Oysters are disappearing from coastlines around the world because of overharvesting and disease, researchers said.
An estimated 85 percent of global wild oyster reefs and beds vanished in the past 20 to 130 years, according to a study led by Michael Beck, lead marine scientist at the University of California at Santa Cruz. His team examined oyster reefs in 144 bays across the world, historical records and national catch statistics in a study published in the February issue of the journal BioScience. The condition of oysters was rated as “poor” overall.
“Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide,” the authors said. “Overharvest and disease often lead to a population crash.”
Oysters were rated “functionally extinct” in previously abundant coastal areas including Rhode Island’s Narragansett Bay and Northern Europe’s Wadden Sea, which have less than 1 percent of former reefs remaining.
While oyster disease occurs in native populations, in “many places” the occurrence of illnesses is linked to the transfer of non-native oysters from aquaculture and ships’ ballast water, according to the researchers.
In 70 percent of bays, the mollusks are at less than 10 percent of their prior abundance, the researchers said. The study may underestimate losses because of a lack of historical abundance records, particularly for South America, Asia and South Africa, they said.
“Given the severity of oyster reef loss, the need for action is clearly urgent,” the researchers said. “This loss is not just a problem of the past. Oysters are still managed without regard for the structure or function of reefs.”
Unmanaged harvesting is still taking place in countries including Ireland, Australia and the U.S. and wiped out oyster populations as recently as the 1990s in Greece and Colombia, according to the study. The researchers advised taking measures including reef conservation, fisheries management and controlling the spread of non-native shellfish.
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