The reef flat, like that on fringingreefs, is a shallow, nearly flat platform.Sand and coral rubble patches are inter-spersed with seagrass or seaweed beds,soft corals, and patches of dense coralcover. Waves and currents may pile upsand to form small sand islands called
sand cays
or, in the United States,
keys.
The richest coral growth is usually at the outer reef crest. There may be a