The Reds confirmed Ferreira's departure at a press conference on Tuesday after the 25 year-old requested a release from his contract to ink a deal with the Mariners.
Ferreira scored 13 times in 54 games for Adelaide since joining the club in 2012 but the crowd favourite has not played since injuring his hamstring against Newcastle Jets on 19 December.
"Fabio has been a great player for our club but more importantly also a great person and we understand the reasons behind his request to terminate his contract," Adelaide United Chief Executive Officer Michael Petrillo said.
"Once we had this request we worked very hard and quickly to look for a suitable replacement and once we had secured the player we wanted, we agreed to release Fabio from the remainder of his contract."
Ferreira's departure opened the door for coach Josep Gombau to secure the services of Spanish attacker Miguel Palanca, who played three times for Real Madrid after joining the Bernabue giant in 2008.
The 27 year-old joined Elche - then in the second tier - in 2010 before moving on to Numancia in 2013.
Palanca played his youth football with Reds midfielder Isaias Sanchez and joins the club until the end of the season.
"We are trying to play this particular style and to bring a player like Palanca will only help us improve as a team," Reds coach Josep Gombau said.
Meanwhile, Mariners coach Phil Moss was glowing in his praise of his new recruit.
"I am delighted to have secured the signature of a player I believe is one of the top wingers in the Hyundai A-League," he said.
"Fabio is an excitement machine, possesses genuine pace, and has a very strong record in the competition in terms of goals and assists.
"He is also a player of fantastic character, a player who puts the team's aims ahead of his personal ambitions.
"That is one of the reasons why he has been a fan favourite in Adelaide and we're sure he will become a fan favourite during his time with us."
"With the right application we're sure Fabio will have a real impact for us in the back half of this season, and during our 2015 AFC Champions League campaign."
