Hello, really love the game and hope you keep on developing it.
I know it's early days yet but here's some ideas I'd like to see,
Day/Night cycle ( more dangerous at night ) , will need lights.
A dredge, rope and metal, throw in and drag back to scavenge items on the sea bed. ( maybe different metals )
Crab pot, throw in and wait.
Diving, items on sea bed, very dangerous
A diving weight, get down faster
Reinforced wood, takes 2 attacks to fail
More items to craft/build with some sort of automation eventually ( conveyor to empty nets into chests... that sort of thing )
And what about a dolphin, feed it and it brings you items or chases the shark away for a while.