They can’t have sex or reproduce in Mermaid form due to having no genitals. In the days before the impending doom of the lost continent of Atlantis the Wizard Mermis prepared his survival plan for its citizens. A mystical transformation into Mermaids, and Mermen so they could go on living in the seas forever! Mermis saw that the quest for sex, and it’s continued obsession, stood in the way of societal advancement. So he purposely decided the new race would have no genitals. That is except for brief times as humans when procreation was necessary to carry on the supernatural species.
Only at the stroke of Midnight during a Full Moon may they come ashore to mate. They become indistinguishable from humans beneath the waste while basking in the lunar light. People happening upon couples making love on the beach under a full moon may have in fact witnessed mermaids mating. The phrase for mermaid sex is “Alcyone Ceyx” or sometimes just Ceyx. Alcyone is the Greek Demi-Goddess of the sea, and moon. Ceyx is her husband. It is a sacred ceremony generally only partaken of twice in a Mercouples life. Each mating is meant to give one baby of each gender to keep the populace at 50% male, and 50% female. A conception always takes place but the pregnancy is virtually imperceptible to the eye, and could last anywhere from one month to over a year.
Unfortunately a mermaid baby can only be born under the light of a true blue moon! This is why there are so few mermaids. It must be the next blue moon so love making under a blue moon doesn’t create an instant birth. On the night of the full blue moon a mermaid will come ashore near the water’s edge. This is only on an area where the moon is actually blue hued due to various mystical forces. The Mother, Father, Siblings, Grandparents, and a birthing witch doctor come ashore on a secluded beach at the Witching Hour. There the Birthing Ceremony takes place as all are in human form. Although most family members, and friends remain in merform at the waters edge. A canal is dug in the sand from the mother to the water. The baby is born into the sandy canal sliding down into the water where it quick takes Merbaby form in the designated Godparents arms. The parents, and the rest of the birthing party then enter the water to take possession of the child.
Legend has it that a newborn mermaid baby stolen away, and bathed in fresh water within 24 hours will permanently become a Mermaid Shapeshifter. In essence a superhuman who can change into Mermaid form at will regardless of salt water immersion. There is only one sparse record of such a being in the secret supernatural record. Apparently back in the late 1500’s Spanish Conquistadors kidnapped a Merbaby in Mexico. It’s unknown if this special person still exists today.