The coral is made up of communities of small polyps that build, at the base of their own soft body, a calcium carbonate skeleton with a protective and supporting function. The polyps grow next to each other, so that the limestone secretions merge with each other and stratify, forming coral reefs, such as the Australian one, the largest in the world, covering an area of over 80, 000 square miles . With the death of the organism, the skeleton is colonized by other polyps.
At the mercy of the waves. In the tropical seas the polyps multiply dividing many times, thus increasing the size of the colony. In adverse situations (for example of overpopulation) the polyps release into the sea millions of spermatozoa and eggs in sync at high tide. It happens to one egg out of ten million to be fertilized: a larva originates that, carried by the currents, goes to fix itself on a rock where it turns into an octopus, and begins to divide, giving rise to a new colony.