Do the creatures that live around hydrothermal vents sleep (or display circadian rhythmic behaviour)?

Question

I'm wondering that if circadian rhythms evolved due to daylight have these creatures living in a constant environment evolved away from it.

Answer 1

I'm not aware of any studies on the matter, but at best guess, I can't imagine any reason why they *would* have a circadian rhythm unless it was a natural cycle that wasn't prompted by any particular change. Down that deep, there's no change in light, and the temperature remains pretty constant next to the vent. Unless the vents were more active at a particular time of day or something, the animals down that deep would have no cues to follow. Even the marine snow is supposed to be pretty constant. If they *are* on some sort of cycle, it's probably not exactly circadian or diel or anything like that. It's probably for health reasons, because frankly, everything needs to rest now and then.

Answer 2

I don't know if observations have been taken for a sufficiently long period to establish periodic sleep or circadian rhythmic patterns. There have been some fish species found in caverns with streams that are blind, but again, I am not aware of studies on them either.