“They are little treasures,” says Dr. Greg Cope, as he points out the freshwater mussels depicted in posters on his office wall. “But we are losing them. They are the most imperiled fauna in North America.”
In the 1800s, there were probably 50 to 60 species in North Carolina alone. Today, “depending on whom you believe and what day it is,” Cope says, 70 to 80 percent of those are listed as endangered, threatened, of special concern or already extinct.
Coming from a scientist who has spent 12 years studying mussels, Cope’s imprecision is telling. Scientists have a long way to go in their quest to better understand North Carolina’s freshwater mussels, why they are rapidly disappearing and what to do to stop the loss.
To fill in the knowledge gap, Cope and Dr. Damian Shea, both faculty members in the College of Agriculture and Life Sciences’ Department of Environmental and Molecular Toxicology, have teamed with scientists from several other N.C. State University colleges and state agencies to find out more about the mollusks — and especially about the role people have had in their decline.
In March, the researchers helped host a four-day international meeting that drew around 300 scientists to Durham to discuss advances in freshwater mollusk conservation. And now, along with their colleagues in the College of Veterinary Medicine, they are wrapping up a three-year study to assess the effect of road runoff on freshwater mussel populations in the Upper Neuse River Basin.
The study, funded by the N.C. Department of Transportation, is designed to give policymakers and bridge builders information they need to make better decisions — ones that encourage conservation and yet at the same time don’t impede local economic growth.
Because road and bridge construction has been implicated in declining mussel populations, federal laws designed to protect endangered species like the Carolina heelsplitter and the dwarf wedge mussel have stalled recent bypass projects in Johnston and Mecklenburg counties.
But no one knows precisely whether road construction contributes to the declines and, if so, how: Do the declines result from the habitat changes that construction brings about? Or from contaminants — the crankcase oil, combustion byproducts in automobile exhaust and herbicides used to control roadside weeds, for example — associated with transportation? Or is it the runoff generated by the subsequent development of homes and businesses that bridges open the way for?
And are some bridge construction types more likely to lead to problems?
To find out, Cope, Shea and other researchers selected 20 bridges in agricultural, forested and urban settings in Durham, Orange and Wake counties, then set about sampling Elliptio complanata populations upstream and downstream of the crossings. The mussels were weighed and measured, and their tissue and hemolymph — a fluid analogous to blood for some invertebrates — were studied to assess contaminant levels and overall health.
“ In general, we found lower populations of mussels and higher concentrations of contaminants below bridges,” Shea says.
While samples taken around forested and agricultural areas appear similar, findings were remarkably different in urban settings. Near bridges inside Raleigh’s beltline, “populations were lower to non-existent, contaminants were much higher and there were more physical changes to the habitat,” Shea says.
Now, the researchers are looking more precisely at their data to see if certain bridge construction materials or designs are associated with the health of mussels found nearby. They also plan to compare their findings with those from another study assessing the distribution of mussel populations around bridges and culverts. And, with support from another DOT grant, they will begin lab tests to determine how different levels of contaminants affect mussels.
“ This is giving us a better understanding of the influence of human activity associated with bridges,” Cope says. And that information should be essential in formulating construction and maintenance recommendations — or best management practices — that encourage conservation.
Recognizing that more multifaceted research, teaching and extension work must be done to arrive at sound recommendations, the N.C. State researchers have joined with biologists from the N.C. Museum of Natural Sciences, the N.C. Wildlife Resources Commission, the DOT and the U.S. Fish and Wildlife Service to form the North Carolina Mussel Conservation Partnership.ne of their goals is to raise the public’s awareness of the importance of mussels and their plight. With grant funds, Cope had 500 copies of museum curator Art Bogan’s “Workbook and Key to the Freshwater Bivalves of North Carolina” distributed to natural resource educators — including North Carolina Cooperative Extension agents and specialists — across the state.
Others in the partnership, including Dr. Jay Levine of N.C. State’s College of Veterinary Medicine, have created educational posters and activity books for school children.
The materials focus on some of the mussel’s more remarkable aspects: Many mussels live as long as — or longer than — humans, and their tightly closed shells allow them to survive up to a month out of water under certain conditions.
Otters, muskrats, raccoons and turtles eat mussels. And while humans tend to steer away from their tough, bland meat, people have found other ways to make use of the creatures. Until plastic buttons came along in the 1940s, there were thriving industries along the Mississippi and in the Midwest that turned the shells into buttons, Cope says. And pearls taken from marine oysters — they often start from “seeds” crafted from native freshwater mussel shells.
Beyond their utility, mussels also have a fascinating life cycle, spending part of their lives as parasites on the gills and fins of fish. Because mussels aren’t mobile, their mothers sometimes use trickery to get their larvae, or glochidia, onto passing fish. They stick out a mantle tissue resembling a minnow, and as the fish approaches or tries to swallow the lure, the mother releases a cloud of glochidia. The glochidia then attach to the fish, where they piggyback their way into adulthood.
This unique method of metamorphosis could be one reason that certain mussel species are so environmentally sensitive. Some types of mussels have evolved to survive on only one species of fish. So if that fish is overharvested, if it falls victim to some other environmental change or if it moves away to escape an environmental threat — as it might swim away from runoff from a bridge — then the mussel population that depends on it suffers.
While Cope and Shea are focusing on what happens in and around road crossings, they believe that their research is about much more than just bridges and bivalves. It’s about ensuring a good future — one that’s both economically and environmentally sound.
“ These organisms are extremely beneficial. They filter the water, remove contaminants and provide stability to the stream bottom. And so they help maintain water quality in streams, rivers and lakes. And when they are dying off, they are sending a signal that there’s a problem with water quality,” Cope says. “They are not this bad guy environmental obstacle they are made out to be.
“ People have to work together and find a way to balance ecological impact with transportation needs,” Cope says.
If decisions about development and conservation are to have the effect that’s
intended, then they need to be based on sound science,” Shea adds. “And
that’s what we want to provide.”