Coral reef (Andreas März / CC BY)
Coral reefs are typically created from calcium carbonate secreted by stony corals. They form highly diverse ecosystems. Coral reefs cover less than 0.1 percent of the world’s ocean floor. However, they provide a habitat for 25 percent of all marine species. Typically, a water temperature of 26–27 degrees Celsius (79–81 degrees Fahrenheit) is required for stony corals to grow (and reefs to build up).