The 20-year-old leaves the Withdean Stadium after finding the net only five times in 52 appearances for the Seagulls.
Boss Micky Adams told the club's official website: "We've come to an agreement over his contract and we thank him for his efforts and wish him well for the future.
"Joe needs to play some first-team football."
Gatting had loan spells with Woking and Bognor Regis during his time on the south coast.