Some years back, conservation paleontologist Rowan Lockwood of William & Mary college in Williamsburg, Virginia, went to one of the few surviving fossil reefs, near Dutton, Virginia. She had long wanted to find out what the oyster reefs of the Chesapeake Bay used to be like before people started large-scale harvesting there.
When this reef was formed 245,000 to 195,000 years ago, the sea level was higher, so that today, the fossil reef sits well out of the water in the cliff face along the Piankatank River. “The oysters are all in life positions, still articulated,” says Lockwood. “They look like they died yesterday.” To interpret the fossils, she teamed up with marine biologist Roger Mann, also from William & Mary, who has been closely monitoring the Chesapeake oyster population for decades.
Based on the Dutton-area fossil reef as well as an extensive collection of shells in the Virginia Museum of Natural History taken from fossil reefs that no longer exist, Lockwood and Mann estimated that long ago, local oysters used to live four times as long (up to 21 years) and grow twice as big (up to 25 centimeters in diameter) at nearly 10 times the density of reefs in the area today.
This means that filter-feeding oysters would have been able to pass all of Chesapeake Bay’s water through their gills in one day, Mann and Lockwood calculated. Today, that might take close to a year.
If these giant reefs would magically reappear today, it might solve many of the bay’s problems. Nutrient-rich agricultural runoff and sewage cause huge algal blooms, and when these algae die and sink, bacteria bloom in turn, consuming so much oxygen that few other organisms survive at lower depths. “Lots of oysters could turn much of this stuff into oyster tissue and shell instead,” says Lockwood.
But how much recovery is realistic? “It would be naive to think we can restore these systems to what they were like before we put 18 million people in the watershed of the Chesapeake Bay. That’s simply not going to happen,” Mann says. “What existed even a few hundred years ago will never, ever be recreated.”
And neither Mann nor Lockwood sees much value in the current, large-scale practice of releasing live larvae or young oysters into the bay. They say it is costly and that the large majority of released larvae are probably swiftly consumed by predators. “It’s like flushing them down the toilet,” says Lockwood.
But, inspired by the astonishing size of many of the fossil shells, Lockwood argues that recovery could be significant if the practice of dredging was halted and restoration efforts were aimed at protecting large adult oysters, which filter more water, produce more offspring and help reefs grow tall.
This would require the introduction of large, solid structures that mimic the reefs that have been destroyed, she says. These would keep oysters from getting covered by the large amounts of sediment that wash into the Bay. They would also prevent dredging, which would be good for oysters — but not for fishers. “Watermen have been here for hundreds of years, and it’s a generational livelihood that we need to preserve,” she says. “So you’d have to be careful where you put these structures.”
How about we just stop harvesting wild oysters for 5-10 years and see if they can expand?
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