Here it attaches itself to a hard surface and becomes a coral polyp. At this stage the coral polyp begins to reproduce asexually in a process called budding . The coral polyp divides making an exact genetic copy of itself which it remains fused to. As new polyps are built and added a coral colony develops. Extraordinarily, in many parts of the world, mass coral spawning events occur on the same night once a year.
Coral reefs are complex, multi-story structures with holes and crevices shared by various creatures.
If a coral reef can be thought of as a metropolis of the sea, then a coral colony can be thought of as an apartment building with many different rooms and hallways that house different marine species. Not all coral species build reefs. The actual architects of coral reefs are hard or stony corals, which are referred to as hermatypic or reef-building corals. As the polyps of stony corals grow, they produce limestone for their skeletons. When they die, their skeletons are left behind and are used as foundations for new polyps, which build new skeletons over the old ones.