HI Max, welcome to Wetpixel!
I like the images you chose to post, they are an interesting mix. I can tell you what I would think about if presented with these same opportunities, whether or not my recommendations make sense to you is your call. ;-)
The first image has tons of potential, multiples are almost always more interesting than singles. The orange background is a nice opportunity too. I would have tried to get closer and fill the frame with the morays and just the orange negative space. The brown doesnt do much for me. There are lots of options for the light direction here. It would have been a lot of fun to play with and try different alternatives for strobe angle. Definitely closer though.
The octo pic is fun too. As it is the balance seems off. Id try cropping it with the eye right in the middle horizontally. The fuzzy left bottom corner is distracting to my eye. Id try applying a vignette to darken the corners and bring the viewers eye to the subject. I would have thought about trying to light the octopus without throwing light on the rock behind her/him. A slightly different orientation with the bright orange below the eye or just off to one side of the siphon would have been fun to play with.
I love the anemone. Thats the kind of photo opportunity we could play with for hours. As it is the out of focus clump in the foreground hurts the image for me. Great choice of subject to spend some time with.
The first yellow goatfish school shot has all kinds of potential. I like the way your eye works to see that image. The color looks a touch too saturated for my eye but I like where you were going. The lines up the middle really hurt the flow and balance for me. Another image opportunity that deserves some more work when you see it again.
Im curious, how many shots of these subjects did you take?