Shell shocked: emerging impacts of our acidifying seas

Pry open your first oyster shell, and the vision that greets you isn’t that appetizing. The grey, shiny glob inside looks cold and slimy. But people the world over are obsessed with eating this shelled delicacy.

“The most popular way to eat them in Australia is raw,” says Elliot Scanes. He’s a marine biologist at the University of Sydney in Australia. While oysters may be slimy and “have the texture of a booger,” he notes, the flavor is a winner with a lot of people. Oysters, he says, “taste like salty sushi.” And there’s big business in these ocean boogers.

In the U.S. Pacific Northwest, oysters bring in $111 million per year. In Australia, where Scanes is a marine biologist at the University of Sydney, it’s $26 million.

But those millions — and the oysters that bring them in — are in danger. In the Pacific Northwest, baby oysters have died off by the billions. Their tiny shells dissolved before they were fully formed. In Australia, Scanes finds there are more female and fewer male Sydney rock oysters — which could affect how many oysters fill the plates of Australian diners.

The cause is ocean acidification. Through their industrial activities and the burning of fossil fuels, people have been pumping more and more greenhouse gases, such as carbon dioxide, or CO2, into the air. The ocean will absorb about one-fourth of that gas. There, it will react with water in ways that make the ocean slightly more acidic.

People might never notice the change when going for a swim, but to organisms that call the sea home, acidification is a source of stress. It puts many of the seafoods we love to eat — such as oysters — at risk. And the only way to stop it is to stop the release of CO2 into the air.

The ocean: So basic
Today’s ocean is slightly basic, or alkaline. Scientists use the 14-point pH scale to classify substances from very acid to very alkaline. Pure water is a perfectly neutral 7. Battery acid falls around 1. Soapy water is about 12.

Water in the ocean contains salt (sodium chloride) and other chemicals such as calcium and boron. Water molecules themselves are always morphing. The H2O breaks into negatively charged hydroxide ions (oxygen and hydrogen) and positively charged hydrogen ions. Those hydrogen ions are the very definition of an acid. (An acid is any substance that releases hydrogen ions.) A lot of extra hydrogen atoms makes a substance acidic.

Some of those ions react with the other chemicals in water. If hydrogen ions outnumber hydroxide ions, water is somewhat acidic. If hydroxide ions outnumber hydrogen ions, it’s more basic. Ocean water is slightly basic, with a pH around 8.2.

Or at least, that’s what it used to be.

Around one-fourth of humanity’s emissions of CO2 are being absorbed by the world’s oceans. There, this gas reacts with water molecules and carbonate ions (one carbon and three oxygen atoms). The result is a chemical called bicarbonate — and a bunch of leftover hydrogen ions. Those hydrogen ions add to the hydrogen ions already present, making the seawater more acidic.

Bethany Brookshire, Science News for Students, 28 February 2019. Article.

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