Coral reefs are arguably the world's most beautiful habitats. Coral reefs have been called the rainforests of the oceans, because of the rich diversity of life they support. Scientists have not yet finished counting the thousands of different species of plants and animals that use or live in the coral reef. There are three types of coral reefs: fringing reefs, barrier reefs, and atolls. Fringing reefs are located close to shore, separated from land by only shallow water. Barrier reefs lie farther offshore, separated from land by lagoons more than ten meters deep. Atolls, on the other hand, are formed far offshore and they make a ring-shaped reef that close a circular lagoon. .
Coral reefs are the largest biological structures on the planet, with the largest being the Great Barrier Reef covering over 2000 kilometers along the east coast of Australia. The reef is said to be 500,000 to 2,500,000 years old and is said to be visible from the moon. There is only one problem with this beautiful structure and that is the carelessness of man. Silt from deforested lands and pollution from crowded coastlines chokes them, and overuse by coal miners, fisheries, and even tourists deplete and destroy coral reefs. There are many more factors which add to the destruction of the coral reefs, which if not stopped it will destroy all coral reefs. Corals are animals, not plants; sunlight is the key to their survival. They need it to power the millions of microscopic algae, called zooxanthellae, which live in their tissues. The algae provide the corals with food and oxygen in return for raw materials and a secure place to live. This teamwork is what allows the reef to survive in nutrient-poor tropical seas. This relationship is sensitive to such changes in the environment as cloudy waters or extreme temperatures. The stress on the corals can cause them to expel their algae, a phenomenon known as bleaching. With the algae gone, the coral skeleton is visible and eventually it dies.