It's Happening Now - Shells Of Tiny Marine Snails, Key To Ocean Food Chain, Are Already Dissolving
The canaries foretelling ocean acidification fly through the water on winglike feet, lofting their tiny curl of a shell behind them. And those shells are dissolving. For more than a decade, laboratory studies and models have warned of the vulnerability of pteropods—tiny sea snails also known as sea butterflies—to ocean acidification. Now those predictions have escaped the lab. From the Gulf of Alaska and the Bering Sea to the Beaufort Sea, scientists are finding pteropods with dissolved shells. Nina Bednarsek, a biogeochemist with the Southern California Coastal Water Research Project, recently presented some of these findings at the Alaska Marine Science Symposium.
Bednarsek’s latest field observations show dissolving pteropod shells from a yawning hotspot of corrosive water that encompasses their spawning grounds in the western Gulf of Alaska. In the Canadian Beaufort Sea, the picture is even more troubling. There, in fjords where ocean acidification is exacerbated by glacial meltwater, up to 70 percent of the animals have corroded shells.
Since the Industrial Revolution, 40 percent of the carbon dioxide released from the burning of fossil fuels has been absorbed by the oceans. The excess carbon dioxide makes the water more acidic, causing calcium carbonate (the compound used by many organisms to build shells or other structures) to dissolve more easily. Since pteropods build thin shells from the most soluble form of calcium carbonate, they’ve long been studied in ocean acidification research. In laboratory experiments, researchers bubble carbon dioxide into vials containing the tiny creatures. They track how the shells degrade, and even crumble, in the most extreme treatments.
Hundreds of meters down, the whole ocean is corrosive to these delicate sea snails. The region of pteropod-friendly water near the surface is shallower in cold water, which can absorb more carbon dioxide, and in places like the northern Pacific Ocean, where circulation brings naturally more acidic water closer to the surface. Seasonal patterns of currents and upwelling have always brought some of this water within the range of pteropods, but the rapid increase in anthropogenic carbon dioxide is expanding the sea snails’ exposure to harmful conditions.
Scanning electron microscope examinations of pteropod shells show how the calcium carbonate dissolves in acidified water. In the first image, a healthy shell is smooth and full, while in the second, a closer zoom on a shell that had been exposed to acidified water shows it to be rough and pockmarked. Images by Nina Bednarsek
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https://www.hakaimagazine.com/news/the-shells-of-wild-sea-butterflies-are-already-dissolving/
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