The free agent pool continues to fill up with veterans prior to the market opening on March 10.
Hartline was due $5.9 million in 2015. The move saves Miami $3.15 million against the salary cap. The 28-year-old signed a five-year, $30.775 million contract in 2013.
Gibson signed a three-year $9.755 million contract that same offseason. His release will save the franchise $3.26 million.
Hartline's role diminished in 2014 with the emergence of Jarvis Landry. The vet caught just 39 passes for 474 yards and two touchdowns. His production as a No. 3 or 4 receiver did not match his high salary.
Gibson was a No. 4 receiver who caught 29 passes and one touchdown in just 516 snaps.
At the right price, Hartline can still provide value to a team looking to add depth. Gibson would remain a low-level option for a receiver-needy team who might have to battle to make a roster.