You’ve probably heard about global climate change, but there’s another problem that poses an even greater threat to coral reefs and other shell-building ocean animals. That threat is called ocean acidification, which stems from the same problem of too much carbon dioxide (CO2) that leads to global climate change. CO2 levels are building up not just in Earth’s atmosphere, but also in the oceans. As the oceans absorb more CO2, they become more acidic. Marine snails, clams, crabs, sea stars, and many other small ocean animals use calcium carbonate, which is normally abundant in seawater, to build their skeletons or shells. Reef-building corals also use calcium carbonate to construct their skeletons, which accumulate over the years to form coral reefs. Yet, an increase in acidity (from more CO2 in the water) dissolves calcium carbonate shells and skeletons and even leads to a decrease in calcium carbonate levels in seawater, preventing newly developing animals from forming their shells or skeletons.
One great way to demonstrate ocean acidification has on shell-building animals is through the following simple experiment. You’ll need the following items:
- 2 small pieces of teacher’s chalk
- 2 clear, plastic, drink cups
- 1 cup drinking water
- 1 cup clear, non-diet soda or white vinegar
- scale
Provide students with an explanation about ocean acidification and ask the students to guess which liquid they think will dissolve the chalk, which is made of calcium carbonate. Place drinking water in one cup and the acid (soda or vinegar) in the other cup and label both cups. Weigh each piece of chalk, then place each in a cup. Watch what happens (bubbles or fizzing indicates that the chalk is dissolving.) After 30 minutes remove chalk. Does it look different. Let chalk dry and then weigh each piece again. Does either piece weigh less than before?
Discuss what happened with the students? Teacher’s chalk is made of calcium carbonate — the same material that coral and many other ocean animals use to build their skeletons or shells. Tap water is not acidic and does not dissolve calcium carbonate; this represents the normal state of seawater. Vinegar, and soda are both acids, which dissolve calcium carbonate. If the oceans continue to become more acidic, then coral reefs and other shell-building animals could disappear. Without changes from us, more than a million ocean animals, including ones that rely on coral reefs and shelled animals for food and shelter, could become endangered because of ocean acidification. Have students brainstorm on what simple things they can do, both at home and at school, to help reduce the amount of carbon dioxide in the Earth’s atmosphere.
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