The Nature Conservancy. Protecting nature. Preserving life.™

By Megan Fetzer Sheehan

Which is the most imperiled marine habitat on Earth? Coral reefs? Mangrove forests?

You may be surprised at the answer: Shellfish reefs.

A new report authored by Nature Conservancy scientists and partners has found that shellfish reefs worldwide have declined dramatically—including the loss of 85 percent of oyster reefs globally.

“What we’re seeing is an unprecedented and alarming decline in the condition of oyster reefs, which are a critically important habitat in the world’s bays and estuaries,” says Mike Beck, senior marine scientist at The Nature Conservancy and a lead author of the report. 

And there's more at stake here than just fried clams. Shellfish are the ecosystem engineers of bays and estuaries and provide essential services to humans and nature, such as water filtration and coastline buffering.

Decimated Habitats

The “Shellfish Reefs at Risk” report provides the first global view of the condition of oyster reefs. Some of the report’s findings include:

• More than 85 percent of the world’s oyster reefs have been completely lost.
• In most bays around the world, shellfish reefs are at less than 10 percent of their original abundance.
• Only 10 ecoregions in the world presently report wild capture rates above 1,000 tons, down from millions of tons 50-100 years ago across some 40 ecoregions, and reefs in most of these ecoregions are in poor condition or functionally extinct.

The report’s findings clearly show that oyster abundance — and the health of shellfish reefs in general — has decreased exponentially over the last 100-150 years.

“Shellfish have been historically managed only for harvesting,” says Beck. “As a result, oyster reefs habitats are now highly threatened around the world."

The Culprit for Shellfish Loss

Why has this happened? Shellfish are at risk today mostly because of destructive fishing practices — including the overharvesting of shellfish — and loss or degradation of their coastal habitat. 

Specific threats to shellfish reefs include:

• Destructive fishing practices (such as dredging) that damage reef habitat;
• The overharvesting of shellfish, even in reefs that only support 10 percent or less of the original abundance of shellfish;
• The introduction of non-native shellfish to bays and estuaries, and with them new parasites and diseases;
• Habitat loss from coastal development and dredging of shipping channels; and
• Declines in water quality.

Despite these threats and the current state of shellfish reefs, the report concludes that every continent has key opportunities for shellfish conservation and reef restoration.

But conservationists must overcome a glaring obstacle before progress can be made and the fate of shellfish altered.

Sustaining Shellfish Populations

The biggest challenge for shellfish conservation is that people have traditionally viewed oysters merely as fisheries and haven’t considered the effects of overharvesting on the reef ecosystems.

There is also a common misconception that non-native oysters can replace the native ones lost over the years. However, non-native oysters rarely provide reef habitat and their introductions have caused a whole host of new problems from invasive species and diseases in our bays and estuaries.

Shellfish aren’t completely doomed, however. The report provides recommendations for bringing shellfish reefs back from the brink, including:

• Improving protection for native shellfish reefs and creating spawner sanctuaries;
• Restoring and revitalizing reefs by using existing funds better;
• Managing fisheries sustainably for ecosystems and livelihoods;
• Stopping the intentional introduction and spread of non-native shellfish; and
• Improving water quality in bays and estuaries.

Through the Shellfish Restoration Network and a partnership with NOAA, the Conservancy is working to protect and restore shellfish populations around the United States from oysters in the Indian River Lagoon in Florida to clams in the Great South Bay of New York.

“All hope is not lost, though, if we take action now,” adds Beck. “Ensuring that oyster reefs and other shellfish habitats are managed as critical components of coastal ecosystems and garnering commitments from policymakers and managers for conservation and restoration will ensure that shellfish reefs are around for future generations."