Once a year, an entire reef releases its eggs on the same single night
Dozens of coral species on the Great Barrier Reef synchronise their spawning to a handful of nights a year, cued by water temperature, day length and the phase of the moon, usually a few nights after a full moon in spring. Millions of colonies release eggs and sperm within the same hour, briefly turning the sea surface pink and giving fertilised larvae a window to disperse before predators arrive.