Effective conservation measures can help oyster reefs cover, the study says
Marine habitat loss is causing a decline in shellfish populations, which is having an adverse knock-on effect on sensitive ecosystems, a study suggests.
Described as the first global assessment of its kind, it warns that 85% of the world's oyster reefs have already been lost.
The findings, published by The Nature Conservancy (TNC), adds that many other reefs are now "functionally extinct".
It blames poor fishing practices and coastal developments for the declines.
Lead author Mike Beck said the report showed that oyster reefs were the most severely impacted marine habitats on the planet.
"We're seeing an unprecedented and alarming decline in the condition of oyster reefs, a critically important habitat in the world's bays and estuaries," he said.
The study, written by scientists based in five continents, found reefs that were "functionally extinct" in a number of regions, including North America, Europe and Australia.
"However, realistic and cost effective solutions within conservation and coastal restoration programmes, along with policy and reef management programmes provide hope for the survival of shellfish," Dr Beck added.
Oysters provide a number of key services within their ecosystems, such as filtering water, and provide food for other organisms, such as fish, crabs and birds.
The assessment identified a number of "driving forces" behind the reefs' decline, including "destructive fishing practices, coastal overdevelopment, poorly managed agriculture and poor water quality".
Although these problems have been around for decades, the report said there were two main barriers that were impeding oyster recovery efforts.
The first was a lack of awareness that shellfish habitats were in trouble, and the second was an assumption that non-native shellfish can be introduced in areas where native species are declining.
"We want to raise awareness that the world's remnant oyster reefs and populations are important, since they represent some of the last examples of reef habitats produced by a particular species of oyster," explained co-author Dr Christine Crawford, from the University of Tasmania.
"We have an opportunity to conserve such reefs in Australia and elsewhere with the results of this assessment," she added.
Among the report's recommendations were to elevate native, wild oysters as a priority species for conservation, and ensuring existing protection policies were extended to include the vulnerable reefs.