By Timothy Wheeler

Can restoring oysters in the Chesapeake Bay and its rivers really help clean up polluted waters?

For many engaged in the struggle to save North America’s largest estuary, it’s an article of faith to answer that question with a resounding yes. Maryland, Virginia and the federal government have invested $76 million so far in trying to rebuild and repopulate oyster reefs in just six of the Bay’s tributaries.

With oyster populations worldwide much diminished, real-world evidence has been lacking to support the belief that restoring shellfish abundance will greatly benefit water quality — until now.

A research team led by the University of Maryland Center for Environmental Science has found a place along Florida’s Atlantic coast, near St. Augustine, where oysters grow so thickly that they resemble what Capt. John Smith and other European settlers reported finding in the Chesapeake Bay in the early 1600s.

Close analysis of the number and density of oysters in Florida’s Guana, Tolomato and Matanzas rivers and the locations of their reefs indicates that the bivalve population there filters 60% of the water in that small, somewhat protected system in a little less than two weeks’ time, researchers concluded.

“If you were to restore oysters to historic levels, this is the affect they would have,” said Matthew Gray, an oyster researcher at UMCES’ Horn Point Laboratory. He is lead author of the study, published in November in the journal Estuaries and Coasts.

It’s been more than three decades since Roger Newell, another oyster biologist at Horn Point, now retired, stirred imaginations by estimating that the Bay’s oysters had been so plentiful before 1880 that they could filter all of the estuary’s water in less than a week. His study and other similar ones helped inspire efforts to restore the Chesapeake region’s bivalve population, now thought to be just one or 2% of historic levels.

For Gray, the Florida study provides some contemporary evidence of the role oysters can play in water quality.

Gray had been quoted in a 2020 Bay Journal story puncturing the oft-repeated claim that an oyster can filter up to 50 gallons of water per day. While maybe true under ideal conditions in a lab, he said, studies indicate individual oysters in the wild siphon water through their gills at a far lower rate: 3 to 12.5 gallons per day.

That news story, which Gray likened to “popping somebody’s bubble,” bothered some Bay advocates, who feared it would undermine public support for oyster restoration.

About the Author: Tim Wheeler is the Bay Journal’s associate editor and senior writer, based in Maryland. You can reach him at 410-409-3469 or twheeler@bayjournal.com.

Photo Information: Matthew Gray, a scientist at the University of Maryland Center for Environmental Science, sits on a huge pile of oyster shells at the center’s Horn Point Laboratory. Photo by Dave Harp.