Corals have two modes of reproduction, asexual and sexual. Asexual reproduction occurs in several patterns. In terms of fragmentation, the fragments from broken coral colony are resulted from natural currents or human activities, later, each of them can be developed into a new colony if it’s in the appropriate conditions. In adition, some polyps can be developed and droped off from donor colony when they fully become mature (polyp expulsion) or, in some cases, the improper conditions derived from environmental changes and having more predators, coral polyps or tissues may also droped off from donor colony (polyp bail-out) when donor colony is not healthy and further developed. In some corals such as Pocillopora damicornis, they can produce coral larvae by itself from the unfertilized eggs (partheno-genesis). In sexual reproduction, there are separate sex colony and hermaphroditic colony, which is able to produce both female and male gametes within the same colony, however, relative low number of coral species having only one sex in a colony is found. Seventy-five percents of coral species that release their egg and sperm bundles into the water column for fertilization (external fertilization), are called spawner. The spawners which release their gametes once a year, for example, staghorn corals (Acroporidae). Another fertilization is internal fertilization which is occurred within the coral colony. Afterward, the corals release swimming larvae (planula larvae) into water column called brooder. The quantity of larvae released from internal fertilization is less than which from external fertilization, but the brooders are usually released every month throughout a year. The duration of planula larvae living in water column before recruiting on the appropriate areas like hard substrates or dead corals, is varied by species. Seasonal spawning period also differently occurs in each species and area depending on several factors which influence the spawning period such as tides, lunar cycles, or seawater temperature. The release of their gametes begins during increased seawater temperature, from spring to summer, after full moon period. However, different global latitude may also cause differences in environmental changes.
Figure Life cycle of coral