I love underwater scenes because they give SO much opportunity to explore color and different planes of perspective. Your style is very graphic and it comes out nicely here.
I love love love the turtle you created... his pose is excellent and in perspective. He is sort of mimicking adam's pose and that is so fun.
I did a quick paint-over (I hope you don't mind) because I thought you had a great start here. I think that some of the design issues are worth working out.

Here I have them side-by-side so that we can see how things have changed.
Firstly, all of the eyelines of the fish and Adam are all over the place. I sorted them out to help secure the impression that adam is looking at the fish and they are all looking back at him (he is probably the first naked dude they have ever seen!) I also blew away the little shark in the middle that appeared fully frontal to the view pane... he was the only figure in the piece in that pose and it felt super confrontational and a tad distracting (also, he might've been too close to the gutter.)
Secondly, I varied the size of the fish somewhat. This gives a little more impression that they are all in different depths in the pane. Also, the octopus (very cute) seemed a bit trapped in the lower right, so I moved him toward the viewer and painted out some more structure to lead into the piece a little more.
Thirdly, I drew over some skeletal reference lines onto Adam to diagnose a little issue that I felt with his hips (hidden) and the length of that far leg... I shortened it a bit and painted away some of the coral to give his toes some breathing room. I felt like there was a start of a distracting tangency there.
Next I addressed the atmospheric perspective in the piece. I desaturated and lightened the distant shapes as well as darkened and saturated the nearer elements. This lends a little more feeling of distance.
Overall, I think this would be a very fun story to tell. Nice work! I can't wait to see more.