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    The Pacific Ocean Has Become Acidic Enough to Dissolve Sea Snails' Shells

    Written by

    Brian Merchant

    Senior Editor

    Images: NOAA

    Meet the tiny, translucent "sea butterfly," whose home is currently being transformed into an acid bath. Off the US's west coast, there are anywhere between 100 and 15,000 of these free-swimming sea snails per square meter. And the oceans are beginning to dissolve the tiny shells right off their backs. 

    A new study, among the first to examine how the process called ocean acidification impacts marine life, has confirmed that about half of all the pteropods off the west coast are fighting off the acid burn. It builds on previous work that has shown pteropods dissolving in other waters; it's a disturbing trend, considering they're a key link in the oceanic food chain.

    The world's oceans have absorbed a third of humans' carbon emissions, a process that increases their acidity. Scientists have long noted the changing chemistry of the waters, and voiced concern that this leaves calcium-based creatures, like coral and pteropods, extremely vulnerable. Now, it appears, they have proof. 

    "These are some of the first insights into how marine creatures are affected by acidification," Dr. Nina Bednarsek told me in a phone interview. She's the lead author of the National Oceanographic and Atmospheric Administration study, which was just published in the Proceedings of the Royal Society BThe research determined that "large portions of the shelf waters are corrosive to pteropods in the natural environment."

    "Fifty percent of those pteropods are affected by acidification," Bednarsek said. "It's a lot—more than we expected." And sooner. She tells me that acidification is happening sooner and on a larger scale than scientists predicted. "This is just an indication of how much we are changing the natural environment," she said.

    The study estimates "that the incidence of severe pteropod shell dissolution owing to anthropogenic [ocean acidification] has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050." In other words, thanks to human carbon pollution, twice as many marine creature shells are dissolving as were before the industrial era. And three times as many will be dissolving by mid-century. 

    Image: NOAA

    This is worrisome, not just because it's kind of horrifying on a micro-level—imagine the air that surrounds you slowly eroding, say, your cartilage—but because these sea snails are a major food source for other important species like salmon, herring, and mackerel. Their disappearance would radically transform the coastal biome.

    Acidification primarily effects the snails' outer shell layer, and is especially dangerous to juveniles, which are born with very tiny shells. The outer shell, which is comprised of "a more soluble form, they are just dissolved away. In that sense, shells are getting more thin," Bednarsek said. "It is just a few micron in juveniles. If you dissolve that, the whole shell can just disappear in two months time."

    This means they have to use precious energy to try to build shells with less soluble materials, while the absence of a shell restricts mobility and leave them vulnerable to infection. So is this an existential threat to a highly prevalent species?

    "Yes, basically," Bednarsek said.

    "By 2100, 50 percent of the oceans would no longer be viable for pteropods," Dr. Richard Freely, the study's co-author, told me, if we continue emitting carbon pollution apace. And that's exactly what's expected to happen.

    "Estimates of future carbon dioxide levels, based on business as usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150 percent more acidic, resulting in a pH that the oceans haven’t experienced for more than 20 million years," NOAA estimates.

    In other words, the oceans are on track to become an acidic mess, and plenty of things that lived in them for millions of years may simply no longer be able to. The future, it seems, is a place where sea snails' shells begin dissolving in acid as soon as they're born. And then, eventually, a place without sea snails.

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