Australia's shellfish reefs are the country's most threatened ocean ecosystem and are almost extinct, according to a new study.
Led by The Nature Conservancy, the study found that more than 90 per cent of shellfish reefs have disappeared off the nation's coastlines and those remaining are more endangered than the Great Barrier Reef.
Study leader Dr Chris Gillies says globally, 85 per cent of shellfish reefs, made up of species such as mussels, have been lost or severely damaged, but in Australia it is "even worse".
"Our study confirms (Australia has) less than one per cent of Flat Oyster and 10 per cent of Rock Oyster habitats remaining," Dr Gillies said.
Dr Ian McLeod, senior research scientist at James Cook University, says some of the main reasons for the reefs' decline are overfishing, disease, invasive species and a decline in water quality.
Scientists say oysters and mussels can form important habitats for a range of species and can help create reefs and beds which provide a range of ecosystem services.
The loss of these habitats could affect the economic and social wellbeing of coastal populations, contribute to worsening climate change, and increasing the risks associated with intense storms and rising sea levels, the study has found.
But Dr Gillies says Australia is well equipped to reverse the decline of shellfish ecosystems, with a number of existing projects under way with the assistance of private and government funding.
"There is still time to arrest the decline in shellfish reefs," he said.