1 The Great Barrier Reef on Australia's northeastern coast is the largest structure made by animals in the world. It can be seen from space! It is made up of more than three thousand reefs and over seven hundred islands. It is a World Heritage area that covers more than 300,000 square kilometers, and it is one of the wonders of the natural world.
2 A reef is made of coral polyps, tiny animals that join together to form large communities. They feed on microscopic algae in the water. Each of the creatures produces a substance called calcium carbonate which forms a hard casing around the animal, creating the material we recognize as coral. When the polyps link together, they make forests of colored coral in shapes and structures.
3 Coral needs lots of sunlight to grow and it develops best in shallow, warm, salty water. Some grow really quickly, and others take hundreds of years to mature. When the coral is alive, it is colorful, and when it is dead, it is white. If the temperature in the water rises too high, coral can suffer from bleaching, and many corals die. Another big threat to the Great Barrier Reef is the Crown of Thorns starfish, which feeds on the coral and destroys it.
