Merpeople are human/fish-hybrids, the legends of which go back more than three thousand years. They're magical creatures of the seas, and the basis for the hit television shows H2O: Just Add Water and Mako: Island of Secrets. According to Sirena, the natural merpeople are born in the sea.
On special occasion, the Moon Pool will react to the Full Moon magically and unleash special effects, such as taking away a merpeople's powers temporarily or forever, or enhancing a merpeople's powers.
Physiology
Cleo, Rikki and Bella as Mermaids
All merpeople share the same basic traits.
When mermaids come into contact with water for ten seconds, they grow a long copper-golden-orange tail and a matching top. Their tails are covered in scales and end in a classic dolphin-shaped fluke. They also have a short dorsal fin running along the backs of their tails from their waists to a little more than halfway down the tail.
When mermen come into contact with water for ten seconds, they grow a long light-blue tail. They also have a short dorsal fin running along the backs of their tails from their waists to a little more than halfway down the tail.
The merperson's tail is also very strong, this is shown when Emma saves Zane Bennett by smashing in the steel door on Miss Chatham's boat, or when Nixie broke the iced surface of the pool in the Grotto.
Zac as Merman
They also lose their clothes they're wearing in human form which only reappear when they become human again. There is a possibility that they could absorb their clothing into themselves as a side effect of their metamorphosis into merpeople. Their hair keeps it's natural color and length, but any hair-ties, headbands, hair-clips or hairspray disappears, along with their clothes. When they dry, their hair will return to whatever hairdo it was in. When they transform they hair starts out untangled. If the merpeople wets only part of the body, then the hair will stay dry after the transformation; however, if the whole body gets wet, then the hair will look wet as well. The Moon Rings accompanies the merpeople's transformation, ie, if they have a human form and transform, the Moon Ring is still there and vice versa, indicating that the ring is a magical object.
The transformation also occurs when merpeople are exposed to snow, but since southern merpeople never interact with snow, they will also develop snow rash and become feverish. The only way to cure them is by applying dried seahorse powder onto their skin.
Pods
Members of Mako Island's Pod honoring the moon
As revealed in Mako: Island of Secrets, there are Pods of natural born mermaids all around the world. The Mako Island pod consists of over a hundred. When the moon is full, the natural mermaids all around the world, honor the moon with a ceremony. The natural born "real" mermaids, unlike transformed humans, live on a seafood diet and wear seashells as jewelry. The mermaid council has made laws with Veridia as the head of the council.
Some of these are:
It is forbidden to sing the Enchantment Song. (only in Mako Island Pod).
It is forbidden to associate with land people and it is especially not allowed to use a Moon Ring to go on land.
It is forbidden to let land people come onto Mako Island on a full moon, and it is even more forbidden to let them into the moon pool.
It is forbidden to fall in love with a land person.
It is forbidden to go near the coast.
It is forbidden to reveal your powers to mortals.
Sirena, Lyla and Nixie broke the rule of not letting land people on to the Island and were later blamed when the pod found out that Zac had also fallen into the Moon Pool when they were supposed to be guarding it. They were then cast out of the pod. Later in season 1, they broke the rules of singing the Enchantment Song and using a Moon Ring to go on land.
Rita teaching the girls
Mermaids of the pod use the full moon as a source of magic and power. They created moon rings out of the blue crystals from Mako and they use them for both destruction and healing.
Young mermaids in the pod have to train to be worthy of the use of these rings. This "Mermaid School" teaches them to use their powers correctly and to be sensible in the difficult choices made through mermaid life.
Rita Santos is a teacher on land, at Suncoast High, but possibly could have been a mermaid teacher when she lived in the pod. She helped Lyla, Sirena and Nixie finish their training and gave them their own Moon Rings.
The Mako Island Pod fled Mako in "Outcasts" and joined another pod in the South Pacific. Lyla, Nixie and Sirena are waiting for them to return now that Mako is safe for mermaids again.
Mermaid Council
Mermen are from a long line of ancient merman. They are different as they are raised on land. They are raised in foster families and travel together. They go to land school and mingle with humans.
It is still a mystery how the H2O: Just Add Water characters didn't happen to come across the pod during their period of time living on the Gold Coast and going to the Moon Pool regularly, let alone notice Lyla, Sirena, Nixie and Zac who went to Mako every full moon in their time. The only theory fans can think of is that the events of H2O and Mako Mermaids happened in different time periods. It is possible that the H2O characters left the Gold Coast to lead separate lives and become adults before the Pod came to live at Mako. The moon pool seemed to be somehow changed and made into a home by the mermaids, becoming "a sacred place."
Rikki, Cleo and Bella's hand movements of their powers
All merpeople have several common powers and abilities.
Transforming Ability - They all have a transforming ability, in which they have absolutely no influence, 10 seconds after they come in contact with water. If all water is removed (dried) from the merperson's body before the 10 seconds are up then the merperson will remain in human form. But if not dried, the merperson will grow a tail. The same thing will happen if their skin is touched by snow.
Underwater Breathing - Merpeople can stay submerged for long periods of time but they still need to breathe air. Merpeople can hold their breath for at least 24 hours before needing to resurface but with more practice merpeople can stay under for much longer. When mermaids stay breathless, they do not die, unlike humans. They "sleep" underwater, and just awaken when they breathe air again. They can only hold their breath in merpeople form. When merpeople are infected with Fish Fever, they undergo changes and grow gills. It is possible that during this time, they can actually breathe underwater.
Durability - Merpeople can swim days without getting exhausted.
Speed-Swimming - In water, merpeople also have the additional ability of Speed-Swimming. When a merperson speed-swims their body is enveloped in bubbles that they use as a jet stream with which to swim quickly. This can be a great advantage when trying to flee from enemies such as another mermaid/merman or boats and other water crafts. It is also called "torpedoing."
Dolphinish - Some natural-born merpeople have the unique ability to comprehend and speak the language of dolphins. The merpeople are born with this ability, it's unknown if it can be learned, but probably not. Nixie and Sirena are known for demonstrate this ability.
Volume Reduction- Is the ability that all merpeople are shown to have. With this power, merpeople can shrink things.
Invisibility - Invisibility is a power that all merpeople are shown to have. With this power they can turn temporarily invisible. The user is capable of staying invisible with legs or tails, in or out of water.
Siren Singing - Siren Singing is a musical/voice-related magical ability that allows the user to put a person (usually a man) into an irresistible, hypnotic trance in which he will follow the mermaid around or obey the mermaid's whim and desires without question. In the Mako Island's Pod, is forbidden the use of this skill. Is a natural skill, and can not be learned. Humans that have been transformed in mermaids, can demonstrate this skill when affected by the Full Moon.
Cleo, Emma and Rikki's hand movements of their powers
It is possible that the place where the merperson's transformation happened affects the powers over water, e.g. the Moon Pool at Mako Island gave the people the power to control, freeze and boil water, but the pool in the Sea Caves of Ireland where Bella changed gave her the power to turn water into a jelly-like substance and to turn water into a substance similar to crystal or glass.
Weaknesses
Sirena and Lyla with Snow Rash
Snow Rash - Natural merpeople such as Lyla, Nixie and Sirena that were born in warm waters, have never interacted with snow. If they do end up going into contact with it, it will make them develop Snow Rash, a moss-green rash caused by contact with snow. It is accompanied by itch, fever, and malaise and doctors such as Dr. Blakely couldn't realize what it was. It is not known whether a human transformed into a merperson by a Moon Pool also develops the disease. It was first shown in Mako Mermaids. It seems to be very fatal to Southern Mermaids. It is also likely that merpeople born and raised in icy waters develop some immunity to the cold and also on Snow Rash. Rita said the girls were "Southern Mermaids" and this implies that there are also "Northern Mermaids". The only way to cure this allergy is a Dried Seahorse Powder that Rita contains stored within a silver seahorse. To heal, the dust must be sprinkled on the affected part of the skin, and it will immediately disappear.
Emma Infected
Fish Fever - Despite not being under the influence of the Full Moon, Emma once again developed a craving for raw fish and seafood in the episode "Fish Fever". While helping with the search for a coral for Cleo’s new fish tank, Emma accidentally cut herself on a strange, rainbow-colored coral. Unknown to the girls, the toxic coral can affect a merpeople tremendously. At first, it caused her to be overexcited, but the more the poison seeps into Emma's system, the more ravenous she gets. The poison also caused a tremendous mutation in a mermaid's physical system. For Emma, her copper-golden-orange scales turned white and scales even appeared on the skin, her hands became webbed, her nails turned black and later into claws, her skin became more monstrous, her neck sprouted a set of gills, her hair started to turn green, her eyes turned yellow and she made monster-like noises. She also developed a desire to be wet. She was later totally cured when Lewis sprayed an antidote on her skin, which was developed by Laurie. The fish affected by coral's disease, and its scales will turn white and they will develop a hunger out of the ordinary, as Emma. Laurie said that Cleo's fish named Hector, was not cured in time, he would have died. The same goes for the merpeople, in the case Emma. When merpeople is infected with Fish Fever, they undergo changes and grow gills. It is possible that during this time, they can actually breathe underwater.
Ambergris
Ambergris - Is an old substance that at one point in time was used to make beauty products such as ladies perfume. It comes from the intestines of a whale and it can be used to attract mermaids. In "Irresistible", Zane Bennett finds some old ambergris which Nate later tries on. The smell from the ambergris makes him stink but it also makes him literally irresistible to Cleo, Emma and Rikki. Ambergris was also one of the ingredients used in Mimmi's potion of fifty moons to remove Zac's powers.
Merpeople Magic
Mermaid Mythology Book
Merpeople posses several magical abilities that Cleo, Emma, Rikki and Bella find out about along the way.
With the help of Lewis McCartney the girls found a book, "Mermaid Mythology" that held a recipe for a Mermaid's Potion that could give mermaids the power to grant wishes. The potion was made using specific types of sea algae along with an equal amount of each mermaids powers. The potion had to be smeared on one of the girls faces while they were in mermaid form for the wish to come true.
Ambergris is an old substance that at one point in time was used to make beauty products such as ladies perfume. It comes from the intestines of a whale and it can be used to attract mermaids. In "Irresistible", Zane Bennett finds some old ambergris which Nate later tries on. The smell from the ambergris makes him stink but it also makes him literally irresistible to Cleo, Emma and Rikki.
Sirens are mythological women with voices beautiful enough to entrance men. In "The Siren Effect" when Cleo saw the moons reflection she went into her bathroom and touched water in the sink. While she had absolutely no musical talent previously, she then had the voice of a siren. She sang a melodious songs that literally entranced all the boys in town. This fantastic talent however disappeared when the full moon did.
Mermaids seem to have an allergic reaction to a certain substance of aftershave, which cause their powers to blow uncontrollably when they sneeze.
Dangerous Coral
Mermaids, like other fish, have a reaction to a type of dangerous coral. If they get cut by it, toxin enters their body causing them to go on a feeding frenzy for sea food. Then their scales start to turn white, they grow gills on the neck, webs between their fingers and their hair starts to turn green. In "Fish Fever" Emma gets cut by the coral and goes through the changes, but is fortunately cured.
Trivia
Natural-born merpeople do not have a human form, although they have the ability to give themselves one. Although that kind of magic isn't possible without a powerful source of moonlight. So this can only be done with a Moon Ring or full moonlight itself. When natural-born merpeople first grow legs, they are naked.
It is possible that the amount of time it takes for the transformation to take full-effect can vary depending on the amount of water the merperson came into contact with. For example, if a bucket of water was dumped on a merperson's head or they dove into the ocean, they'd transform immediately. If a merperson came into contact with a normal amount of water (Such as spilling a glass of water one oneself) it would take the normal 10 seconds approx.
Merpeople can die from water deprivation. As mentioned by Sirena, merpeople have died from, "drying out". It is unknown if a human transformed by a Moon Pool would also have this effect as well.
Merpeople are mortals, like humans.
All the known characters that were born mermaids/mermen have blue eyes. This may be coincidental after the casting of the actors, or may serve as a fact that the full blooded merpeople always have blue eyes. The only exception is Zac.
All natural born merpeople love seafood. This is shown when Evie rather eats fruit than the lobster while all the other merpeople have never been shown eating anything else than seafood.
It was revealed in, Dolphin Tale that natural-born merpeople can speak the languages of sea creatures, as Sirena and Nixie can speak dolphin and Mimmi can speak humpback whale.
It is possible that only natural merpeople can make themselves invisible.
