Once upon that the Ocean Ruins were inhabited by villagers that became drowneds like the ship crewmates that transported hearts of the sea and tridents.
The ocean monuments also were on land, the guardians were the now forgotten Reepers that controlled the jungle and the temple was functional then, but an evil force created a tsunami that destroyed all the civilization except the kicked villagers that lived on the plains, far from the disaster. Any evil fore tried to kill the Ender Dragon, a warden of all the dimension. This day the evil Wither sent the tsunami and destroyed the ships, a good thing is the crew of the ship have hidden buried treasures.