Once a year, on cues from the lunar cycle and the water temperature, entire colonies of coral reefs simultaneously release their tiny eggs and sperm, called gametes, into the ocean. The phenomenon brings to mind an underwater blizzard with billions of colorful flakes cascading in white, yellow, red, and orange.
In ways that scientists still do not fully understand, mature corals release their gametes all at the same time. This synchrony is crucial, because the gametes of most coral species are viable for only a few hours. The “blizzard” makes it more likely that fertilization will occur.
The gametes, full of fatty substances called lipids, rise slowly to the ocean surface, where the process of fertilization begins.
When a coral egg and sperm join together as an embryo, they develop into a coral larva, called a planula. Planulae float in the ocean, some for days and some for weeks, before dropping to the ocean floor. Then, depending on seafloor conditions, the planulae may attach to the substrate and grow into a new coral colony at the slow rate of about .4 inches a year.