Seagrass destruction revealed

Posted: 14 October 2003

Manatees, dugongs and green sea turtles are just some of the growing list of already threatened species at risk from the destruction of ocean seagrass, a new report has revealed.

The first global survey of the underwater meadows of seagrass that skirt the world's coasts reveals that 15 per cent of this unique marine ecosystem has been lost in the last 10 years.

Green turtle in seagrass
Green turtle in seagrass
The seagrass beds in the Gulf are home to the World's second largest group of endangered dugong and significant populations of herbivorous green turtles.© Alex Stewart/UNEP

The findings give new urgency to protect and conserve these important habitats, which are threatened by runoff of nutrients and sediments from human activities on land, boating, land reclamation and other construction in the coastal zone, dredge-and-fill activities and destructive fisheries practices.

The World Atlas of Seagrasses, prepared by the UN Environment Programme World Conservation Monitoring Centre (UNEP-WCMC) provides thefirst ever global estimate for seagrasses world-wide: 177,000 sq km, an area just two thirds the size of the UK.

Hard facts

"We now have a global, scientific view of where seagrasses occur and what is happening to them," said Klaus Toepfer, UNEP Executive Director.

"Unfortunately, the scientists have presented us with a worrying story. In many cases, these vitally important undersea meadows are being needlessly destroyed for short-term gain without a true understanding of their significance."

"The World Summit on Sustainable Development adopted, in the area of biodiversity, a commitment to reverse the trend of losses by 2010," said Toepfer. "To achieve this we need hard facts on which to base decisions. The World Atlas of Seagrasses meets that need for a vital marine ecosystem whose importance has largely been overlooked until now."

Seagrasses are a mixed group of true flowering plants - not seaweed - that grow submerged in large meadows in both tropical and temperate seas.

Sixty species

They are a functional group of about 60 species of underwater marine flowering plants. Thousands more associated marine plant and animal species use seagrass habitat. They range from the strap-like blades of eelgrass in the Sea of Japan, at more than 4 metres long, to the tiny, 2-3 cm, rounded leaves of sea vine in the deep tropical waters of Brazil.

Seagrass Australia
Seagrass, Australia
Posidonia Australis fruit meadow. Australia Seagrass Watch has shown that even following acute impact, seagrass meadows can recover within 3 years if protected and managed effectively.D. Walker/UNEP
"Seagrasses are quite possibly the most widespread shallow marine ecosystems in the world." Yet, says Ed Green, one of the co-editors of the Atlas, "there are few places where seagrass meadows are protected.

"The importance of seagrass has not previously been recognised," he said.

"By pulling together the work of researchers worldwide we now know that vast numbers of fish use seagrass for a short but critical part of their lifecycle. We are also becoming aware of the role that seagrass plays in the climatic and oceanic carbon cycles and in coastal protection. The true economic value is difficult to measure but this work suggests it is immense."

Sea horses

According to the new UNEP-WCMC Atlas seagrass meadows should be considered one of the most important shallow marine ecosystems to humans, playing a vital role in fisheries, protecting coral reefs by binding sediments, cleaning coastal waters and providing coastal defence from erosion.

"Seagrass beds have been needlessly destroyed for short-term gain without real analysis of the values that the intact ecosystems bring to coastalsociety," said Mark Collins, Director of UNEP-WCMC.

"Physically they protect coastlines from the erosive impact of waves and tides, chemicallythey play a key role in nutrient cycles for fisheries and biologically they provide habitat for fish, shellfish and priority ecotourism icons like the dugong, manatee and green turtle. And yet, despite these important attributes, they have been overlooked by conservationists and coastal development planners throughout their range. The Atlas provides important material towards a much-needed Global Marine Assessment, another key objective of the WSSD."

"The public can play an important role. By insisting on protection for sea horses, turtles and dugongs they will also safeguard the ecosystem that supports them and has intrinsic benefits that are less obvious,' concludesCollins.

Under-estimate

The new UNEP-WCMC World Atlas of Seagrasses is literally putting seagrass beds on to the map for the first time. Fifty-eight authors were involved in writing the chapters and completely new data sets have been created, with records compiled from 520 sources and 120 countries.

However, the new global figure for seagrass is likely to be an under-estimate as seagrasses off the western coasts of Africa and South America remain unsurveyed.

The World Atlas of Seagrasses is available from: the University of California Press.For more information about the Atlas, including maps and photographs go to UNEP