Nearly 150,000 rare seabirds, including the little tern and black-throated diver will benefit from moves to expand the Blue Belt, which is made up of classified Special Protection Areas (SPAs).
The latest expansion will add a 24-mile stretch of coastline between Falmouth Bay and St Austell Bay in Cornwall to the Blue Belt, which already protects 23% of UK waters, and more than 300 sites across land.
The move is intended to protect populations of rare, vulnerable and migratory birds.
This latest expansion targets the UK’s most important site for the wintering black-throated diver.
The designations will help to safeguard the feeding grounds for little terns, Sandwich terns, and common terns, which are all amber-listed due to declines in the size or range of their breeding populations.
It will also cover the habitats frequented by the great northern diver and Eurasian spoonbill.
The latest designation, at 650 square miles, covers an area equivalent to 55,000 football pitches.
It is intended to help minimise disturbance to the feeding areas and marine habitats the black throated diver relies on and to provide a safe haven for them during winter.
Environment Minister Therese Coffey cited BBC1’s popular environmental series in the ongoing efforts to expand the Blue Belt.
“Like the millions of others watching Blue Planet II, I am only too aware of the importance of protecting our precious marine environment, and the wildlife that relies on healthy and productive seas.”
A further marine SPA has also been announced in the Irish Sea between the Isle of Man and Anglesey, home to the largest known aggregation of Manx shearwaters, which can number at up to 12,000 in the area.
Natural England chairman Andrew Sells said extending the Blue Belt was a vital measure to protect the UK’s wildlife that would help them “thrive into the future”.
“Terns and Manx shearwaters, with their dramatic aerial displays, are a magnificent sight above our seas.”