Nice little gem!
I like that the game is simple but still challenging. It takes some time to figure out exactly what you are expected to complete before oxygen runs out. You also really feel a sense of greed in the game with a great execution.
I think it would be even more interesting if you could get up to a non filled level and regain the oxygen meter. This way you really could make trips down into the ship and gather treasures.
I think I laid an egg in the end...
Some more polish and touches to make it really awesome!
Good job!