OMFG. How DO mermaids make love? That's so weird... My theory is that they all go to Ursula and like, trade one of their traits for a humane body for a while. Then they go into the human world, fall in love and all that shit, and then make love.. While they love each other more and more, the mermaids tell their loverboy whatever they are missing can only be retrieved at the bottom of the sea (if they can speak, if not they would have to write it down) and if the boy is really worth it, he will go and get that back off of Ursula and give her some gold seashells in return.
:)