Reef growth involves several processes. (
a
) The framework is made whenreef-building corals settle and grow on some hard surface, usually a preexisting reef. (
b
) The spacesin this framework are partially filled in by coarse carbonate sediments. (
c
) When the sediments areglued together by encrusting organisms, new reef “rock” is formed and the reef has grown. On areal reef all three steps go on at the same time. Reefs are not actually completely solid as depictedhere but are porous, with many holes and crevices that serve as home to a host of organisms