1. Coral animals build reefs by dying and their skeletons pressing together over time. Reefs grow on top of older reefs. Coral can only live in warm, shallow, clear salt water. 2. Volcanic islands surrounded by coral reefs can sink over time, leaving the reef exposed as a ring-shaped atoll surrounded by a shallow lagoon. 3. Typhoons are large, damaging storms that occur in the Pacific tropics during the summer and can destroy small coral islands.