Coral reefs in tropical waters form wave barriers. All reefs existing today have been built up during the last 6,000 years. Fringe reefs grow around the shores of continents or islands. Barrier reefs grow several miles offshore. A coral atoll is a broken ring of coral islands with water in the middle. The forward edge of the reefs consist of massive coral. All reef building corals contain symbiotic plant cells.
Coral reefs are found in shallow seas. They are built by tiny animals called polyps. Each polyp builds a small stone cup or a stony skeleton around itself to live in. When the polyp dies, it leaves its cup behind. New polyps build on top and gradually the reef grows. The reef is made up of layers of living coral animals attached to a wall of many millions of dead skeletons. The polyps eat mostly at night when their tiny arms come out of its stony skeleton. The arms catch plankton and feed them into its mouth.
Corals get their colors from the algae that lives inside the coral polyps. Without algae, coral would be white.
Even though coral reefs cover less than .2% of the ocean floor, it is estimated that coral reefs contain approximately 25% of the ocean's species. Almost 5,000 species of reef fish have been identified, and more than 2,500 species of coral, of which almost 1,000 are reef-building hard coral.
Many colorful creatures come out at night. The creatures that come out at night are shrimp, lobsters, crabs, spanish dancers, and core shells that can mostly see at night. The sea creatures are rarely seen at night. Coral reefs are polluted with sewage, oil spills, fertilizers, and pesticides. 75% of all ocean pollution originates on land.
There are a number of things that we are doing to coral reefs that are harming them; over-fishing, dumping chemicals, damaging gears and anchors, and mining them with explosive devices. We drop anchors on them, step on them, and drag diving gear on them. We chop them down for tacky jewelry and coffee table curios. Estimations suggest that two thirds of the world's reefs are dying. Ten percent are degraded beyond recovery. Thirty percent are in critical condition and may die within 10 to 20 years. Reefs need warm, clear, shallow sea water to survive. We need to protect and preserve them.
Coral reefs do a lot for us. They provide shorelines with protection by breaking waves; serve as nurseries for growing fish; supply a protein source in coastal people's diets; give food, shelter, and protection to almost one million marine species; provide jobs through fishing and tourism; and serve as a source of medicine against a variety of illnesses.