Every month, at the full moon, tourists and students gather on the beach at Koh Phangan, Thailand for a night of booze, dancing, and debauchery. But the moon-themed antics of these party-goers look positively tepid when compared to those of the Great Barrier Reef’s corals. With the help of two genes and a spot of moonlight, the corals synchronise one of the greatest spectacles of the natural world – a mass annual orgy.
When it comes to sex, corals play a numbers game. Encased in their rocky shells, direct contact is out of the question so they reproduce by releasing millions of eggs and sperm directly into the surrounding water.
This strategy only makes sense if all the corals release their sex cells en masse and sure enough, every individual within a third of a million square kilometres of reef does so during the days after the October full moon.
The corals’ co-ordination would put even the most organised flash-mobs to shame and until now, scientists had no idea how they did it, especially with neither eyes nor brains. Aside from the obvious contribution of moonlight, the only other available clue was that corals seem to be especially sensitive to blue light.