I'll start by saying I'm not a fan of mermaids, but I actually like this piece. I like her position and the detail in the coral and fish.
I think it's a very lusty, romantic, daring piece in some aspects.

There are a couple of things I think need work though, the lighting, I can see where the sun breaches the water but how is the side we see lit up, I think shading is needed a little more here. I like her necklace but I think the glint is facing the wrong way. The last thing I don't really care for is the treasure chest, I get the idea of it but I think the way it was incorporated is not top-notch. It just seems kinda tossed in there for effect and not as a real part of the pieces, focal or otherwise.

I like her hair a lot, I find you're hair techniques blow my mind, I think her hair should be in a different position if she's underwater but I still find it enchanting. Good job and beautiful piece.

Overall it's very good. I feel it's very romantic and admire the manipulation technique used for making the mermaid. I also like the various shades of blue and the fish. This combined with the background lend authenticity to the scene.

There are a few things I probably would do differently. First, considering there is such a visible light source, I would probably have played with shadowing a bit more, especially around the mermaid. I would have added slight shadows to and around the fish. As the image is now, it's kind of flat, but shadowing along with the lighting would have given the image more depth.

In any case, it's a really lovely manip and you did a great job.