I love Kelp Forest, it reminds me of the Baba is You soundtrack with its mesmerising synth parts. All of the songs have a really good atmosphere, sort of ethereal, which fits really nicely with the image theme.
One thing that may or may not make some of the songs even better would be to add a bit of background ambience, similar to what you did on The Undersea, to hammer home the feeling of being underwater and to fill out the mix a bit more. This is just my opinion though, overall this is a really good entry!