Conservation means to preserve something.
Most things brought up from the sea need to be preserved if they have been on the seabed for a long time, otherwise they crumble away. The job of the conservator is to make the object stable again - to preserve it. Once a ship wrecks, the ship and the objects on board her start to decay. Metal starts rusting and wood gets eaten away by sea worms. Sometimes they will be protected by a layer of sand or mud, and as long as nobody disturbs them, objects will be preserved on the seabed.