Coral ReefsCoral reefs grow in photic zones of tropical seas, where sufficient light penetrates into the water. In order to survive, the reef must be in an area with mild wave action. Mild wave action is not so strong that it tears the reef. But it is strong enough to stir the water and deliver food and oxygen.Coral reefs are made of millions of skeletons from small animals called polyps. After polyps die, waves and fish break down their skeletons. Then the fragments settle into the reef and cause it to grow. Algae feed on the skeletons andconvertthe material to limestone. The limestone is deposited over the reef and forms a protective crust. These algae grow best in clear, shallow water.Most of the world's reefs are located in the tropical waters of the Pacific or Indian Oceans. There are few reefs on the western coasts of North and South America and Africa. This is due to the strong cold coastal currents in these areas.Coral reefs support a vast array of biodiversity. They create a habitat for many species of fish and plant life to thrive. Without the reefs, many of these species would face extinction.Currently there are several threats to the reefs of the world. Much pollution that runs off from factories and farms kills coral reef life. The water quality in these areas often becomes poisonous, killing off the coral reefs and the creatures that live on and aroundthem.Another threat to coral reefs is over-fishing and destructive fishing by humans. Many fishermen who trap exotic fish for pet shops use cyanide gas to stun fish. This process decreases the lifespan of the captured fish and poisons the reef. Dynamite fishing is another method that damages reef ecosystems. It kills the corals which are the habitat for a healthy reef. Many conservation groups are actively trying to protect the coral reefs of the world.According to paragraph 6, which of the following is NOT true about coral reefs …