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This animation demonstrates how stony corals grow vertically. In the first frame, we see a coral polyp resting on its base, which is called the basal plate. In the next frame we see the polyp’s tissues begin to lift up off the basal plate, leaving an empty space beneath it (shown by dashed lines). In the next frame, the polyp rises even higher, expanding the space between it and the basal plate. In the final frame, the polyp has created a new basal plate to rest on, leaving an empty space between it and the old basal plate. Using this method, a coral polyp can grow anywhere from 1 to 10 millimeters per year, depending on the species and surrounding environmental conditions. Figure credit: NOAA
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