Two Welsh coastguard centres which were threatened with closure have won a reprieve.
Milford Haven and Holyhead stations will stay open but Swansea, which was to be downgraded under the plans, is now to close by 2015.
Eleven centres across the UK will now remain open, all operating around the UK.
The Welsh Government said UK ministers would have to "account for any consequences" for sea safety.
Shadow Welsh Secretary Peter Hain said the UK government should "U-turn" on its Swansea decision as it had done on the one for Holyhead and Milford Haven.
Campaigns to save Milford Haven and Holyhead stations saw a 20,000 name petition go to Downing Street.
The two reprieved stations were to shut, with Swansea reduced to operating only during daylight hours.
But the strong local protests, including lobbying the chief executive of the coastguard service when he visited Milford Haven in February, sparked the policy change.
Campaigners argued that as well as watching over the UK's third largest port, the Milford Haven centre also watched over the coastline from Carmarthen to Barmouth, an area which is typically very busy with tourists and leisure craft.
Swansea, which has 28 personnel, is now one of eight coastguard stations which will undergo phased closures between 2012 and 2015.
The details were revealed in a Commons statement by Transport Secretary Philip Hammond, who said that Holyhead was being favoured instead of the MCA base at Liverpool following representations over Welsh language concerns.
He said Swansea was being closed instead of Milford Haven in Pembrokeshire due to the higher level of government employment in the city.
Plaid Cymru MP for Carmarthen West and Dinefwr Jonathan Edwards described the announcement as "bittersweet".
He said: "Milford Haven and Holyhead have fought fierce battles to be kept open and we welcome the announcement that they will remain fully operational.
"But there are now huge questions as to why exactly Swansea is to be closed? I will be asking what representations were made by ministers from the new Welsh government on this?"
Dennis O'Connor of the Save Milford Campaign which handed over a 20,000-name petition said he was "delighted".
But he described the news that Swansea would close as "devastating".
"We will do everything we possibly can as a campaign group to offer our support to Swansea and the other coast guard stations threatened in the UK," he said.
Preseli Pembrokeshire MP Stephen Crabb said: "This is fantastic news and exactly what we have been working for.
"The minister always said this would be a genuine consultation and that he would modify the proposals if necessary. He has done just that."
Lib Dem MP for Ceredigion Mark Williams said: "This is very good news, which shows a welcome willingness to listen to the concerns that were expressed at the original proposals.
Anglesey MP Albert Owen, who campaigned to save Holyhead, said: "We put a strong case together based on irrefutable facts; local experience, knowledge and skills; a knowledge of the Welsh language and the strategic importance of Holyhead.
"However, the campaign is not over, there will be a six week period of consultation, therefore we must keep the pressure up, moving forward with our vision to provide safer coastlines for all."
A Welsh Government spokesman said: "We will be seeking urgent assurances from the UK government that they have considered all the potential risks of closing such a strategically important station.
"The UK government will need to account for any consequences this decision may have on the safety of shipping and other people using the coastline."