Yeah, masterpj, I saw your post. I also gave a thought about animating a "flow" of particles bouncing off manta. But then if a manta will have a background - then that "flow" will be a bit excessive, I think. But the bubbles - ooh, those bubbles. :-) More than that, If you turn gravity towards the viewport (camera) or animate particles' size to enlarge, and add a bit of chaos - then the whole animation will look more cartoonish.
If the manta is animated in move, ofcoz - not only waving its wings like a retard.
P.S. About cartoonizing images - I've had an idea to render at 15fps and add a little XYZflickering to whole scene to make it look hand-drawn, but lack of free time kills all the ideas.