Overall I really like the art style, and the gameplay loop centered around exploration is really cool! It took me a long time to figure out how to buy upgrades, and it was a little frustrating having to move slowly towards the upgrade islands one at a time, so maybe a centralized shop area would be nice. Also, the hitboxes on the spikey guys are deceptively big and always caught me off guard. It seems like 2 of the levels are missing wall hitboxes underwater? And I couldn't reach the mysterious fourth upgrade because the island leading to it walled me off. And pressing G to win the game at the end took me a very long time to figure out lol. Maybe if you just automatically won when you talk to the questgiver?
Even despite running into these issues I had a lot of fun exploring the ocean and finding treasure!! Very good job with this!!