That's a great start, René! The light and colors are wonderful. I'm pretty sure you know what to change, but I'll mention some things anyway that come to my mind; tiny bump holes on the corals at front, more raggedness in the rocks, and there seems to be a sharp distinction between waves and 'water' up left.
I wonder how you did the floating dirt, btw, which is really making it more real. I can imagine a few ways, but I'm just curious.