Witchy: Translation was pathconstrained, rotation was manually keyframed (subject to change, not fully happy with it).
Icarus: As for the seabed being barren, I will add more stuff, possibly some seaweed and stuff, but it will be fairly clean by design.
Zykotik: Youre talking about caustics, and 'god rays'? Maybe I'll add those later, not sure though.
I'm using one of kbrowns nifty MEL-snippets to fade the particles opacity based on distance to camera (plus some stuff I added myself).