Scottish Labour MP Katy Clark, who secured workforce details through a series of parliamentary questions, said the revelations raised "genuine concerns about maritime safety off the west coast of Scotland".
Ministers have confirmed that the Belfast maritime rescue co-ordination centre was staffed at below risk-assessed levels on 428 out of 730 shifts in 2013.
The Belfast station took over primary responsibility for the west coast of Scotland after the closure of the Greenock-based Clyde operational centre in 2012.
At the time the Maritime and Coastguard Agency (MCA) denied claims by critics that the shutdown would put lives at risk.
Ms Clark said "The appalling number of unsafely staffed shifts at MRCC Belfast throughout 2013 shows just how poorly thought out the decision to close MRCC Clyde was.
"It is deeply concerning."
She said that in September, the government claimed that the recruitment of new MCA staff would solve the problems and the number of understaffed shifts at Belfast dropped dramatically in October to 5 shifts out of 62.
The MCA said it now has a full complement of 22 staff at Belfast and was expecting three new members of staff to start soon.
A spokeswoman said: "Under the future structure, the introduction of the National Network as part of the modernisation of HM Coastguard will enable the National Maritime Operations Centre and all other centres to coordinate any incident."