The coral animal starts life as a small planktonic larva which,when it comes to rest on a suitable substrate, metamorphoses into a polyp—a tiny animal rather like a sea-anemone. This polyp begins dividing asexually, producing countless genetically identical individuals, or clones of itself, which over time grow into large conglomerations. Coral polyps secrete a limestone external skeleton. As they die, new polyps form on their skeletal remains, resulting in the steady expansion of the coral reef. By way of sustenance, coral polyps feed off plankton and other tiny sea creatures which they ensnare in their hydra-like tentacles. Small photosynthetic organisms—golden-brown algae—live within the ‘skin’ of the coral polyp, absorbing waste products released by the polyp while using the sun’s energy to convert phosphates and nitrates into protein, and carbon dioxide into oxygen which is used by the coral polyp for its respiration. Coral polyps reach sexual maturity after about three years, releasing their gametes simultaneously into the surrounding seas in order to ensure the maximum opportunity for eggs to meet with sperm, This mass reproduction typically occurs at night usually a few days after a full moon.