Nice!
The whole transformation thing was a nice concept. The deeper sea could probably look a tab bit better if it was a tad bit darker, but it's no biggy. The perspective was well drawn, and the seaweed looks nice. It might be just me, but the left hand of the "first" person (the one closest to the bottom) looks like it only has 4 fingers, while the right has 5 (speaking of which, the ring finger looks slightly chubby).
I liked the colors (I'm a big fan of blue), and this is probably one of the best underwater pieces I've seen. Fantastic job~