Coral Field Guide

Hard corals reproduce both asexually and sexually. Asexual reproduction may take the form of budding or fragmentation. Budding is the division of one polyp individual into two or more resulting in the formation of a coral colony. Fragmentation refers to the breaking of a coral colony into smaller pieces, sometimes by external force or at times by the colony itself, to produce more colonies.

Sexual reproductive structure (gonads) of corals are located on the mesenteries inside the polyp. Male and female may be found within the same polyp individual, or sexes may be separated in different colonies.

The most common type of reproduction is by broadcasting, i.e. mature eggs and sperms will be released in the water at the same time and fertilization takes place externally. In some species, however, fertilization takes place inside the cavity of the polyp. Fertilized egg will develop into an embryo inside the polyp. Such type of reproductive behaviour is called brooding.  

Larva of hard corals is called planula (planulae for plural). Either releasing from brooding or developed from external fertilization, planulae will spend a few days (or weeks, depending on the species) in the water column before settling down to a suitable place. Once settled, a planula will develop into a polyp and deposit its first corallite. This will eventually develop into a coral colony by budding.