An interesting little experience- The difficulty was kind of a downward curve, as the jellyfish were much more threatening than the sharks, though you mentioned that was a necessary sacrifice. Beyond that, the music seems oddly ominous for such a cute game.
Cute it is, though- I quite like the graphics and the sound effects for the starfish (which is a fun little pun), and the super-simple "story" may not be to everyone's taste, but I personally liked it.
This game was also clearly a learning experience, so keep it up, and keep getting better!