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    Acidifying Oceans Are Melting Antarctic Snails

    Written by

    Derek Mead


    The pteropod Limacina helicina, which was the focus of the study. Via Red Orbit

    We know that sea levels will rise as the world warms, but one of the other worrisome effects of climate change on our oceans is that they’re becoming more acidic thanks to increasing levels of absorbed carbon dioxide. That acidification is already having negative impacts on marine wildlife, as found by a new report that shows the shells of Antarctic snails are being corroded by acidic waters.

    The new paper, published in Nature Geoscience, finds that pteropods, a group of marine snails, are being affected by the changing chemistry of Antarctic waters. Due to oceanic chemistry, calcium carbonate — which many marine animals use for their shells — is relatively stable in shallower waters, but will dissolve in deeper, colder water. The point at which conditions change is known as the lysocline, or saturation horizon. For Antarctic pteropods, the lysocline is around 200 meters deep.

    Upwelling events, in which deeper water is mixed up to the surface, usually by winds, are naturally occurring and can be corrosive towards aragonite, the form of calcium carbonate that makes up pteropod shells. But the research team, made up of members from the British Antarctic Survey, NOAA, the US Woods Hole Oceanographic Institution, and the University of East Anglia’s school of Environmental Sciences, found that acidification is increasing the corrosive effect. Previous research suggests that upwelling events and acidification will increase due to climate change, which all means that pteropods will have weaker, more corroded shells in the future.

    Electron microscope scan shows a pteropod’s
    corroded shell. Credit: Bednarsek et al

    Why does any of that matter? Pteropods are a key link in the Antarctic food chain; by eating phytoplankton and then getting eaten by larger fish and birds, they basically package nutrients into larger packages to send up the food chain. With weaker shells, they will likely have a harder time surviving, and will possibly be more susceptible to disease.

    While the cascade effects caused by the shrinking of the base of the food chain are worrisome on their own, pteropods’ structure make them good indicators of ecosystem health. If their shells are already being quantitatively corroded, it’s reasonable to hypothesize that acidification will have negative effects on other shelled marine life. And as pieces start falling out of an ecosystem, more will follow, as we’ve seen in the collapse of coral reefs.

    The actual methods used to study the tiny pteropods involved collecting them in the Antarctic and shipping them off to be scanned by electron microscopes.

    “It took us several years even to develop a technique sensitive enough to look at the exterior of the shells under high-power scanning electron microscopes, since the shells are very thin and the dissolution pattern, subtle,” co-author Dr. Geraint Tarling of BAS told the BBC. “We are now undertaking a much more comprehensive programme completely focussed on the effects of ocean acidification, not just on pteropods but to a wider range of organisms.”

    The authors freely admit that the research is only the tip of the iceberg, and it is important to note that their sample collection was conducted in 2008. The actual pteropod situation may be different now, although considering we’ve only been pumping more carbon into the atmosphere—and thus into the oceans—the trend is likely to only get worse. And as much as we obsess over the beauty of crystal-clear tropical waters, it’s the cold, nutrient-dense polar oceans that are the power plants of the world’s marine ecosystems. (For example, migratory whales feed at higher latitudes until they’re fat enough to head to tropical waters to calve.) But if climate change causes pteropods to decline as is suggested, then those rich waters are only going to get poorer.

    Follow Derek Mead on Twitter: @derektmead.