Patricia A. McKillip 
Changeling Sea [EPUB ebook] 

Since the day her father’s fishing boat returned without him, Peri and her mother have mourned his loss. Her mother sinks into a deep depression and spends her days gazing out at the sea. Unable to control her anger and sadness any longer, Peri uses the small magic she knows to hex the sea. And suddenly into her drab life come the King’s sons-changelings with strange ties to the underwater kingdom-a young magician, and, finally, love.