What happens to creatures that live in the ocean if seawater becomes more acidic? This fun activity, excerpted from The Big Green Book of the Big Blue Sea (Kids Can Press), is an easy to do, seeing-is-believing demonstration.

Humpty Dumpty Coral

Excess carbon dioxide from burning fossil fuels, is gradually making the oceans more acidic. How might more acidic waters affect coral reefs? See for yourself.

You Will Need

an egg

500 ml (2 c.) white vinegar

a large glass container (to hold the vinegar)

plastic wrap

1.     Break the egg neatly in half. Reserve the egg white and yolk for another purpose (like breakfast!).

2.     Measure the vinegar into your container. Place the two halves of the eggshell in the vinegar. Cover the container with plastic wrap.

3.     Watch what happens when you place the shells in the vinegar. Do you see bubbles forming around the shells?

4.     Leave the container in an area where it won’t be disturbed. Then check on your eggshells three days later. Where did they go?

What’s Going On?

Eggshells are made out of calcium carbonate, the same mineral that coral polyps use to make their shells. Vinegar — an acid — reacts with the calcium carbonate, removing the carbon from the shell. The carbon combines with oxygen to make the gas carbon dioxide. Those are the bubbles you saw rising from the egg.

With no carbon left in the shell, the shell literally dissolves and disappears. What you see floating in the vinegar is just the soft membrane that lines the eggshell. It is similar to the soft bodies of the corals. Like the egg membranes, the coral bodies would float off without their calyces. They’d be totally vulnerable to predators.

What’s Happening Now?

Despite their tiny size, corals build structures that are so gigantic they can even be seen from space! To do so, they need just the right conditions. They need water that is the right temperature, clarity and acidity. They need to remain undisturbed. And they need the right kind of base to lay the foundation for the reef.

Today, reefs are at risk all over the world. Global warming, ocean acidification, pollution and habitat destruction are all taking their toll. So people are lending corals a helping hand. The Reef Ball Foundation, for example, is a non-profit organization dedicated to building artificial reefs.

The foundation makes ball-shaped, concrete structures. They lower them in waters where an existing reef has been damaged. Teams of scientists hand “plant” about 500 corals per day onto each structure. The scientists then monitor the growth and health of the corals until the reefs re-establish themselves. The process can take 3–5 years. Since their founding in 1993, the Reef Ball Foundation has helped rebuild coral reefs in more than 70 countries.

 

The Big Green Book of the Big Blue Sea has been longlisted for the Information Book Award from the Vancouver Children's Roundtable.