I am a still learning, but willing to throw stones...
first turtle pic is subjectively awesome. Turtle is hidden / emerging via the soft corals. Kudos! Lighting and color balance gets distracting after a while. I wanted a black background and more central lighting.
Second picture i got distracted by the color balance, especially the background. You can see some red from the very close coral, lots of blue background. But very good framing. I like non cropped pictures!
Third pic - angelfish - always tuff buggers cause they move too much. You have great physical composition (always tough), but the color does not jump out. Combo of sand bottom and too much backgound ambient lighting? More flash, less ambient would help.
Lobsters? Maybe? These are hard to get a GREAT picture. I have lots of barely okay, nothing great yet. This picture looks like the flash lit up the coral above the lobsters, and a little on the lobsters. The sand below is "greenish". (Sand is your enemy!) I think you need to get several feet closer to get a good shot. If a lobsters feeler is not smacking me in the head, then I think I did not get a good shot.
Squirrel fish: Again, pretty good composition, but poor lighting. The flash is illuminating the top of the shot. I want it to illuminate the squirrel. I also want the "blue: background to be black.
Your composition is very good (more than half the battle - i am still working on this...)! I claim you need to master lighting. Or not!
In general I think you need to rely less on ambient light light and more on your strobe. This will make your subject and the colors pop more. Or go the other extreme and rely only on ambient light. There are lots of awesome ambient light pics out there.
Think about how each of these pictures would look like if the "background blue" was actually black.
The "black background" is a concept I only learned about recently. It helped. Technically, I went from auto ttl flash brain to fully manual strobe brain (almost). I am much more happy with my recent shots. The colors are more vivid and black background draws the viewers eye to my intended subject.
Keep shooting, keep asking.