School › Coral reefs › Ages 6–7
The busy coral reef
Corals look like rocks or plants, but they are animals! Find out how tiny corals build huge reefs, who lives there, and what vinegar does to a shell.
Read
A coral may look like a rock or a plant, but it is an animal. It cannot make its own food the way plants do.[1]
Each coral animal is called a polyp. Most polyps are tiny, no thicker than a small coin. They catch food with little arms called tentacles.[1][6]
Each polyp builds a hard skeleton of stone around itself. Millions of polyps, over a very long time, build a whole reef.[1][6]
Tiny plant-like helpers called algae live inside the coral. They use sunlight to make food and share it with the coral. They also give the coral its colours.[2]
Reefs are home to lots and lots of sea animals, like fish and lobsters. Reefs also protect beaches from big waves.[4]
If the sea gets too warm, the coral pushes its helpers out and turns white. This is called bleaching. The coral is not dead yet, and it can get better if the water cools down.[3]
Try it: What does vinegar do to a shell?
You need
- Two clear cups or jars
- White vinegar
- Water
- Two clean seashells (clam or mussel shells)
- Labels and a pen
Safety
An adult pours the vinegar. Keep vinegar away from eyes; if it splashes, rinse with water. Do not drink anything. Wash hands afterwards.
What to do
- Label one cup 'water' and one cup 'vinegar'.
- Pour water into the first cup and vinegar into the second cup.
- Guess: will anything happen to the shells?
- Put one shell in each cup. Look closely at the shell in the vinegar. Do you see tiny bubbles?
- Leave the cups and look again the next day. Feel the shells (with clean hands). Are they the same?
What happens, and why?
Shells and coral skeletons are made of the same kind of stone (calcium carbonate). Sour liquids like vinegar slowly eat away at it, so the shell in vinegar makes bubbles and gets weaker. The sea is slowly getting a tiny bit more sour, which makes it harder for corals to build their skeletons.[7][6]
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Other ages: Ages 10–11 · Ages 15–16