Acidified waters off Hokkaido threaten survival of ‘ice angels’

Clione, translucent sea slugs dubbed “angels in drift ice,” could be wiped out off eastern Hokkaido because increasingly acidic seawater from carbon dioxide emissions is destroying their sole food source, studies show.

In waters of Japan’s northernmost main island, Clione limacine, a 2-centimeter-long variant also known as the naked sea butterfly, feast on a small sea snail species called Limacina helicina, whose clear, glass-like shells measure 3 to 5 millimeters in diameter.

Katsunori Kimoto, a senior researcher at the Japan Agency for Marine-Earth Science and Technology, said the snails’ shells are dissolving and developing holes in the Arctic Ocean.

Kimoto said higher concentrations of airborne CO2 from human activities, such as burning fossil fuels, have increased the volume of CO2 that dissolves in seawater.

The resultant chemical reactions have decreased the hydrogen-ion concentration measured in pH in oceans.

According to the Japan Meteorological Agency, the pH level for surface seawater around the world is about 8.1, meaning the alkaline level is still strong. But the figure is projected to reach a more acidic 7.7 by the end of this century.

The phenomenon is making it difficult for Limacina helicina to maintain a healthy external structure because its shell is made of calcium carbonate, which is vulnerable to dissolving in high acidity levels.

Tomoyuki Yamamoto, The Asahi Shimbun, 27 March 2023. Full article.

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