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Oyster populations worldwide have plummeted and in some areas may be considered extinct, according to a study released this month by scientists at UC Santa Cruz and the Nature Conservancy.
The study examined 144 bays across 44 different ecosystems and estimated that 85 percent of oyster reef habitat worldwide has been lost. Many bays – including Elkhorn Slough, Morro and San Francisco – have lost 99 percent or more of their oyster reefs.
To assess the current health of oyster reefs, the researchers used historical documents and recent fishing records to provide baseline comparisons. They then rated each bay and region as "good" (if less than half the oyster reefs were lost), "fair" (50 to 89 percent gone), "poor" (90 to 99 percent gone), or "functionally extinct" (more than 99 percent gone). Oysters from all four bays examined in California (including the Southern California Bight) were considered functionally extinct.
Oyster reefs and beds are critical components of marine ecosystems, producing reef habitat for a variety of organisms. They provide a way to estimate a marine ecosystem’s health because most of the underlying reef structure is created by just one or two oyster species.
Oysters filter water and clarify it, promoting the growth and survival of a variety of organisms, including seagrass. They also reduce harmful algal blooms and protect shorelines from erosion and storm surges, and provide a platform for other marine life.
The study, published in the February issue of BioScience, reported that oysters populations can be recovered “through conservation, restoration and management of fisheries and nonnative species.”
For many other fisheries, rebuilding plans are being developed, and there have been some important successes,” said Michael W. Beck, senior scientist at the Nature Conservancy and lead investigator for the study. “However, plans for rebuilding oyster populations are rare.”
Beck and his colleagues recommend that fisheries stop in areas where less than 10 percent of the original oyster population remains. They also say fisheries need to halt harmful practices, such as dredging.