The shingle beaches that fringe much of the British coast are threatened by development pressures, conservationists say.
By Alex Kirby
BBC News Online environment correspondent
They are concerned chiefly for the few large beaches able to support vegetation.
Dungeness nuclear power station sits on the beach
These form a unique habitat which is home to a range of rare insects and plants, and to several seabird species.
The beaches also often serve as an effective natural form of flood defence.
The alert is sounded by English Nature, the government's wildlife advisers, in guidelines published to promote the conservation and restoration of vegetated shingle.
This is defined as beaches with sediments between two and 200 millimetres in diameter deposited above the high water mark, which can be colonised by specialist vegetation adapted to the harsh, dry and salty conditions.
Plants typically found on shingle beaches include the bright yellow biting stonecrop, the purple and yellow bittersweet, red valerian, and sea holly.
A range of spiders, bees and other insects also lives there, and the beaches are important for breeding birds including gulls, waders and terns.
English Nature calls them "stony deserts", because the stones heat up by day and cool significantly at night, and because their free-draining nature creates conditions like a desert.
It says these dynamic structures, which are continually losing and gaining pebbles, can serve as natural flood defences which absorb the sea's energy.
Yet industry, power stations, housing and coastal defences have encroached on the shingle, which is often also used for building material.
English Nature says the greatest threats to the shingle are coastal defence works, sea-level rise, pressure from recreational uses like walkers and off-road drivers, and the invasion of alien plants escaping from dumped garden waste.
Sea kale, scientifically Crambe maritima
England has a significant proportion of the European total of vegetated shingle with about 4,350 hectares (10,750 acres), five times more than the rest of the UK.
Very few areas support vegetation, because most of the smaller beaches suffer too much disturbance by winds and waves.
The largest shingle beach (about 1,600 ha, 3,950 acres) is at Dungeness in Kent, made up of Ice Age flint. Only five other beaches are larger than 100 ha (250 acres).
Most are in eastern England and along the Channel coast, with some others found in northwest England.
There are 26 shingle sites of special scientific interest (SSSIs, the highest UK conservation category). Almost half are in poor and declining condition.
Mertensia maritima, the oyster plant
Dr Roland Randall, of Cambridge University, co-author of the English Nature report, told BBC News Online: "Shingle beaches are important to vegetation and invertebrate scientists for the creatures that live on them.
"They're important to people who enjoy the flowers and birds they shelter, and they're very important economically.
"They matter very much economically, not just as natural defences against the sea, but because you get deep water immediately offshore.
"That's how nuclear power stations on the coast get their cooling water, and if there's erosion then they can have problems.
"They're sometimes important locally. In the massive drought of 1555 people survived by eating the sea peas growing on a shingle beach, at Orfordness in East Anglia. Without them they would have died."
Images courtesy of English Nature