Oysters Vanishing From Oceans Worldwide, Biologists Say

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Oysters are "functionally extinct" in many locations around the globe due to disease and overharvesting, a new study has found.

The wide-ranging survey, published in BioScience, the journal of the American Institute of Biological Sciences, compares the past and present condition of oyster reefs around the globe. The international team of researchers led by Michael Beck of the Nature Conservancy and the University of California found that more than 90 percent of former reefs have been lost in most of the "bays" and ecoregions where the prized mollusks were formerly abundant.

In many places, such as the Wadden Sea in Europe and Narragansett Bay, oysters are rated "functionally extinct," with fewer than 1 percent of former reefs persisting. The declines are in most cases a result of over-harvesting of wild populations and disease, often exacerbated by the introduction of non-native species.

"Overall, we estimate that 85% of oyster reefs have been lost globally," the study says. "Most of the world’s remaining wild capture of native oysters comes from just five ecoregions in North America, yet the condition of reefs in these ecoregions is poor at best, except in the Gulf of Mexico."

Beck's team examined oyster reefs across 144 bays and 44 ecoregions. It also studied historical records as well as national catch statistics. The BioScience authors rate the condition of oysters as "poor" overall.

Oysters provide important ecosystem services, such as water filtration, as well as food for people. The survey team argues for improved mapping efforts and the removal of incentives to over-exploitation. It also recommends that harvesting and further reef destruction should not be allowed wherever oysters are at less than 10 percent of their former abundance, unless it can be shown that these activities do not substantially affect reef recovery.