Grimsby, with only two league wins all season, lie just above the bottom two as much to the incompetence of Wrexham and Lincoln as anything they have done themselves.
The Mariners, in front of a bumper crowd, were embarrassed by Football League newcomers Morecambe who were bright and breezy and full value for the points.
Grimsby have now gone eight league games without a win and this was Morecambe's first League Two success since mid-October.
With a painfully thin squad Grimsby are losing players through injury and suspension and their disciplinary record is absolutely shocking.
Midfielder Danny Boshell became the latest player to be red-carded and with his 75th minute dismissal ended Town's hopes of a point.
They presented Morecambe with a two-goal lead by the 49th minute and though sub Andy Taylor showed great striking instinct to snaffle up a backpass and tip it into the bottom corner, the Mariners could not pull things round.
Morecambe had gone ahead on 27 minutes when striker Jon Newby beat keeper Phil Barnes with a delightful chip from the edge of the box.
What Grimsby wanted was a good start to the second half and although they started brightly, they were rocked back on their heels when a left-wing cross enabled the unmarked Michael Twiss to head past Barnes, who got a hand to the ball but could not keep it out of the net.
Grimsby's immediate reply gave them some hope, but even with limited attacks Morecambe managed to look more dangerous and Twiss looked to have beaten Barnes again, only for the keeper to desperately grab the ball back when it appeared to have gone over the line.