To explain the title a little better - most of the oceans are in total darkness all the time, and even the sunlit zone is an inky realm every night when our star visits the other side of the planet. Accepting that we can't easily visit the bathypelagic zone (the deepest bits) without submersibles or ROV's (remotely operated vehicles), then perhaps the best feel we can get for what's happening in the vast majority of the oceans is to don SCUBA gear and dive the surface of the open ocean, but in the dark. In preparation for doing a bit of that later this year, I've been looking at "black water night diving" stuff on YouTube. Honestly, the idea invokes in me a healthy amount of fear, but if these videos are anything to go on, then I hope that will soon be replaced by wonderment and fascination.
Pelagic plankton. I love the flatfish at 0:28. If you know what the spongy looking thing at 1:40 and 4:04 is, please let me know.
Humboldt squids - I especially liked the face-on attack at 2:00 and the strobing at 2:30
I guess this is the most obvious anxiety. The one at 1:20 just gives me the heebie-jeebies!
This video isn't so much pelagic as reef, but the spawning sea cucumbers and then the palolo worms about 5:40 in are just great, and I love the music, which (curiously) is from that abysmal Mel Gibson flick Passion of the Christ.