To me, it's not clear that the character is underwater.
As Robinhood said, schools of fish at the top might help with not only the emptyness, but the lack of... underwater-ness.
Good attempt though.
Slightly rough looking, but wonderful job overall :D
Top part looks a bit emtpy... Schools of fishes?
This is so rad, I love the rocks and all the color use, and the HUDs are great