Volunteers plant oysters on a reef in the Severn River. CBF's restoration vessel Patricia Campbell sits nearby. Photo by CBF Staff.

Oysters are Thriving on CBF Reefs

Let's give a warm, watery welcome to billions of new Maryland residents: oysters. That's how many baby bivalves or "spat-on-shell" have been planted on man-made Maryland oyster reefs in the past few years by the Oyster Recovery Partnership (ORP).

So far this summer,  CBF, one partner in ORP, has put down about four million additional spat on four reefs in the Severn, five million on the Choptank, and two million at the confluence of the West and Rhodes Rivers. By the end of the summer CBF will also have deployed an additional 1,200 reef balls at the Cook’s Point Oyster Sanctuary, each serving as artificial habitat on which oysters can grow.

It's difficult to determine exactly how many of the billions of oysters planted over the past 12 years have survived. Scientists are researching the question. It's tough growing up an oyster in the Chesapeake, where disease, low oxygen levels from pollution, and other factors make life difficult.

A 2011 state survey of oyster bars in the Bay revealed a 92 percent oyster survival rate, the highest since 1985. The Washington Post called the news “a modern-day Lazarus story.” A team of divers from the Paynter Labs at the University of Maryland checked several reefs in the Severn River in the fall of 2011 and found encouraging results. CBF first built those reefs in 2005, and has added oysters over the years. A Paynter Lab report to CBF had this to say:

"More oysters were observed that (sic) originally expected and most oysters were very large. The oyster densities at these sites have remained high over the past seven years and disease intensity has remained very low. Considering the low densities of oysters often observed on restored bars in Maryland, the perpetuation of relatively high densities of large, healthy oysters at this site is an example of successful oyster restoration in Maryland."

Those findings in November were especially welcome because record spring river-flows together with Tropical Storm Lee dumped so much fresh water in the Chesapeake Bay that salinity levels plunged, and many oysters in the upper Bay died as a result. The Severn oysters apparently weathered those storms, as did oysters in the large majority of restored reefs south of the Chesapeake Bay Bridge. 

Keystone species

Oysters are what scientists call a "keystone species" in the Bay, meaning their survival is critical to the estuary's ecology. A single adult oyster can filter up to 50 gallons of water a day. Millions of them concentrated in a river such as the Severn can act as filtering factories. And with all the pollution pouring into the Severn from sewage spills, urban and suburban runoff, septics, and other sources, we need all the help we can get.

Oyster reefs also provide ideal habitat for tiny aquatic life and the fish that feed on them. A healthy oyster reef is one of the most diverse "communities" in the Chesapeake ecosystem.  This concentration of life makes them favored fishing sites for watermen and anglers.

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