This film features a dedication to the late Howard Ashman, who co-produced and co-wrote the songs from the original animated film. He also contributed some key scenes to the film's screenplay, including Sebastian's decision to help Ariel win the Prince's heart. This is the second Disney film to have a dedication to Ashman, after La Belle et la Bête (1991).
Ursula and Triton as siblings in this remake was cut from the 1989 animated film, but it was included in the 2007 Broadway musical of the film instead. In the musical, Triton had banished Ursula from his kingdom and disowned her as a sibling for practicing black magic, which is what motivates her actions in the Broadway musical.
Melissa McCarthy had no idea she could actually sing before production of this film. She was coached by vocal coach Eric Vetro to prepare for her role as Ursula, and did all of her own singing in the film.
Contrary to the animated film, Sebastian has the correct number of legs (ten including two pinchers). The animated Sebastian had eight (including the pinchers), because at that time that was much easier to animate.
According to costume designer Colleen Atwood, every merperson accessory "had to be from the sea. For King Triton, we were trying to figure out how to make his crown look like a crown but not like it was a crown from above the sea. I saw these really giant shark teeth in a magazine, and I was like 'Oh my god, we should make his crown out of shark teeth.'"
Jodi Benson: the original voice of Ariel in La Petite Sirène (1989), appears as the person who gives Ariel a "dinglehopper" (fork) during her and Prince Eric's tour of the market.