Corals get their energy in two different ways. This fun game will explain both, and help you to understand how a static coral can feed on detritus in the water.

Activity steps

1. Put on a glove.
2. Mark the gloved back of the hand with green dots using stickers or a green marker pen. These dots represent the algae (zooxanthellae) within the coral polyp.
3. Stick squares of double-sided sticky tape around each gloved finger. The stickiness represents the stinging cells on each tentacle / finger.
4. Create a sleeve out of the paper bag or paper that fits your hand. This represents the corallite or limestone cup that the polyp lives in.
5. The gloved hands will be closed into a fist during the day. This protects the tentacles from predators, and the algae (zooxanthellae) will still be exposed to sunlight, which provides the coral with between 70% and 90% of its energy via photosynthesis.
6. At night, the polyps open up and feed on zooplankton. If you are in a group, sitting next to someone else, you could represent a small coral colony.
7. Close your eyes and get ready to try to catch zooplankton with your fingers. One of your team members can scatter cotton wool (representing zooplankton) over each coral colony.
8. Open your eyes to see how much zooplankton you have caught.

• Surgical or other latex or plastic glove
• Double-sided tape
• Green markers or green stickers
• Paper bag or 15cm x 30cm strip of construction / sugar paper
• Cotton wool balls

How corals feed

Corals get their energy both from photosynthesis and through catching zooplankton with their tentacles.

Review the activity using these prompt questions

Can you describe the two methods that the coral polyp uses to get energy?

During the day, the coral polyp receives sugars from the zooxanthellae that live inside them. The zooxanthellae create sugars through photosynthesis. At night, the coral polyp also catches small animals, eggs and larvae (zooplankton) using its tentacles.

Do coral polyps eat the zooxanthellae?

No, the coral polyps do not eat the zooxanthellae. This is an example of a symbiotic relationship. The zooxanthellae receive nutrients and protection from the coral polyp and in return share the sugars it creates through photosynthesis.

Why do you think coral polyps might need zooxanthellae?

This is a tricky question and the topic also puzzled Charles Darwin when he visited the coral reef. The tropical waters where coral reefs are found are nutrient-poor. This is one of the reasons they are so clear. Darwin wondered how there was such an abundance of life with so few nutrients in the water. The answer is the relationship between coral polyps and zooxanthellae.

What would it be like to have a plant living inside you?

We will leave this one up to the imagination of your students, but it is just another example of the amazing diversity of life on this planet.