Conservation scientists have identified eight "biodiversity hotspots" around Britain's coast which they say ought to be priorities for protection.
Protected areas could help to regenerate valuable fish stocks
The Marine Biological Association (MBA) and WWF want these areas to be given protected status under the government's proposed Marine Bill.
They include areas of importance for fish, mammals, birds and shellfish.
The government says it remains committed to introducing a Marine Bill within this term of Parliament.
Its absence from the Queen's Speech surprised and angered conservation groups. Publication of a white paper could come as early as March.
Currently, the UK has 56 Special Areas of Conservation (SACs) which include marine habitat, with a further five under consideration.
Development is restricted in these areas; but WWF believes hotspots need a higher level of protection, as has recently been implemented around the Isle of Lundy, the UK's first "no-take zone" where fishing is banned.
"It's part of our international commitments (on biodiversity), and if the government doesn't now come forward with the bill we will be immensely upset," said WWF's marine policy officer Kate Reeves.
"These are particularly diverse areas, and we want them to be highly protected marine reserves," she told the BBC News website.
With such a range of habitats around the coast, scientists need a way of identifying which ones should be priorities for protection.
The Marine Biological Association and partners have used a complex set of criteria. Broadly speaking, an area is considered special if:
- it includes a high proportion of the global or regional population of a species
- it is home to organisms that do not move
- decline has been identified
- decline is likely
- it is manageable as a coherent unit
They assessed more than 120 sites around the UK, and detailed eight areas which they feel are especially deserving of protection.
These include Plymouth Reefs in the southwest of England, Rathlin Island in Northern Ireland and the Menai Strait in Wales.
All are notable for a huge richness of species. Unst in the Shetlands contains the only British representatives of species that thrive in the Arctic, including some sea urchins and sea cucumbers.
The estuary of the Blackwater in Essex is important for wading birds, yet threatened by human development; while the Dogger Bank in the North Sea is important for the harbour porpoise and as a spawning ground for herring.
The government acknowledged the need for marine protected areas in the consultation which it ran last year on the scheduled Marine Bill.
Protection can have benefits for people as well as nature. The Isle of Lundy no-take zone has led to a significant rise in the number of lobsters, which could provide a boost to the local fishing industry.