Hundreds of species of coral spawn once a year in a mass synchronized event, releasing millions of eggs and countless numbers of sperm into the water a few nights after a full moon.
The timing of spawning varies from species to species and by location. For instance, in Australia’s Great Barrier Reef, more than 100 of the 400-plus species of corals spawn simultaneously over the course of a few nights during spring or early summer.
But how do they coordinate sex on such a massive scale? It turns out that local weather cycles determine the month in which spawning will take place, but the precise night is set by the lunar cycle—which means scientists (and curious tourists) can predict the date of spawning based on the moon.
Shown here is a star coral (Montastraea franksi) releasing egg and sperm bundles. A hungry ruby red brittle star (Ophioderma rubicundum) gathers up the gametes with its arms and creeps back under the coral ledge to consume them in private.