Shellfish reef. (Photo: Environment South Australia)

Australia´s shellfish reefs show worrying decline

A new research confirms that around  90-99 percent of Australia’s shellfish reefs have disappeared, making them the most threatened ocean ecosystem.

Reefs formed by the Australian flat oyster are the ones with the most dramatic decline. The study also shows that out of 118 historical locations containing ecosystems developed by the Flat Oyster, only Georges Bay, Tasmania, remains.

The native rock oyster is the second species with the most severe decline, of the 14 species covered in the study, with only six locations known to still contain their ecosystems out of 60 historical locations.

The research was led by Nature Conservancy, and involved 15 scientists from 10 organisations across Australia, and the results were published in the scientific journal Plos One.

“We already knew shellfish reefs were in bad shape globally with 85 percent of them lost or severely degraded,” said study leader Dr Chris Gillies, Marine Manager at The Nature Conservancy Australia.

“Our study confirms the situation for these important marine habitats in Australia is even worse with less than 1 percent of Flat Oyster and 10 percent of Rock Oyster habitats remaining,” he added.

The research highlights that the main reasons for the reefs’ decline are overfishing for food and lime production from the shells, destructive fishing practices (for instance, dredging), habitat modification, disease outbreaks, invasive species and a decline in water quality.

Dr Ian McLeod, co-author of the study from James Cook University, reported: “For many Australians today, the Great Barrier Reef probably first springs to mind as our most endangered ocean ecosystem," Dr Ian McLeod, co-author of the study from James Cook University, reported.  "While it and other coral reefs are indeed under threat, it’s the shellfish reefs that have really suffered the most. It’s just that most of them disappeared before we were born so people aren’t aware we’ve lost them.”

Researchers explain that oysters and mussels are ecosystem engineers that create, modify and maintain important habitat for a range of other species at a system-wide scale.

The study highlights that the loss of these habitats negatively affects the economic and social wellbeing of coastal human populations, reducing the productivity of fisheries, increasing pollution risks to coastal communities and industries (e.g. aquaculture) and by increasing the cost of protecting coastal assets with built infrastructure like seawalls.

The degradation of coastal ecosystems also contributes to the release of stored carbon, worsening climate change and increasing coastal risks associated with more frequent and intense storms, sea level rise and ocean acidification.

The study makes three major recommendations:

• Educate the community on the function and value of shellfish ecosystems.
• Protect all remaining shellfish ecosystems and eliminate current and future threats by protection under Commonwealth and State Government threatened ecological community, flora and fauna, and fisheries policies and legislation.
• Invest more in shellfish reef restoration projects.

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