Most people don’t spend very much time considering the coral reef at night.
The daylight reef swarms with activity – fish and corals, along with other invertebrates of every shape and size.
At night, the fish are mostly sleeping, but other creatures come out to play. One example: bristle worms. These stinging invertebrates hide in crevices during daylight hours, and emerge at night to clean detritus off the reef.
The corals change by night as well. This green star polyp colony looks full and bushy by daylight….
… but those fuzzy polyps pull back into themselves almost completely within minutes after the lights go out:
Even the fish look different at night. Thing 1 the pipe spends all of the daylight hours cruising around the tank, looking for food:
But for pipefish, sleeping involves hanging vertically in the water, imitating a strand of sea grass:
Some corals do exhibit almost as much show by night as by day–most commonly, the specimens which are naturally nocturnal but which learn to open diurnally due to feeding patterns in a captive reef. A good example is the blue sea fan, open here at feeding time:
And here a couple of hours after the lights go out for the night:
I hope you’ve enjoyed this glance at life on the reef by night, as opposed to the daytime shots I usually offer. Did any of the images surprise you?
The pipefish sleeping “standing” up cracks me up. Does it grab onto something to hang on to? Why doesn’t it just float to the top when sleeping? Or find a cave? I guess while sleeping the animals could be very vulnerable to being eaten.