To my understanding, according to the wiki, dolphins are attracted to buried treasures and the chest(s) inside of shipwrecks and ocean ruins. When the chest is broken, the dolphin will locate new treasure. This is not the case. Maybe it takes a long time for the dolphin to receive an update, but after practically removing every single block of an ocean ruin/shipwreck/buried treasure, the dolphin still swims to the same structure when it is fed cod. I have tested this in many worlds on several ocean structures.