Nice idea of having the harpoon to use as a weapon and tool. I found the movement on the seabed very stiff and slow, only constant jumping made it slightly faster. The harpoon seemed to work well and it's fun to use in inventive ways. There are also some nice touches that not many jam games have, like the bubbles.
I'd like to invite your game to our contest, the Game Development World Championship! We happen to have a special category for jam entries from this year's jams.