Coral polyps are minute marine animals that live in colonies each attached to the other by living tissues. Each coral polyp secretes around itself a protective limestone cup that is linked to other cups. Linked together this assembly of cups gives rise to a tremendous number of different shapes and sizes. As most corals are immobile they reproduce sexually by releasing eggs and sperms in the water at given periods of the year. This is known as spawning.
Corals spawn at about the same time during the night a couple of days after the full moon.
In some regions spawning occurs in October or November and in other regions that happens in March or April. For most corals, fertilisation is external. A larva called a planula results from this fertilisation. The next generation of coral reefs originates from this free swimming larva called a planula. When it settles on the sea bed it reproduces asexually by budding and produces up to four polyps each of which, in turn, reproduces asexually giving rise to still other polyps, each secreting its protective cup of lime connected to the cups of neighbouring polyps.