Here's a fascinating time-lapse video of the slowest underwater life, speeded up to show its movement and activities.
The author says of it:
"Slow" marine life is particularly mysterious. As colorful, bizarre-looking, and environmentally important as we know corals and sponges are, their simple day-to-day life is hidden. We know some bits about their biochemistry, corals’ interaction with zooxanthella algae, their life cycles, and systematics. Unfortunately, it’s hard to tell what we don’t know about the rest, and particularly when it comes to interaction with other organisms happening over long periods of time.
Time lapse cinematography reveals a whole different world full of hypnotic motion and my idea was to make coral reef life more spectacular and thus closer to our awareness. I had a bigger picture in my mind for my clip. But after many months of processing hundreds of thousands of photos and trying to capture various elements of coral and sponge behavior I realized that I have to take it one step at a time. For now, the clip just focuses on beauty of microscopic reef “landscapes.” The close-up patterns and colors of this type of fauna hardly resemble anything from the terrestrial environments.
There's more at the link. It's very interesting reading if, like me, you don't know much about the field.