The Update 1.4.0: Update Aquatic - Phase One Title update for Minecraft (iOS) has 8 achievements worth 200 gamerscore.
Visit all ocean biomes
Eat nothing but dried kelp for three in-game days
Collect a fish in a bucket
Find an underwater ruin
Find a shipwreck
Spend a day underwater.
Power a furnace with a kelp block
Dig up a buried treasure