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Changing ocean chemistry may threaten Antarctic food chain

A sea snail, magnified about 50 times, bares the characteristic white marks of shell dissolution around its centre Photo: Kevin Johnson

Researchers at the University of California in Santa Barbara have collected the first long-term evidence that links rising levels of carbon and changes in ocean chemistry in Antarctic waters to the inability of tiny animals, such as sea snails, to build the protective, shells they need to survive.

As oceans absorb carbon dioxide from the air, it makes the water more acidic, decreasing what scientists call the pH.



Pteropods, such as sea butterflies, a type of sea snail, are small organisms that play an integral role at the base of the food chain in the Ross Sea. That food chain includes predators such as Antarctic cod, penguins and Orca whales. Changes could have serious implications on the future survival of other creatures throughout the Ross Sea.

A previous study in 2014 by the US National Oceanic and Atmospheric Administration on the effect of projected ocean acidification levels on pteropods found that, as the pH levels of the world’s oceans become more acidic, their shells would begin to dissolve.

During the study, the shell of a pteropod was immersed in ocean water with the projected pH level that the oceans could reach by the year 2100. After a month and a half in the water, the shell had dissolved almost completely.


Monitoring pH levels in the Ross Sea

To monitor these changes, lead researcher Gretchen Hofmann and her team have been deploying automated ocean sensors around McMurdo Sound in Antarctica since 2010, giving them the longest continuous dataset on ocean pH in the region.

A diver deploys an automated ocean sensor in the icy waters of McMurdo Sound, Antarctica. 
Photo credit: NSF and University of California, Santa Barbara

By continuing to deploy these pH water sensors, the team hopes to gain a more complete understanding of the ocean changes and their potential effects on one of the world’s most biologically productive ecosystems, one of the planet’s few remaining marine wilderness areas.

The research is funded by the National Science Foundation.

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