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