Break-Down of How Corals Grow

Corals use many reproductive strategies, but it now seems that nearly all large, reef building species release millions of gametes once a year, in precisely synchronized mass-spawning rituals. These spectacular displays allow the stationary animals to mix genetically and to disperse offspring over great distances. Such a copious delivery system is also believed to maximize the chances of fertilization, and at the same time overwhelm predators with more food than they can possibly consume. The exact cues triggering the annual phenomenon remain unclear. They are generally believed to be linked to water temperatures as well as the lunar, tidal, and twenty-four hour light cycles.

coral
Releasing Eggs
A few mass-spawners, known as gonochoric species, have separate male and female colonies, and depending on their sex, either release sperm or eggs, which, with luck, will cross fertilize somewhere in the vast water column. Most broadcasters, however, are hermaphrodites (both sexes occurring in each individual coral animal, or polyp). Such polyps once a year package both sperm and eggs into near little pink bundles that are expelled to the caprice of the currents when a biological clock strikes.

coral
Coral Smoking
(Releasing Sperm)
Fertilization, which is possibly aided by sperm attractants, produces planulae larvae that are able to free-swim by day two. Now, in the grasp of tides and currents, the tiny new coral embarks on a grand voyage that can last for months and carry it hundreds of miles from its origin. If the speck of life somehow survives the ever-hungry mouths of plankton-pickers, filter-feeders, and jelly plankton, it will one day mysteriously sense suitable hard substrate below, settle, and begin producing a tiny calcium skeleton – the genesis of a great coral colony that could live for hundreds of years.