the seas around Antarctica become warmer and more acidic, pteropod snails, which are the ultimate food source for everything from fish and seals to penguins and whales, are at a greater risk of being wiped out.
A study has found that at the current rate at which the southern oceans are becoming more acidic - due to a rise in atmospheric carbon dioxide - it will be impossible for the snails to make their shells from the middle of this century.
The pteropods are victims of "double jeopardy" because as the snails try to compensate for more acidity, they are less able to cope with warmer temperatures, says Gretchen Hofmann of the University of California at Santa Barbara. "They are harbingers of change. It's possible by 2050 they may not be able to make a shell anymore. If we lose these organisms, the impact on the food chain will be catastrophic."
Pteropods are known as the "potato chip" of the oceans because they are eaten by so many species.
The snails make their shells from minerals found in seawater but the chemistry involved can only take place when the water is not too acidic.
However, the build-up of carbon dioxide levels in the atmosphere is causing more of the gas to dissolve in the oceans to form carbonic acid.
The rate of increase in ocean acidity is faster than at any time in the past tens of millions of years and the problem will last for centuries, says Doney Scott of the Woods Hole Oceanographic Institution.
"Laboratory experiments show that acidification directly harms many marine species by reducing shell formation, slowing growth rates and hindering reproduction.
"It is likely that the ocean of the future under high carbon dioxide will look quite different within the lifetimes of today's children if we continue on our current course."
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