Corals feed, hunters come out, and the water itself can light up when you move.
Hard coral looks like rock during the day because its polyps are retracted. After dark they extend to feed, and the whole reef surface turns furry and mobile. It is the single biggest visual difference between a day and a night dive, and most people are not prepared for it.
The cast changes too. Parrotfish wrap themselves in a mucus cocoon and sleep in crevices. Moray eels leave their holes and hunt in the open, which is the only time most divers see one swimming. Spanish dancers — large red nudibranchs — come out and occasionally swim, which looks exactly as improbable as it sounds.
Bioluminescence is the extra. In the right conditions, switching your torch off and waving a hand produces sparks of blue-green light from disturbed plankton. It does not happen every night and cannot be promised, but when it does it is the thing people talk about for years.
In the right conditions, switching your torch off and waving a hand produces sparks of blue-green light from disturbed plankton.
Night trips are usually run from a moored boat on a familiar shallow reef, with a torch each and a guide leading. Snorkellers can do it as well as divers — the shallowest part of the reef is where most of the action is anyway.
