"After 11 league games we find ourselves a long way away from where we expect to be," said CEO Ryan Sparks.
"As a result, the decision has been taken to move in a different direction in an effort to get our season on track.
"On a personal level, I have very much enjoyed working alongside Mark and [assistant manager] Glyn [Hodges], and we go our separate ways on good terms.
"Unfortunately, since our defeat at Carlisle in the play-off semi-final, results have been disappointing."
Kevin McDonald has been named interim player-manager.