Once a year, a few nights after a particular full moon, hundreds of coral species along 2,000 kilometres of reef release their eggs within an hour of each other.

Corals carry light-sensitive proteins called cryptochromes that respond to moonlight specifically, and the moonlight sets the night while water temperature sets the month. Spawning together in one enormous slick is a numbers game against predators. It is the largest synchronised reproductive event on Earth, and the Moon is the clock.