Coral reefs may look like an underwater garden, but coral is NOT a plant or a rock. Coral reefs are made by millions of tiny animals called polyps. A coral polyp is a soft-bodied animal related to sea anemones. The polyp has a gut and a mouth at one end that is surrounded by tentacles. These tentacles have stinging cells on them. The polyp spreads its tentacles to catch plankton in the water. It stings the food and then pushes the plankton into its mouth with its tentacles. Some coral polyps also have algae, called zooxanthellas, living inside them. The algae provide food for the polyp. In return, the polyp gives the algae a place to live.

Most coral polyps live in colonies, each animal connected to the others by a layer of tissue. There are two main kinds of corals, soft coral and hard coral. Soft coral polyps have fl exible skeletons that bend easily. Soft corals include sea fans and sea whips. Hard or stony corals are the reef builders. Hard corals secrete a hard, protective outer skeleton made of calcium carbonate, the same material as classroom chalk. The polyp actually sits atop its skeleton. The surface of the skeleton has cups or grooves into which the polyp can retract. As the polyp grows, the skeleton builds up beneath it. When a polyp dies, it leaves behind its skeleton. New polyps will attach and grow on top of these old skeletons. This is how a coral reef is formed.

There are more than 2500 different types of coral. Coral comes in a variety of shapes. Some hard corals look like tree branches or the antlers of a deer. Brain coral looks like a human brain. Soft corals look more like plants or trees. Some are shaped like fans or feathers. Coral is every color of the rainbow, from brilliant reds and vibrant pinks to deep purples and blues. Much of the color in hard corals comes from the algae living inside them.

Coral reefs provide a home for almost a quarter of the animals in the ocean. They are often called the “rainforests” of the sea because of their diversity of marine life. These important ecosystems are facing extinction from a variety of sources. Fragile reefs can be permanently damaged by ships’ anchors, fi shing practices such as dynamite blasting, and even handling by divers. Pollution has sickened the coral and other animals. Runoff from farms and construction is smothering the coral, causing the algae to die. Warming temperatures in the ocean have also affected the delicate balance between the algae and their host coral. Our carelessness will destroy reefs that have taken centuries to grow. It’s time for humans to take care of the planet that supports and sustains us.