Britain's seas are in crisis, with key species in serious decline, according to conservationists.
Deep water mud habitats found in sea lochs are under threat
A report by the WWF blames inadequate planning and poor management.
The Marine Health Check report says 13 of the 16 species and habitats investigated are in decline, including reefs and salt marshes.
The majority of damage to marine habitats is due to coastal development, fishing, aquaculture and oil and gas exploitation, claims the WWF.
The report, which was written by the Marine Life Information Network at the Marine Biological Association of the UK, follows a survey five years ago into the state of Britain's seas.
The study carried out in 2000 warned of many potential threats to aquatic wildlife, such as sand and gravel extraction in pristine areas of the seabed.
According to the WWF, these threats have now become a reality, adding to longer-term pressures such as pollution and invasion by non-native species.
WWF Senior Marine Policy Officer, Jan Brown, told BBC News: "We've got habitats from deep sea mud to salt marsh and sea grass beds... They are all in serious decline at the moment because we are just not managing our seas properly.
"We are putting a lot of pressure on our seas in terms of development... You've got oil and gas, aggregate extraction and now offshore wind development. They are not being planned together with nature conservation as they would be on the land.
"If nothing is done our children's children will be faced with a very sad, degraded sea and an unhealthy sea.
"It's not only fishing we are now discovering there are plantsin our seas with medicinal properties so it's a bit like destroying the rainforest before you know what you've actually got there."
The majority of damage to marine habitats is due to bottom trawling and dredging, Dr Brown says.
Horse mussel beds, for example, house about 100 other species, but they are being destroyed by scallop dredging.
Surveys carried out in Strangford Loch, Northern Ireland, have shown a 3.7 km sq loss of these beds since 1993.
Deep water mud habitats found in sea lochs are heavily targeted for scampi. Although some areas, such as Loch Torridon, have received increased protection, others have continued to be trawled.
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The UK's marine legislation has been developed on a sector by sector basis. According to the WWF this has led to a disjointed management of the marine environment.
They want an ecosystem approach to marine management to be at the heart of the government's forthcoming Marine Policy Bill.
The Royal Society for the Protection of Birds' (RSPB) Marine Policy Unit agrees that marine protection is of paramount importance.
"We have half of our biodiversity in the seas, so it is an incredibly important part of our natural history," RSPB spokesman Graham Madge told the BBC News website.
"But around the UK less than a handful of marine sites receive protection - they really are seen as the Cinderella of conservation."