Portion of Enewetak Atoll, Marshall Island. To the right of center is Perry Islet. It is the largest islet visible in the picture and has a length of 2.3 km. The shallow atoll lagoon is to the left of the reef while the deep ocean is to the right. Warm temperature appears to be essential for coral reef growth which is limited to the warmer waters of the tropical and western portions of the world oceans.
Light is also important for coral reef growth.
One will not get the luxuriant type of growth necessary for live reef survival without light. Closeup view of part of a coral tip of Acropora formosa from the lagoon of Enewetak Atoll. The tip is about 25 mm long. I have noted that significant coral growth stops below a depth of 50 m at Enewetak. If light is so essential to reef growth, one may wonder how reefs such as Enewetak extend to a depth of 1405 m in the sea where virtually complete darkness prevails.