Corey has already lost one friend to the sea. Even though he and Gabriel Braven are mentally connected they will never both live on land again. So he is the closest thing to an expert there is for those Mer-human hybrids to talk to about the costs and gains about transitioning.
Corey is also the unofficial ambassador for humanity to the Mers. Somehow he has to keep peace between the driven and desperate Dr. Cleave and the remote and suspicious Lord Aemrys. When it comes out that that Spencer's father is a member of the reviled and exiled Mer House Aer, Corey has his hands full.