Охота и рыбалка

Ocean acidification may ground swimming skates

Author: Bethany Brookshire / Source: Science News for Students

an underwater photo of a little skate — This is a little skate, a fish closely related to sharks and rays. As the oceans get more acidic, little skates may become better walkers.

The more carbon dioxide people pump into Earth’s atmosphere, warming the planet, the more carbon dioxide and heat slip into the oceans.

Новости СМИ2

Warmer and more acidic water is thinning the shells of oysters. But they aren’t the only ocean dwellers facing unwanted home renovations. Anything with a shell is at risk. So, too, may be certain fish. A new study finds that as seawater becomes more acidic, the skeleton of a fish called the little skate stiffens in some places — and gets bendier in others. That could leave this fish better built for walking than swimming.

Burning fossil fuels, such as oil and coal, releases carbon dioxide, or CO₂. In the air, this and other greenhouse gases act like a sweater, trapping heat and raising near-surface temperatures around the globe.

The oceans also absorb CO₂. And there it combines with a molecule known as calcium carbonate. This produces a new molecule, bicarbonate. The reaction leaves calcium and hydrogen atoms stranded. Those free hydrogen atoms act as an acid to lower the ocean’s pH.

This ocean acidification strongly affects organisms that make shells from calcium carbonate, such as oysters and lobsters. Fish have a built-in system for dealing with changes in ocean pH. Vertebrates — animals with backbones — tend to keep their blood’s pH levels under strict control, says Sean Bignami. He’s a marine biologist at Concordia University in Irvine, Calif. These animals, he notes, “can’t survive with a lot of variation [in blood pH].” To prevent their blood pH from changing, fish have to be pH micromanagers.

If a fish’s blood gets too acidic, it extracts a molecule, calcium phosphate, from its food. (This is a calcium atom attached to a phosphate group: a phosphorus atom and four oxygen atoms.) The phosphate is alkaline. And this tends to neutralize the pH of the fish’s blood. Fish are so good at this that they can adjust to acidic waters in only a few hours.