Barnacleskin

The power of the watery deeps courses through you. A crust of barnacles encases your skin, providing you with a bonus to your armour class equal to your Charisma bonus + 1 for the duration of the spell.

As your connection to the fathomless deep grows, the benefits of barnacleskin increase with your Sea Sorcery level, eventually granting you the ability to survive the deepest, darkest briney depths:

Sea Sorcery Level 5: AC bonus equals your Charisma bonus + 2, and you gain resistance to cold damage.

Sea Sorcery Level 11: AC bonus equals your Charisma bonus + 3, and you gain resistance to cold damage.

Sea Sorcery Level 17: AC bonus equals your Charisma bonus + 4, and you gain resistance to cold and force damage.