At risk: a vital terrain that feeds the ocean's most fragile creatures

They are the meadows of the sea, beautiful and bountiful, feeding and sheltering some of the world's most endangered marine species.

They are the meadows of the sea, beautiful and bountiful, feeding and sheltering some of the world's most endangered marine species.

In the seagrasses that hug many of the world's coastlines, dugongs and manatees, green turtles and seahorses find refuge and rich pickings.

But survey of seagrasses has revealed that 15 per cent of this unique marine ecosystem has been lost in the past decade. Conservationists hope the findings will act as an alarm call to governments and policy makers to prevent further losses.

Seagrass beds are being destroyed by nutrient enrichment from human sewage, intensive fishing and even by yachting and jet-skiing, the editors of the World Atlas of Seagrasses say.

The atlas was produced by the Cambridge-based World Conservation Monitoring Centre (WCMC), in conjunction with the United Nations Environment Programme.

Dr Ed Green of the WCMC and Professor Fred Short, of the University of New Hampshire, pointed out at the launch of the atlas yesterday that unlike coral reefs and mangrove swamps - two associated habitats which are well known and at least in some cases, protected - seagrass beds are largely taken for granted.

"Seagrasses are possibly the most widespread shallow marine ecosystems in the world, yet there are few places where seagrass meadow are protected," Dr Green said.

Professor Short added: "Like coral reefs, seagrasses are at a critical juncture, heavily impacted by human activities and climate change."

The atlas, the work of more than 50 authors, provides the first estimate of seagrasses worldwide - 110,000 square miles, an area two-thirds the size of the UK.

It suggests that seagrass meadows should be considered one of the most important marine ecosystems for humans, playing a vital role in fisheries, protecting coral reefs by binding sediments, cleaning coastal waters and providing coastal defence from erosion.

They are vital habitats for sirenians - dugongs and manatees, the odd-looking sea cows which were once mistaken for mermaids. Sirenians are the only true marine mammal herbivores and seagrass beds are essential for their survival. Green turtles, one of the most endangered of the world's seven marine turtle species, are also highly dependent on seagrass.

Seagrasses are lovely to look at, waving in the current like cornfields in an underwater wind, and are a mixed group of about 60 species of true flowering plants (not seaweed) which reproduce sexually and produce pollen.

Thousands of other plant and marine animal species utilise the seagrass habitat, which ranges from strap-like blades of eelgrass in the Sea of Japan to the tiny leaves of sea vine in the deep. Seagrasses grow in large meadows in both tropical and temperate seas. Most are found in the tropics where they can be enormously important as shallow-water fisheries for coastal communities. But seagrass beds can also be found around much of the British coastline, particularly at Salcombe and Torquay in Devon, in Plymouth Sound and at Looe in Cornwall.

Two species of seahorse, the long-snouted ( Hippocampus guttulatus) and the short-snouted ( Hippocampus hippo- campus), are occasionally seen in British seagrass beds, along with shellfish, cuttlefish, pipefish and sea bream.

Examples of seagrass species can be seen at the National Marine Aquarium in Plymouth.