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Why Scientists Think Some Shellfish Could Be Extinct in 50 Years

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In the past 250 years, the ocean's global pH level—that is, it's level of acidity/basicity in all the world's oceans—has dropped from 8.2 to 8.1.

This may not seem like a big deal to you or me or the average seafood consumer. But if you're a scientist, or shellfish farmer or fisherman, or a shellfish, it's a big deal indeed.

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Photo by James Ransom

The ocean is growing more acidic. According to Woods Hole Oceanographic Institute, which has led a number of research initiatives on ocean acidification, "this change [from 8.2 to 8.1] represents a 26 percent increase in acidity over roughly 250 years, a rate that is 100 times faster than anything the ocean and its inhabitants have experienced in tens of millions of years." For oysters, mussels, clams, and other shellfish (and coral reefs), this reflects a significant change in their environment, and their shells are, as a result, getting thinner and more brittle.

This isn't something we'll likely notice as consumers (not yet, anyway, though Gizmodo, where we first read about the issue, warns that extinction for some shellfish could be nigh). But many scientists (and, increasingly, farmers and fishermen) are, and are beginning to ask questions and make plans for the future: How will this affect shellfish larvae? How will it affect adult crops? How will it affect fishermen's ability to harvest shellfish and deliver them to consumers?

But first things first: What exactly is ocean acidification? And why is it such a big deal?

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"It's a really complex problem," Chris Sherman, president of Island Creek Oysters (whose oysters we sell in our Shop) and of the Massachusetts Aquaculture Association, told me. Acidification is affecting the oyster industry, he said, though they haven't much seen its effects in Duxbury, Massachusetts, where their oyster farm is—it is affecting shellfish in the Pacific Ocean more quickly because the continental shelf, where many shellfish grow, is closer to the shore, and is thus more immediately susceptible to localized carbon dioxide pollution. (The International Business Times even said that the end for Pacific mussels is nigh.)

"The poster child of ocean acidification is anthropogenic," Chris said—human-caused, and specifically carbon dioxide from factory or fertilizer runoff. What's causing this current increase in acidification are traces of carbon emissions from 150 years ago, from the beginning of the Industrial Revolution, making their way via ocean currents from deeper waters to ones closer to the surface and to the shore, the continental shelf—which is a very productive place for ocean life. It's where the shellfish we eat grow happily, with easy access to algae (which they eat).

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The more carbon dioxide in water, the lower the pH level and the higher the level of acidity. And that acid eats away at the calcium carbonate shells of mussels, oysters, and clams, making their shells thinner and more brittle. This increases the likelihood of what Chris called a "mortality incident," a mass shellfish death due to their being more susceptible to viruses, parasites, natural disasters (like hurricanes), or manmade disasters (like oil spills)—all issues that oyster and other shellfish farmers have to navigate daily, but ones that become more deadly when the shellfish are more fragile.

Chris is aware of the dangers of acidification, and is sketching out plans for how to keep Island Creek's oysters healthy in the event that the pH levels do decrease significantly, but he's not too concerned yet. People in the industry are definitely talking about it, he told me, and he's heard of a few farms already taking precautions for a large-scale pH shift. But scientists are the ones most vocal about the issue for now: "There are people who are totally unconcerned and seeing shellfish evolve to be tolerant of lower pH. And then there are the Chicken Littles of the world, who think these animals might be extinct in 50 to 60 years," he told me. "It's hard to say who's right."

Tags: shellfish, ocean acidification