First of all, I think this is a really nice shot and the pose of the octopus(?) is really cool. You probably tried cropping out just this guy in a vertical, maybe even b/w. Almost looks like (s)he’s ashamed of skinny-dipping…
I don’t know a lot about UW photography, but I am not sure that more shadows necessarily translates into greater perceived depth. Your strobe is off-center already (towards the top left, shadows are a bit to the bottom right). I think the suggestion to go a bit lower yet is a good one, maybe it’s not that easy when freediving to try a couple of different angles.
But as said above, definitely a great moment to capture!