Ever wonder how stony corals grow to form massive reef structures? The answer is, slowly (1-10 millimeters a year)! Each coral polyp sits in a stony cup, or calyx, the floor of which is called the basal plate. Periodically, the polyp lifts off its base and secretes a new basal plate above the old one, creating a small chamber in the skeleton. Calcium carbonate is then deposited into this chamber, elevating the coral. Learn more here: https://oceanservice.noaa.gov/education/tutorial_corals/coral0