Coral reproduction is surprising to many who think of coral as a form of stone, or as a plant. Coral however, is a living animal. Coral in many forms make up the bulk of the ocean reef landscape. To do so, this organism has to reproduce quickly and efficiently.
Many corals compete for the same space as they share the same criteria for habitat. They are highly temperature specific, and a change in even a few degrees can devastate populations. Because of this there are relatively few places with ideal conditions for these animals.
This leads to some very interesting and dramatic reproductive habits. Sometimes corals flood the reef with thick bursts of sperm and eggs, in order to reproduce as fast as possible. Whatever isn't eaten by waiting ocean dwellers becomes the future of the reef. In many parts of the ocean reefs during favorable lunar tides, hundreds of coral species spawn all at once attracting hungry sea creatures that traveled miles for this extraordinary feast.
To make their offspring, corals have two methods which they employ depending on either the conditions or the species in question.
Asexual reproduction to expand size and turf. The top of the polyp gets longer and eventually breaks off. This creates a being genetically identical to the parent coral, a clone! Most of the time these clones stick near the parent coral, expanding the size of the coral family in the immediate area.
Sexual reproduction that depends heavily on water temperature, day length, and tidal activity. Coral polyps are often hermaphroditic, so fertilization can occur before ejection into the water. In species with separated genders, females shoot clouds of eggs into the sea and male polyps eject sperm, what gets fertilized and isn't eaten survives to make genetically similar (but not identical) offspring.
The coral babies that survive are called planulas. This is the first stage of life as a coral. Hopefully they are carried to a suitable locale. If this is the case, they settle and begin their next phase of life until they too can reproduce.
Coral reefs, because of their steadfast requirements of temperature, light, and salinity are a fragile base for the ocean ecosystem. Much research is still needed concerning reproduction, the loss of habitat, and the effects of rising water temperatures. Aquariums often aid in this research. Waikiki Aquarium in Hawaii is one such place.
At their website, http://www.waquarium.org/coral/index.html , they offer a live web cam. Check back frequently to watch the coral grow! Waikiki aquarium is the leading researcher of coral propagation. Their aquarium grows coral and ships to others so that they don't have to take from the wild and further deplete the reefs. Programs of this sort are essential to keeping reefs healthy for now and for the future.
Windows to the Sea, by John Grant and Ray Jones
Oceans: Life in the Deep, by Beverly MacMillan and John A. Musick