The goal was no more than the Shrimps deserved following their first-half pressure and Mullin wasted a glorious chance to make it 2-0 five minutes after the break when he headed against the crossbar.
Grimsby made the most of their let-off with Coulson firing past Barry Roche in the 59th minute.
The Mariners looked the more lively side thereafter and Michael Leary forced Roche into a decent block late on.
Source: Team Talk
Source: Team Talk