The striker has opted to reject a new contract with the Shrimps, instead signing for League Two rivals Forest Green Rovers.
Collins arrived at the Globe Arena in the January transfer window after being released by Wolverhampton Wanderers.
He signed a deal until the end of the season and scored eight times in 15 appearances.
Boss Jim Bentley was keen to tie him down to a new deal
Bentley said: “We were desperate to keep Aaron as we rate him very highly.
“We’ve tried to sign him a few times in the past and the chance came about at the end of the January transfer window and he had a fantastic few months in a Morecambe shirt, scoring some very important goals.
“We will always be very grateful for his contribution.
“We tried our very best to keep him at the club but unfortunately for us, it wasn’t to be.
“I like Aaron as a player and a person and I’m sure everyone connected with the club would like to wish him the very best of luck for the future at his new club.”
Meanwhile veteran forward, Kevin Ellison has signed a new one-year contract.
It will be the 21st season in professional football for the 40-year-old ace, who has played in the Premier League.
“If you would have said to me at 21 that I would get 10 years as a pro I would have snapped your hand off but I’ve looked after myself and Í’m delighted to still be playing and making an impact at my age," he said.
“Not many people have played into their 40s and I don’t think many will so it is something to be proud about.
Shrimps’ boss Jim Bentley said Ellison still had a “lot to offer’’.
He said: “Kev is part of the furniture at Morecambe FC and is a big character who us much loved by the fans"