J.P.
An ocean theme would work too. You could keep it simple with 'water' color paint and decals that can be removed later. You can usually find fish, maybe even mermaids and pirate ships. Accents for the room should be easy to find (seashells, nautical). Have fun! I love doing a kids room, it's easy to go crazy with themes.
Oh, and stars on the ceiling would be fun - glow in the dark or a light display variety.
My son has a race car bed, but he loves pretending it's a ship sometimes. In a ocean room I would try to make the bed/bunks look like a ship somehow.