By Erica Goldman

A powerful filter feeder, the marsh mussel Geukensia demissa grows attached to the root-like rhizomes of the cordgrass Spartina. In the Delaware Bay, these mussels filter more than six times what current populations of oysters can. Photograph by Danielle Kreeger.

Until we bring back oyster reefs, the mainstem of the Bay may remain poorly served by filter feeders. But what about upstream? Could restoring freshwater filter feeders in streams help clear the water before it ever reaches the larger rivers or the mainstem Bay?

Researchers are already addressing similar questions in the nearby Ohio and Delaware watersheds. Could these efforts prove useful models for the Chesapeake?

On the Ohio-West Virginia border, natural resource managers recently embarked on a mission to restore degraded biological resources in one stretch of the Ohio River. Their approach: re-establish the filter power of a complex assemblage of freshwater mussels to improve water quality enough to enable other species to come back. If they succeed, this restoration effort will prove a hallmark event, says Catherine Gatenby, a biologist with the U.S. Fish and Wildlife Service in White Sulphur Springs, West Virginia. This project will test the theory that managers can use organisms like filter-feeding mussels to jumpstart the restoration of a complete biological community.

Unfortunately, it took an ecological disaster to ignite this innovative call to arms. In June 1999, a metal manufacturing facility in Marietta, Ohio allegedly released hazardous materials into the Ohio River. The spill reportedly killed an estimated 8,600 fish, 990,000 mussels, and 12 million snails along one stretch of the river.

The United States and the states of Ohio and West Virginia filed suit in the U.S. District Court for injuries to natural resources under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and for violations of the Clean Water Act. The suit settled out of court in early 2006 and the companies paid $2.04 million specifically targeted towards rebuilding freshwater mussels, fish, and snails. This provided a dedicated source of funds for a restoration effort.

The 1999 spill wiped out at least 20 different species of mussels, explains Gatenby, some endangered species, some not. As a group, freshwater mussels are the most imperiled fauna in North America, with 43 percent of the 300 species of freshwater mussels currently in danger of extinction. The U.S. Fish and Wildlife Service (USFWS) holds an obligation to restore endangered species of mussels under the terms of the settlement, she adds.

What makes this restoration plan unique, she says, is that restoration will include the whole community of mussels in the assemblage — endangered and not. "Before we can restore the endangered species, we have to restore the habitat," says Gatenby. In this case that habitat includes the entire bed of mussels. This argument enabled biologists to convince the trustees in the lawsuit to include not only endangered but common species of mussels in an integrated restoration plan, a decision that Gatenby thinks will maximize ecological gain for economic investment.

How much filter power are scientists and managers trying to bring back to the Ohio River? Since one mussel can filter approximately six gallons of water per day and roughly 990,000 mussels were killed, the arithmetic of scale implies that this 10-mile stretch of river lost six million gallons per day of filtering capacity. That is a lot to bring back, but the members of the Mussel Habitat Partnership are optimistic. Not only do they think that they can restore the mussel bed but that the mussel bed itself will in turn modify the environment in a way that promotes the recovery of fish species and other invertebrates lost in the ecological calamity.

Gatenby's team from White Sulphur Springs National Fish Hatchery, the Ohio River Islands National Wildlife Refuge, and the West Virginia Division of Natural Resources transplanted the first 800 common mussels to the river in mid-May, kicking off what will be a ten-year restoration effort. Once the mussels get acclimated and begin to filter in earnest, the site will be reassessed to determine whether the habitat proves suitable for reintroduction of some of the endangered species.

Meanwhile in Brandywine River in Pennsylvania, a tributary that empties into Delaware Bay, Danielle Kreeger is taking a similar approach to restoring freshwater mussels for their water quality services up in the non-tidal portions of the watershed. Based at the Partnership for the Delaware Estuary and also Drexel University, Kreeger focuses on Unionids, the same group of freshwater mussels at the focus of the USFWS project in the Ohio River.

These mussels were once quite common in the Delaware watershed but their population dropped from historic levels nearly 200 years ago. Scientists believe that the population decline resulted from habitat loss, dams that interfered with the transport of larvae, and degraded water quality. Today only one species of Unionid — Elliptio complanata — remains out of at least 7 or 8 originally. These mussels can live up to 80 to 100 years. Right now, only old mussels are thriving in the Brandywine and Kreeger has not found any younger than 30. She suspects that the system of 11 dams in the lower part of this watershed is to blame. Recruitment of larval mussels depends on fish that serve as intermediate hosts. The fish cannot pass through these dams, which interrupts the life history of the mussel — a problem likely also to be true for freshwater mussels in the Susquehanna basin of the Chesapeake watershed as well.

Building on the Partnership for the Delaware Estuary's attempts to restore oysters and other native shellfish species in the tidal portion of the estuary, Kreeger has just launched a project to restore some of the species lost from the Brandywine and several adjacent streams in southeast Pennsylvania, hypothesizing that they would fill vacant ecological niches. Some environmental managers in the state of Pennsylvania have expressed interest in the potential of this approach for decreasing pollution, reducing total maximum daily loads (TMDL), she says. According to Kreeger, managers view this approach as another key tool for their restoration toolkit — one with the potential to improve the Delaware Bay itself by decreasing the load of nutrients flowing from the watershed.

Down in the tidal portion of the estuary, she's mainly working to boost populations of the ribbed mussel Geukensia demissa, which lives in salt marshes. There it attaches to the root-like rhizomes of the marsh grass Spartina. Beds of these mussels could play an important role in stabilizing shorelines subject to erosion from sea level rise, as well as performing the usual bivalve services such as improve water clarity. The marshes are the "the lungs and kidneys for the bay," Kreeger says. "Everything depends on these marshes but we are losing them to erosion." Kreeger aims to put mussel and oyster communities back in the subtidal and intertidal regions to harden the shoreline with living reefs.

If you're interested in building shellfish reefs and beds for ecosystem services, rather than historical or commercial purposes, species like the marsh mussel are preferable to oysters, she asserts. "They're great. You can spawn them, seed beds with them. You can do all of these great things for water and habitat quality," she says. And the biggest sell, she notes — no one eats them and they're not susceptible to disease.

"We are talking about restoration in the Delaware from the mouth of the bay to the headwaters up in New York," she says. It's worth asking the same questions for the Chesapeake, says Kreeger.

This page was last modified September 15, 2018