The Reproduction Process of Coral

From the class Anthozoa, corals are small sea anemone or polyps. They are typically in colonies of a bunch of identical individuals, inhabiting reefs. Coral that grows in shallow waters are heavily branched, while coral growing in deeper water grows in sheets or plates.

Coral and coral reefs depend on many factors in which to grow such as light intensity, the availability of food, competition for space, temperature of the water, salinity, and of course predators.

The coral have the ability to reproduce both sexually and asexually and the polyps, or coral, may use both reproduction types in its lifetime.

Fragmentation is the most common form of asexual reproduction, especially within the branching species. Due to environmental changes polyps are dislodged from the head of the coral and moved by motion of the waves to a new location, where it will continue to grow. Sometimes a portion of the coral colony will separate and form a new colony elsewhere.

Budding or gemmation, is another form of asexual reproduction. This happens when a section, within a head of a parent coral, separates to form a new polyp. By doing this the polyp is able to reproduce several times and still be able to maintain tissue connections with the colony. The polyp, if chooses to, may also reproduce sexually later on.

Sexual reproduction, for most species, is the most important way to produce offspring. About 25% of coral are hermatypic coral, or stony coral, they are either male or female, while the other 75% are hermaphroditic, can produce both eggs and sperm, together or at different times.

Hermaphroditism is the most common form of sexuality among coral. Both sexes can happen in the same colony, or their can be colonies of individuals of the same sex.

Coral can reproduce sexually two different ways, either by external fertilization or internal fertilization.

External fertilization occurs by releasing eggs and sperm into the water. About 75% of hermatypic coral broadcast spawn into the water this way, to spread colonies over a long distance.

Fertilization occurs best when there is little difference between high and low tides. The eggs have a better chance of getting fertilized, the less the water moves over the reef, typically three to six days after a full moon.

After a few days the fertilized eggs develop into free swimming microscopic larvae called planula. An average size coral colony can produce several thousand planula a year. They are typically pink and elliptical in shape.

The planula goes towards the light to the waters surface where it will grown and drift around for a period of time. It will then swim back down to find a surface it can attach to and establish a new colony.

Once the planula has settled on a surface, it is very vulnerable to different predators from fish to invertebrates. Eventually the planula develops into a coral, and will become a coral head and reproduce asexually.

Coral that fertilize the eggs internally are called brooders. These coral release sperm, but keep the eggs sheltered and protected. This enables the planula to grow larger and form, being ready to settle when they are released.

Development can take several days to weeks, and when released into the water they settle on a surface within hours. Unlike eggs fertilized externally that drift around while developing , brooding coral have a better chance of settling with in the natural reef.

sources:

http://en.wikipedia.org/wiki/Coral

http://www.ecology.su.se/JN/TV/coral_text/c_reproduction.htm

http://www.seaworld.org/infobooks/Coral/reprocr.html