Coloring Book, Coral

An Introduction to Coral

I’ve decided to add a section to my coloring book about coral. This decision came about while I was talking to my mom (who is going to be joining us on the upcoming snorkeling trip) and telling her about some exciting new study on coral I had read. She stopped me to ask, “So why is coral in trouble right now? I know that it is, but I’m not really sure why.” As I began to explain what coral bleaching is, I quickly realized I needed to pause and first cover some coral basics so we could have a common understanding to build on. This section of the coloring book is intended to help give my neice and the rest of my family (and anyone else who’s interested) some common knowledge about coral so we can talk about all the problems facing coral right now.

You can read about this project in the post “A Fish Journal for a six-year-old” and you can see all the posts for this project using the tag “Fish Coloring Book“.

Learn About Coral

Coral is an amazing marine animal that lives in warm, calm, clear tropical oceans.  Although some coral can look a bit like a plant, it is actually an animal. 
In fact, most coral you see are actually a single colony made up of millions of tiny individual animals called coral polyps. The polyps can be very big or very, very small. Polyps in coral colonies join together to form some really amazing structures and shapes.

Coral Polyps and Coral Colonies

Most of these shapes have evolved over millions of years to help maximize the surface area for capturing sunlight. This helps ensure that they always have all the food they need to live.
When you see a coral, you are most likely looking at a colony or group of coral polyps. Most coral live in colonies made up of millions of polyps. Only a few types of coral live as a single, individual organism.


Coral polyps have a very special symbiotic relationship with an organism that is often called zooxanthellae (zo-zan-THEL-ee).  A symbiotic relationship is one where two organisms rely on each other to survive – they both provide something the other one needs.  Zooxanthellae are very, very tiny single-celled organisms that can only be seen with a microscope. They live inside the actual tissue of the coral polyp. 

Zooxanthellae can photosynthesize like a plant – which means they use light from the sun to create food. The coral provides a safe home for the Zooxanthellae as well as some important nutrients they can’t make through photosynthesis. In exchange, the Zooxanthellae share the food they make from sunlight with the coral. In fact, coral gets about 90% of its food from the Zooxanthellae that live in it. 

During the day, the Zooxanthellae are hard at work using sunlight to produce food. At night, all the coral polyps extend their tentacles and use them to catch little bits of food called plankton.

Coral Anatomy

Coral polyps have a very simple anatomy. Anatomy is the shape and structure of an organism’s body. 

Coral Polyps have a tube-shaped body with a big open space in the middle where they digest their food. This area is called a gastrovascular cavity and it is basically their stomach. 

The opening at the top is where food enters and waste exists. This opening is both their mouth and their anus which may not sound very nice, but their waste is very different from ours.  At the top, there are tentacles that have special stinging cells for catching prey.