Each year, divers and snorkelers hover over Keys reefs hoping to witness a fascinating yet fragile reproductive phenomenon that occurs in the middle of the night when corals release millions of gametes in synchronized mass spawnings.
Sparked by the August and September full moons, the rare and wondrous underwater exchange of gametes (eggs and sperm) means the continued survival of coral reefs, including boulder corals such as brain and star corals as well as the protected elkhorn and staghorn species, which are branching corals.
Though the polyp release cannot be guaranteed to happen on any exact date, the 2014 late-summer full moons fall on Aug. 10 and Sept. 8.
During the spawn, the spectacular white excretion enables the eggs and sperm to enter the water in massive quantities over a broad geographic area, maximizing the chances of fertilization and overwhelming predators with more food than they can consume.
When egg and sperm do unite, the newly formed larva, or planula, ascends to the surface to float free in the current. Within a matter of days or even weeks, the planula settles to the bottom to grow into a polyp and eventually form colonies.
What triggers this event remains unclear, though scientific observations indicate a strong connection between the coral spawn and seasonal lunar cycles as well as multiple environmental cues such as water temperature and tidal and 24-hour light cycles.
Cultured corals, the result of ongoing wild transplant efforts by Key Largo's Coral Restoration Foundation, also have been documented as spawning in synch with wild corals.
A number of Keys dive operators offer scheduled coral spawning night dives around the full moores to view the spectacle that has been described as an upside-down underwater snowstorm.