Reunion (Water #2) by Kara Dalkey

Pre-loved paperback

The sea is the birthplace of legends. Corwin has spent all of his sixteen years scavenging the land for his next meal. But when he discovers a unique shell of exquisite beauty, he is convinced it will bring him the riches he's longed for. His hopes are dashed when the shell is stolen from him by evil King Vortigern's men. But the shell has left its mark. Corwin's head is filled with visions of a beautiful and mysterious girl. Soon, he comes face-to-face with the girl of his visions -- Nia, a mermyd from the ocean's depths, the lost city of Atlantis! Together, Nia and Corwin must search for the stolen shell, for it holds the key to the future of Atlantis and also to Nia's and Corwin's very survival.