There shouldn't be any purple as water isn't purple, the air tank on the scuba diver shouldn't look like a battery, the mermaid shouldn't have goggles on since her eyes are accustomed to seeing under water and the hole she's coming out of should actually look something like a cave. The only things that look good are the hair, bubbles, seaweed and the diver.
oh wow....i LOVE your approach to this: fluid, loose, squiggly...i kinda like it this way. the bold thick strokes....this is probably too late to say but i guess my only suggestion is her awkward head. the fact that it's tilted like that and hair is blocking her neck makes it feel like it's floating. other than that, i just like the graphic feel to it.