Shockingly, more than half of North America’s freshwater mussels are in danger of going extinct. With the clock ticking, a small band of committed researchers is determined to save a group of molluscs that is critical to the health of our aquatic ecosystems
by Moira Farr
Spread across biologist Todd Morris’s palm is a cluster of mussels just scooped from the Grand River in Kitchener – to the untrained eye, a pile of clams. To the expert, a variety of thriving native invertebrate species with unique biologies as intriguing as their names: fatmucket, elktoe, creeper, fluted shell and – the one that has Morris most excited – the wavy-rayed lampmussel. “These guys are very cool,” says Morris, pointing to the distinctive “wavy rays” emanating from the mussel’s “beak” outward to the edge of its smooth, yellow green shell. The gravelly bottom of the shallow “riffle” (fast-flowing) section of the Grand River we are standing by is one of the few places in Ontario they are found. Since 1999, the wavy-rayed lampmussel has been listed as a species at risk by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and since 2004 designated endangered under the Species at Risk Act (SARA), as well as the Fisheries Act.
Morris is a research biologist with the Great Lakes Laboratory for Fisheries and Aquatic Sciences (Fisheries and Oceans Canada), based in Burlington, and a member of the Ontario Freshwater Mussel Recovery Team, formed in 2003 to gather information about, monitor and create a strategy for restoring the province’s threatened indigenous mussel species (see “The crisis”). The situation is critical: of the 41 native mussel species found in Ontario (all of them in the family Unionidae), 11 are endangered and one threatened. The declining populations of these species reflect North American trends: freshwater mussels are considered the most endangered species group on the continent; 65 percent of all North American freshwater mussel species are at risk of extinction.
Why should the average person care about freshwater mussels? The answer is simple, says Morris. “What threatens them, threatens us. When they disappear, it’s an early sign you’ll lose other species too.”
Freshwater mussels might also be called conservation underdogs. Because they lack the endearing faces of mammals or the beautiful colouring of birds or butterflies, their plight has not exactly captured the public’s imagination or the research dollars devoted to other species. That only makes malacologists (mollusc biologists) more determined to expand the knowledge base about freshwater mussels, spread the word about their precarious status and make a concerted effort to save the many species at risk.
Freshwater mussel beds provide stability and aerate the sediment at the bottom of lakes, rivers and streams, according to The Photo Field Guide to the Freshwater Mussels of Ontario, an excellent reference book by Burlington-based, National Water Research Institute biologist Janice Metcalfe-Smith (with Alistair MacKenzie, the late Ian Carmichael and Daryl McGoldrick). Individual mussels can filter up to 40 litres of water a day. They convert particles of organic material (including algae and bacteria), excreting phosphorus and nitrogen, which are important to other aquatic species such as plankton; they are a food source for fish, mammals and birds. Fish lay eggs in empty mussel shells, crayfish hide in them and insect larvae attach to them. They can live for decades, but are extremely sensitive to pollution and habitat changes. By accumulating toxins, they serve as early indicators of environmental degradation.
Native people harvested mussels, using them for food, jewellery and tools. Freshwater pearl hunting thrived in the 19th century. From the late 1800s until the 1940s, when plastics became commonplace, the Grand River supplied massive numbers of mussels to the button industry. Since the 1950s, freshwater mussel shells from the Mississippi River basin in the United States have been shipped in large quantities to Japan, where the shells are cut and placed inside oysters to produce cultured pearls.
But the chief culprit in recent regional declines of freshwater mussels is the notorious zebra mussel, native to European bodies of water and believed to have been dumped into the St. Lawrence Seaway in the ballast water of an ocean vessel from the Caspian Sea. Since 1988, when biologist Gerald Mackie (now retired from the University of Guelph) identified the first members of this invasive species found in North America, on the shores of Lake St. Clair, they have done more than clog water pipes and become a nuisance to boaters. Zebra mussels – unlike members of the Unionidae family, which require host fish to reproduce – broadcast their larvae into the water, robbing other species of the nutrients and oxygen they need to compete and survive. Zebra mussels also spread disease (suchas avian botulism) that has devastated the native fauna ofthe Great Lakes. As a result, struggling populations of native mussels remain in river areas only, primarily in southwestern Ontario, though also in eastern and north-eastern areas of the province.
Here in the southwest, native mussel species are threatened by changes in the ecosystem caused by agricultural runoff, damming and loss of habitat due to urban and suburban development, as well as declines in the host fish population that many need in order to reproduce. Unusual rain patterns due to climate change will affect water levels and the survival of wetland areas, where native species have found refuge. Fish species that serve as hosts to mussel larvae are affected by changes in water temperature and could decline in number, causing a subsequent crash in mussel populations. The decline of wetland habitats could force vulnerable species farther into water systems now overrun with zebra mussels, which will probably out-compete native mussels for resources.