I like the settings you've created here. Very good balance in the composition. The lighting is a bit on the harsh side though. It's touch on some of the textures on the lighter shells. Try it again with softer ((and) or less) lighting and you will have a hit as far as I'm conserned at least. ;)
This is such a wonderfully simple photo of something I love (which is almost anything that reminds me of the ocean). I'll be looking to see more of these. (I hope!)