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 that are the ultimate food source for everything from fish and seals to penguins and whales are at 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, said Gretchen Hofmann of the University of California at Santa Barbara. “These animals are not charismatic but they are talking to us just as much as penguins or polar bears,” Professor Hofmann told the American Association for the Advancement of Science.
“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,” she said.
Pteropods are known as the “potato chip” of the oceans because they are eaten by so many species. Fish that feed on pteropods are eaten by bigger fish, seals and penguins, which are eaten by killer whales.
The snails make their calcium carbonate shells from minerals found in seawater but the chemistry involved can only take place when the water is not too acidic.
But, 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 many centuries, said 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,” Dr Scott said. “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.”
Pteropods are particularly vulnerable to warmer, acidic seas because they live in an environment where temperatures and acidity do not fall outside a certain range. “For pteropods, that’s the only place they can reside. There is no place for them to go to because of this temperature boundary,” Dr Scott said. “They cannot move closer to the equator where things may be happier for them from an acidity point of view, because it’s too warm for them.”
Dr Hofmann said pteropod snails could “re-tune” their metabolism to cope with rising acidity but this comes at a cost – they are less able to withstand warmer temperatures and they grow smaller.
Steve Connor, The Independent, 19 February 2008. Article.
