On its gently sloping shelf off to the northwest, the black lines on the ocean floor are 200 meters, about 660 feet, depth of water. To the west is deep ocean. The red bands are reef terraces now drowned beneath the sea. The graph in the lower left shows ages of these reef terraces in centuries. The sixth one is not indicated.
Reefs grow only near sea level, and they grow away from shore into the waves.
These old, older, and oldest reef terraces are wonderful. They are the natural reactions of the reef animals and plants to two different truly earth-scale processes. Sea level went down hundreds of feet as glacier ice grew on land during ice-age expansion. As ice melted in the waning ice age time, sea level went up, but the island continued to sink, so the reef was lowered into the dark and died. When the next ice age started, a new reef thrived closer to the present shore, It is a happy coincidence that sea level went down at about the same rate as the rock sank, and another happy coincidence that it happened so many times and datable times that we can understand it .