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