This is precisely what a coral animal needs to grow. The more sunlight the better. Reef building corals, like most animals, have a calcium skeleton. Fast growing corals may expand one inch per year although most are much slower. During the day, when the photosynthetic algae are most productive, corals grow approximately 14 times faster than at night.
Clouds can reduce growth by half.
Eventually, this calcium, which over time may be hundreds of feet thick, becomes the actual reef structure. The coral animal essentially becomes a living veneer over it's own dead body. The calcium skeleton provides an excellent fossil record and core samples yield fascinating geological insights. Corals have survived for over 500 million years, so they must be doing something right. Changes in the elevation of the sea due to passing ice ages and tectonic land movements are accurately reflected by ancestral reefs, now stranded high above and below our modern-day sea level.