One of Ariel's greatest treasures is arguably her voice.  While she finds herself stranded without it, quite another type of Disney hero finds himself stranded on an island.  While it may not be the treasure he ultimately seeks, there is a liquid "treasure" stranded with him.  Head back down to the bar and stand in front of the bar facing this "treasure".  Slightly to your left eyeline you will see a treasure chest.  Open that and look inside for your next clue.