Cleo works at an oceanic center rather than a marine park. With marine parks falling out of favour, this is rather logical.
Mr. Setori is a member of the coastguard rather than a fisherman.
Zane's father is strictly a businessman rather than a doctor and a businessman.
Adaptational Nationality: Possibly. Due to Stanley Finch having found an Aztec mask in the area, it is possible the characters live in California instead of Australia, though the map shown in The White Mermaid is a better approximation of the southern coast of Australia than the Californian coast.
The girls can now breathe and speak underwater, as they no longer have the limitations of a live-action actress.
The full moon no longer hypnotizes them, but their powers do go out of control if they use them under a full moon.
Alliterative Name: In the case of Cathy who becomes Cathy Chadwick upon marrying Terry, Rikki's father.
All There in the Manual: The series bible give Emma's star sign as Capricorn, Cleo's as Pisces and Rikki's as Leo. This is the closest we get to an idea of who in the trio is the oldest and who is the youngest, but it invites ambiguity. Due to the Capricorn's area of birth spanning from December 21st to January 21st, this means Emma is either the oldest or the youngest of the group. With the former, it means Cleo is in the middle and Rikki is the youngest, while with the latter, it means Cleo is the oldest and Rikki is in the middle. Lewis' star sign is also identified as Cancer, making him a few months younger than Cleo.
Alpha Bitch: Miriam is rude, snobby, ungrateful and bitter just like her live-action counterpart.
Animesque: The show's art style. It basically looks like an anime cartoon but in the modern flash style.
Bloodless Carnage: A minor aversion in "Jaws-ache" where Berk's broken tooth is removed and some blood is shown in the water. A less minor one appears in "A Strange Phenomenon" where Cleo has a rather large cut on her hand and blood is clearly visible.
Cassandra Truth: In "Reported Missing", Kim discovers that Cleo, Rikki and Emma are mermaids via reading Cleo's diary. When she tells her parents, they don't believe her. When Kim tells Emma's brother Elliot he doesn't believe her either but she talks him into proving it with her.
The Cavalry: The sea life serves this purpose during the climax of "The White Mermaid."
Color-Coded for Your Convenience: The girls all have a different coloured tail as mermaids: violet for Cleo, red for Rikki and orange for Emma.
Combat Tentacles: Danny the octopus employs his tentacles for fighting one some occasions, the first instance being the first episode.
Continuity Nod: "The Creature from the Bay" features Danny the Octopus claiming that he is a star again upon seeing underwater photographers to which he is told that no one is interested in a has-been octopus, all referencing the episode "Dolphin City Mascot."
Crying Wolf: As a result of too many pranks, Teddy the sea turtle is not believed when he tells the other sea creatures and the mermaids about an undersea volcano that is going to erupt soon in "Imminent Danger", at least until the mermaids actually do look at it.
Rikki gets trapped in a net in the episode "Caught in a Net" when explaining to Teddy the sea turtle why he should trust the humans from the oceanic center.
Cleo gets captured by treasure hunters looking for the sunken ship the White Mermaid. First chance she gets she throws herself into the sea.
Death by Adaptation: Rikki's mother is established to have died during her daughter's childhood rather than being divorced from Rikki's father.
Decomposite Character: Rather than Cleo being the one to have a stepmother, it is Rikki this time around who gets one. Considering that Terry was established as being divorced in the original series from the first mention of him and that he is established as having been a widower here before meeting Cathy, it just makes more sense.
Department of Redundancy Department: In "Valentine's Day", Lewis refers to the girls as "spies, backstabbers, traitors" when he finds they've been following him and Abby around. "Backstabber" and "traitor" are synonyms.
Disabled in the Adaptation: In contrast to his live-action counterpart who only wore the glasses on a few occasions, this version of Lewis wears them all the time.
Dumb Muscle: Burk the hammerhead of the Vandals isn't quite the brightest pearl in the sea.
Early-Installment Weirdness: In the costume department, Emma's bikini bottom is completely different in the first episode with it sharing the pattern of her top, rather than the pattern belonging to a cover-up and the bottom being completely dark blue.
Fall Guy: Or "Fall Girl" in this case. Miriam turns Rikki into one in "Underwater Takeover" by stealing her phone and using it to call the fire department that there was a fire at their school, which there wasn't. Miriam then plants the phone back in Rikki's bag, post-fire department's arrival, and when the call is traced back to her the belief is she is the one that called the false alarm. Miriam's reason? There was a test that would cause her to miss a big sale.
Fangirl: Rikki shows some minor cases of being one in "Poseidon's Daughter" when she says she'd jump into actor Brad Passive's car. Cleo showed similar cases, such as squeeing to Lewis when Brad's co-star Scarlet Belladonna spoke to her.
Fanservice: A show set in (presumably) Australia with the three leads being attractive teenaged girls and there are many scenes set at the beach. Girls in swimsuits are common in this show. Cleo wears a one-piece, a bikini on one occasion and Rikki and Emma both wear bikinis.
Freezing on Lewis' laptop in The White Mermaid reveals Mako Island to be south of Dolphin City and east of a fictional Jacky Bay.
A scene in "Dolphin City Triangle" featuring the local newspaper that Abby shows Lewis and the girls has the story "local Irish Band Celebrates St. Patrick's Day with Military Men and Women Overseas."
A scene in "Bad Waves" shows the names of other girls on Lewis' contact list as being Christine, Isa, Juliette, Karine, Megane, Juju and Carole.
A scene in "Valentine's Day" features Abby's blurb about herself on her blog saying: "I am a freelance journalist since 2010. Previously, I practiced my profession in newspapers, first The Student, where I led the service including (...)". This frame indicates that the show is set post-2010 and provides a little bit of information on the past of a secondary character. The frame also reveals that Abby has written a book.
"The Return of the White Mermaid" has a scene during Cynthia's birthday showing her cake, which has fifteen candles on it.
In "Kidnapped", the raffle tickets give the date as August 2014.
Gold Digger: Not really but Rikki fears her future stepmother is one in "The Lost Ring."
Goldfish Poop Gang: The Vandals are as incompetent as they get when you think an eel, an octopus and a hammerhead shark would be quite formidable.
Gossip Evolution: "It's in the Bag" features Rikki saving Ziggy the Clown Fish after a shell fell onto him. He goes on to tell the other sea life how he was afraid it had been a shark or an octopus and sure enough later tellings of the story have it be either of those two and the final being both.
Graceful Ladies Like Purple: Cleo's one-piece and her rain coat and hat are all violet, a shade of purple. Even her bracelets and coral top in her mermaid form are a shade of purple. The series bible even identifies her favourite colour as violet, the same colour as her tail.
Grumpy Old Man: Well, the words used by Carlotta the jellyfish were "cranky old crab" to describe Bernie the hermit crab in "Handle with Care" but he neither likes Carlotta singing outside his cave nor Teddy the sea turtle and his clown fish friends playing outside it.
Hair Color Dissonance: Cleo's family has purple hair, but Cleo is referred to as brunette or black-haired depending on the person, possibly meaning it is intended to be a very dark brown.
In "The Mysterious Seaweed" a picture of Boris Karloff as Frankenstein's Monster can be seen in Zane's locker. Apparently he is a fan of classic horror films.
In "The Lost Ring" Rikki shows interest in a comic book implying she might have an interest in such things.
"Reported Missing" features Cleo watching a news story on the latest motifs for swimsuits, implying an interest in fashion. The same episode also features a drawing from her journal, showing a rather animesque style of drawing for her.
Hong Kong Dub: With the animation having been done in Germany, with the lip-sync meant for German, this is the end result.
I Need to Go Iron My Dog: In one episode, Byron abruptly leaves a conversation with Cleo upon Emma's arrival saying that he is late for his guitar lesson. Besides Emma's obvious bafflement at the abruptness at her departure, there is also the implication that Byron doesn't even take guitar lessons.
Laser-Guided Amnesia: One episode features Cleo losing all memory of being a mermaid, and hijinks ensuing while Rikki and Emma try to get her to not accidentally blow their cover.
Mermanity Ensues: Much like in the live-action series, the girls are transformed into mermaids after going into a strange pool on Mako Island during a full moon.
My God, What Have I Done?: Rikki in "The Lost Ring" when she realized that the woman who will become her future stepmother isn't the gold digger as she thought of and that she ruined her father's attempt to connect with her for no reason other than a misunderstanding.
Naked People Are Funny: Or rather crabs. When the toy car that is Bernie's shell gets stolen by an octopus, Teddy gets a good laugh upon seeing him.
No Dress Code: Heavily downplayed, as it is only shown with Emma, who wears a midriff-baring top, something a real life school wouldn't allow.
Noodle Incident: "Underwater Takeover" has revealed that Lewis once asked the school to build a particle accelerator. No, we are never told why, only that the school could not afford to.
Oh, Crap!: Emma has a moment in "Trapped" when her brother Elliott has stolen her phone, which has personal things on it. It gets worse when Elliott shows the phone to Zane who finds a particular video on it that he makes viral and Emma the laughingstock of their school.
Oh, My Gods!: Bernie exclaims "in the name of Poseidon" in "Handle with Care" when he gets aggravated by Carlotta's singing, and later when he's trying to get the Vandals out of his cave.
Orichalcum: the magic crystals in "Dolphin City Triangle".
Out-of-Context Eavesdropping: "The Lost Ring" and "Valentine's Day" respectively have Rikki and Cleo misinterpreting what their loved ones were talking to another person, and so they try to take action which resulted in dire consequences.
Pink Means Feminine: Downplayed, but Rikki's sleepshirt and raincoat and hat are all pink. Her scrunchie is pink too, but is so pale a shade you might mistake it for something else. Even her headband, seashell top and bracelets in her mermaid form are a shade of pink. The series bible refers to her favourite colour as scarlet red and taking pink's relation to the colour red, her wearing of pink makes sense.
Red Oni, Blue Oni: The trio: Rikki is the feisty, spunky and Badass Adorable red oni (who is an ironic Fiery Redhead) and Cleo is a sensitive, timid and Shrinking Violet blue oni. Emma balances between the two being the blue to Rikki and the red to Cleo.
Seashell Bra: Rikki has one as a mermaid in contrast to Emma and Cleo who have, stars and coral respectively, and even more in contrast to the usual seashell bra in animation where it is literally just two shells placed on her breasts with no strap or anything.
Setting Update: The show is set in 2014 and while it might still be set in Australia, it is possible it was set somewhere in California, due to the mentioning of an Aztec treasure being nearby or something along those lines and no text being in Spanish.
Shapeshifter Mode Lock: Two different episodes feature both flavors; one where Emma is stuck as a human, and another where Rikki is stuck as a mermaid.
In "Dolphin City Mascot" Abby says that Danny will be more famous than Lady Gaga in regards to Danny's predictions of sporting events.
While the plot is completely different, the in-universe film "Poseidon's Daughter" is clearly named after Neptune's Daughter.
Shown Their Work: In "Jaws-ache", Cleo correctly states that only five types of sharks are dangerous. The only dangerous one she mentions is the Great White, with unmentioned other four being the Tiger, the Blue, the Oceanic Whitetip and the Bull, in truth the most dangerous of the five due to being able to survive in fresh water.
Show Within a Show: Or rather "film within a show." The episode "Poseidon's Daughter" features a film of the same name being filmed with actors Scarlet Belladonna and Brad Passive as the romantic leads and the plot being about a fisherman and a mermaid who saves him from drowning.
Significant Green-Eyed Redhead: Inverted in that the two individuals with green eyes and red hair are rather minor, unnamed characters. Also averted with Rikki, who is a redhead with reddish-brown eyes, proving you don't need green eyes to be a significant redhead.
A literal example due to Danny being an octopus as Cleo finds out when rescuing him from the oceanic centre in "Dolphin City Mascot."
A straight example involving a different octopus that has stolen many an object out of boredom in "The Lost Ring."
Stock Ness Monster: "The Creature in the Bay" features Rikki being mistaken for one when her tail is spotted splashing at the surface by Emma's brother Elliot and the Loch Ness Monster is mentioned in the episode as well.
Stunt Double: In "Poseidon's Daughter", Cleo fills in for Scarlet Belladonna after the latter gets too seasick to film her own mermaid stunts. Luckily, only one member of the film crew figured out that Cleo didn't use the mermaid tail provided for her, but he keeps quiet.
Talk Like a Pirate: Apparently pirate captain Edward the Cruel spoke like this as indicated in "The Return of the White Mermaid" when the Stone Circle swaps his soul with archaeologist Stanley Finch's.
Happens to Cleo and Emma in due part to a bored octopus in "The Lost Ring."
Danny does actually employ his tentacles in such a fashion against Cleo in "Underwater Takeover."
The Prankster: Teddy the Sea Turtle becomes one out of boredom in "Robot Duel." He is at it again in "Imminent Danger" until it results in Crying Wolf for him.
Tomboy with a Girly Streak: A minor example but Rikki is shown admiring a pearl necklace in "Kidnapped!" A less minor case with her would be her pale pink scrunchie, her pink sleep shirt and her pink rain coat and hat. When coming up with an excuse as to why she can't go to Byron's birthday party, she says she has a babysitting job. True, it is an excuse, but logically she wouldn't have used it if she didn't actually babysit, which is traditionally feminine.
Total Eclipse of the Plot: While the eclipse does not occur the whole way through of "Imminent Danger", Cleo glimpsing a lunar eclipse is what causes her to lose her powers for the episode.
Troubled Fetal Position: Rikki goes into this in "Three Days Underwater" after realizing she can't turn back into a human courtesy of a spell and that her father forgot her deceased biological mother's birthday.
True Blue Femininity: Heavily downplayed. In contrast to Cleo and Rikki with the colours purple and pink, Emma's use of the three feminine colours is restricted solely to her bikini. Even the series bible identifies her favourite colour as orange, making her stand out among the three mermaids.
Use Your Head: Berk actually uses his head to break some underwater crystals in "Dolphin City Triangle." In the later episode "Imminent Danger" he uses his head to drive nails into a sunken ship that will be used for shelter in the event of a possible tidal wave.
What the Hell, Hero?: Rikki and Emma give Cleo a brief one in "Valentine's Day" when she actually uses her powers to splash Abby, who is on a gondola ride with Lewis, on a clear day risking her finding out about them being mermaids.
World of Technicolor Hair: Heavily downplayed, as most characters have normal coloured hair and the Setori family is an example of Hair Color Dissonance, but Miriam's dull pink hair and Abby's dark blue hair is never identified as dissonance, meaning there are just two named individuals with abnormal hair colours.
You Watch Too Much X: Mr. Sertori's reaction to Kim telling him and Mrs. Sertori that Cleo is a mermaid.
Stunt Double: In "Poseidon's Daughter", Cleo fills in for Scarlet Belladonna after the latter gets too seasick to film her own mermaid stunts. Luckily, only one member of the film crew figured out that Cleo didn't use the mermaid tail provided for her, but he keeps quiet.