Good shots.
I like the curves of the shark, giving the image a feeling of motion. Also, the deep blue background is impressive. It feels a little boxed in, though. Is this cropped.
The space in front of the turtle is another good composition for an action shot.
The green moray is a little odd on the lighting, in my opinion. The two tone affect kinda makes it look like its coming out of a second liquid surface.
The dolphin looks a little muted, but maybe that was your preference.
The grouper has a "mounted on the wall" look (very straight and complete lateral view), but the lighting is good.
My favorite is the last shot, good space and positioning of the lone diver. 
S