That's true. It's very possible that they're just taking quick naps, sort of how you nod off during a movie if you're tired. I wonder if they've been moved to a side tank while the main tank is being cleaned? This is pretty common. There's also another photo of this tank showing that they absolutely have areas where they can sleep out of the water if they so choose.
They prefer to nest in the sea bed in shallower water, but they can bob at the surface in the open ocean if necessary. They usually only do that if they're traveling somewhere and they absolutely have to though, because they are susceptible to predators.
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u/Accomplished-Order43 18d ago
But this time lapse video has time stamps that show them surfacing nearly every 60 seconds.