Sexual vs Asexual
Corals can reproduce in two ways - asexually by making clones or sexually by fusion of sperm and egg. Asexual reproduction happens when an adult of any sex produces an exact genetic replica of itself, known as a clone. This can be done in several ways, either by budding off from the body of the main coral, by the production of asexual larvae that are then released into the water column, or (in reef-building species) even by small broken branches falling from the main colony, surviving and growing into new colonies.
Sexual reproduction involves males producing sperm that fertilizes a female’s egg, which then becomes a larvae. This can either happen within the body of the female (brooding) with larvae later released into the water column or fertilization can happen in the water column itself (spawning).
There are advantages and disadvantage to both of these forms of reproduction. Asexual reproduction only produces clones of corals that are already there, so does not shuffle genetic material as in sexual reproduction. Asexual reproduction also only allows for short distance dispersal. On the other hand, sexual reproduction does generate genetic diversity and leads to the production of larvae that can, in some species, travel great distances. However, in fast flowing ocean currents there are downsides to sexual reproduction; the chance of sperm and egg meeting is small and many larvae die before they can settle.