CORAL REEFS A quarter of all animals that live in the sea live in coral reefs. They are the rainforests of the sea. However, we have lost 27 percent of our coral reefs in the past 50 years according to the Coral Reef Alliance. Why are they dying? sometimes directly, sometimes indirectly-is the problem. Fishermen use explosives and poison to kill fish. They kill the fish but they also kill the coral. Ocean temperatures have increased due to climate change. Coral needs water to be at exactly the right temperature. If the water is too hot, the coral will die. So man's activities are indirectly killing the coral reefs.