Board Thread:General Discussion/@comment-25850402-20150723062747/@comment-25758988-20161215214913

I dont actually think Mermaids have any specifically individual magic with the exception of creating portals between worlds and their voices. This is a by product of their species, similar as to how Dragons can breath fire. The shells being used to summon storms and communicate with other sea creatures is a water based magic. I think the seas of the Enchanted Forest are as full as magic as the air around the surface that generate Dragons, Dwarfs, Ogres, Trolls, Fairies, Werewolves and Enchanted Trees. I mean in the oceans we have Giant Squids (which generate extremely powerful squid ink), we have Monstro, Ursula (sea witch) Sirens and Mermaids. Poseidon or even Ursula may have created the shells and I believe that only she or Posidon can turn Mermaid's human. I know we saw Regina give Ariel a bracelet but I doubt she created that herself and prob got it from Poseidon at some point or while in her Ursula guise stole the bracelet from his vault.

It is also worth noting that Poseidon does not seem to have the ability to create a portal to other worlds and needed a mermaid to do it for him, so even his powers have their limits.

This theory comes from what August tells Emma about that if anything had magic in it it would be water.