This was cool! I liked the graphics and the attention to detail on the high seas like the shipwreck on the island in the South East and the wrecks in the rocky areas. Good work with the upgrade system and random enemy spawns.
My only suggestions would be that a pause button would be nice and maybe some more realistic sound effects. Oh and I bumped into the black pirate ship for fun, but nothing happened - not sure if that was intentional.