Image: Oyster mat used for restoration
Anne Birch  /  The Nature Conservancy
This "oyster mat" was one of hundreds planted at Indian River Lagoon in Florida as part of a recent restoration effort.
updated 5/21/2009 4:41:05 PM ET 2009-05-21T20:41:05

Granted, oysters don't look very helpful, but nature's way of filtering water of pollutants is in crisis: Overfishing and unchecked coastal development have resulted in the disappearance of 85 percent of all oyster reefs, making them the most severely affected marine ecosystem in the world, according to a report released Thursday.

"Reefs are functionally extinct in many areas, particularly in North America, Australia and Europe, and no are no longer able to provide any of the ecosystem services that benefit people," The Nature Conservancy said in releasing the report.

It found that several reefs in China have also seen drastic declines over the past 30 years. Half of the shellfish populations in South America are under threat, while flat oysters have been virtually wiped out in Australia.

Native oyster reefs — essentially mountains of the bivalves cemented together — were once dominant features of many temperate estuaries around the world. Much as coral reefs are critical to marine habitats, the bivalve shellfish are vital to bays and estuaries, creating habitats for a variety of plants and animals, the report said.

Nature's filters
Oyster reefs provide important benefits by filtering water, providing food and habitat for fish, crabs and birds, and serving as natural coastal buffers from boat wakes, sea level rise and storms.

If you're sucking down a wild oyster, it most likely came from one of only five regions on the east coast of North America, and in most of these regions, oyster reefs are in poor condition, the report said.

"Centuries of intensive fisheries extraction exacerbated by more recent coastal degradation have put oyster reefs near or past the point of functional extinction worldwide," according to the report.

Mary Seddon, chair of the International Union for Conservation of Nature's Species Survival Commission Mollusk Specialist Group, said the demise of the oyster goes back centuries, so the study's findings were not unexpected.

"Certainly, 85 percent of areas that have oysters have had major degradation," said Seddon, who did not participate in the report.

Advice, examples offered
However, the report concluded these ecosystems could recover if measures are taken to reduce pollution and better manage the reefs. It also called for efforts to protect oyster reefs through international treaties and to reduce the introduction of shellfish species that spread disease.

It highlighted several regions that have made positive strides, including China's Laizhou Bay where river flows have been managed more sustainably, and a marine protected area was established in 2006.

Seddon said she believed creating a network of protected marine areas and maintaining water quality by limiting the amount of sediment flowing into estuaries were crucial to saving oysters.

"By putting protected areas in place and maintaining them, you are reducing the impact of further habitat degradation," she said. "You can't have exploitation."

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