What environment do coral reefs need to survive?

Coral reefs are very sensitive to changes in sea level and temperature.  They need a temperature range of 25-29 C (77-84 F) to grow and they tend to live in waters with lots of movement or strong currents.  These waters can carry nutrients through the reef system.  While the reef systems grow in shallow water, the water cannot be shallow enough so that the tides will expose the reef at low tide or put it more than 50 m (164 feet) below the surface at high tide.