Coral Reproduction

Corals exhibit sexual and asexual reproduction. The coral colony expands in size by budding. Budding may be intratentacular, in which the new bud forms from the oral discs of the old polyp, as in Diploria (brain corals), or extratentacular in which the new polyp forms from the base of the old polyp, as in Montastraea cavernosa (boulder coral).

A common type of asexual reproduction in corals is by fragmentation. After a storm strong enough to break off pieces of coral, any pieces that land on a suitable substrate may begin to grow and produce a new colony. This type of reproduction is common in branching corals like Acropora cervicornis and A. Palmata. A large patch of these species may be all of one genotype, or clones of the same colony broken up. A positive correlation has been found between fragment size and survival: small pieces rarely survive.

Many coral species mass spawn. Within a 2-hour period (and often a lot shorter- a few minutes) all the coral from one or several species release their eggs and sperm at the same time. This occurs in species of Montastraea (boulder coral), and in other genera such as Montipora, Platygra, Favia and Favites (smaller coral species). In some Montastraea and Acropora (branching corals) species, the eggs and sperm are released in a sack. The sack is larger then the egg and sperm would be on their own, and are thus less likely to be eaten by predators, including other filter feeders or corals. They float to the surface where they separate, and there fertilization takes place. The zygote (fertilized egg) develops into a larvae called a planula, which attaches itself to a suitable substrate (rocky bottom) and grows into a new coral colony.

Intra species mass spawning is common, but raises the possibility of hybridisation (cross breeding) by congeneric species. Usually these hybrids won't survive, but Acropora prolifora (Fused Staghorn coral) is a hybrid of A. palmata (Elkhorn) and A.cervicornis (Staghorn) coral which does.

After a mass spawning event, the water feels greasy on the surface, and often has a sickly sweet smell.

Some species of coral brood their larvae. The sperm fertilizes the egg before both are released from the coral. The larvae float to the top, then sink, settle, and become another colony. Some species of Acropora release brooded larvae.