Bivalve Blues

Report Reveals Global Risks for Oyster Reefs

Exposed oyster reef in the Chesapeake Bay, Virginia (NOAA)

Baymen harvest an average of roughly 99,000 tons of oysters each year from the warm waters of the Gulf of Mexico. But that kind of bounty is now uncommon: Around the world, 85 percent of shellfish reefs have been lost to overfishing and habitat destruction, according to a new Nature Conservancy report, Shellfish Reefs at Risk.

“Shellfish reefs are the single most impacted marine habitat globally,” says Mike Beck, a Conservancy marine scientist and lead author of the report. Beck and his team of scientists compiled status reports from more than 144 estuaries and found that reefs were in significant decline worldwide.

While records show that even the ancient Romans exploited shellfish reefs, the pressure on oysters, mussels and clams today is unprecedented. Overharvesting has led to the functional extinction of many oyster reefs throughout Europe, North America and other continents. In fact, most of the oysters we eat now come from aquaculture.

Global condition of oyster reefs (via The Nature Conservancy report)

Other major threats include disease and parasite outbreaks; the introduction of non-native species; pollution from the filling and dredging of coastal areas; and runoff from urban development, industry and agriculture.

Most countries tend to manage oyster reefs as harvesting fields and not much more, Beck says. We underappreciate and undervalue the “ecosystem services” that shellfish reefs provide, he says, such as filtering and purifying water, controlling erosion and supporting scores of other marine species.

While providing a global assessment of the threats facing shellfish, the report also outlines steps to help protect and restore threatened reefs. The scientists recommend that governments protect some of the best remaining reefs in places like the Gulf of Mexico and Georges Bay in Australia.

Beck also calls for new and existing funding to focus on the long-term restoring of reefs, not just on oyster harvesting; many restoration projects now allow harvesting only a year or two after oysters have been replanted. “We should allow reefs to rebuild themselves. And then we should allow harvesting of just the interest, not the principal,” says Beck. “We need to see the reefs return, not just the oysters.”

-Joshua Zaffos