Siren Singing
To make a boy follow them

Siren Singing is an ability that allows a mermaid to put a boy in a trance that makes him follow her. In the girls' pod, the Enchantment Song was forbidden.

The only way to reverse the Enchantment Song for the Southern pod is to blow into a particular shell. Rita has this shell but Lyla and Sirena broke it, but they find another shell that is identical from Rita's and they use it to reverse the spell. Moon-induced Siren Singing is reversed when the Full Moon sets.

For the Northern Pod the Enchantment song was broken when Ondina and Mimmi sung another song above Sirena to break the hold it had on her. If the Enchantment song is from a pod that you originate from then that mermaid is immune to its powers while other mermaids are succeptable to its magic. If a mermaid is under an enchantment then they will find a boy so they can be together forever. A side affect of this was probably the drowning that sailors experienced since they were unable to hold their breath for as long as a merperson. Once the Enchantment has been broken the mermaid who was affected will be dissoriented and won't remember what has happened since they became enchanted.