If coral reefs disappeared, essential food, shelter and spawning grounds for fish and other marine organisms would cease to exist, and biodiversity would greatly suffer as a consequence. Marine food-webs would be altered, and many economically important species would disappear.
Since it is also a shelter for fish, do all fish sleep or live in the corals?
Most fish rest. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.