Craig Krajeski
Native Freshwater Unionids
Ecological Benefits and Threats

What is a unionid?
 Bivalve mollusks that live in freshwater, also known as freshwater mussels (Freshwater
Mussels 2010)
 Filter feeders - constantly pump water to feed and breathe, gills capture oxygen and food
 Live in soft but stable sediments (mainly sand and small gravel) in lotic and lentic
systems such as streams, rivers, ponds, and lakes
 To move, unionids extend their foot out of the shell and into the substrate.
 Reproduction
 Inside the female unionid, fertilized eggs develop into microscopic larvae called
glochidia
 Unionids need to infect a host fish with larvae to complete the reproductive process
 Once the glochidia are released from the female, they must attach to the gills or the
fins of the right fish host and encyst to complete development (Grabarkiewicz 2008)

Ecological benefits and importance of unionids?
 Food for fish, raccoons, river otters, mink muskrats and many others
 Unionid beds create habitat for many other invertebrates
 As filter feeders, they may clean harmful bacteria and parasites from the water
 Stabilize the lake or stream bottom and shells provide an important substrate for algae
and insect larvae to attach (Freshwater Mussels 2010)

Threats to unionid populations and diversity
 Dams - block the movement of fish hosts and turn free flowing streams into a series of
lakes or pools, and make the survival of mussels that are adapted to a lotic environment
difficult or impossible (Wege 2010)
 Exotic species – zebra mussels affect native unionids by attaching in large numbers to
any exposed area of the native mussel's shell, eventually causing death due to suffocation
(Wege 2010)
 But unionids are adept at avoiding zebra mussels
 Sedimentation - combination of intensive land use, wetland drainage, and stream
channelization results in high rates of soil loss. This buries mussels and suffocates them.
 Pollution - unionids are extremely sensitive to certain pollutants such as ammonia and
heavy metals (Virginia Cooperative Extension 2010)

Recent publication
 “Assessing Causes of Change in the Freshwater Mussels (Bivalvia: Unionidae) in the
Black River, Ohio” by Lyons, et al in The American Midland Naturalist (2007).
 Investigated the diversity and abundance of unionid mussels in Black River watershed
and compared results to urbanization locations, to site-specific appearance of the habitat
and to a 1997 fish survey.
 Concluded that unionid assemblages in the Black River appear typical for the region with
relatively abundant, but low diversity communities upstream of the cities that line Lake
Erie's coast and diverse, but small and potentially threatened, populations in the urban
regions.
Craig Krajeski

Conclusion - Unionids are an integral component of aquatic ecosystems and their wealth of
diversity in North America is unmatched anywhere else in the world. They are key
bioindicators and are in desperate need of conservation.
References
Freshwater Mussels. Freshwater Mollusk Conservation Society. Retrieved November 7, 2010
from http://molluskconservation.org/MC_Ftpage.html.
Grabarkiewicz, J.D., Davis, W.S. 2008. An Introduction to Freshwater Mussels as Biological
Indicators. United States Environmental Protection Agency. Retrieved November 7,
2010 from http://www.epa.gov/bioiweb1/pdf/EPA-260-R-08015AnIntroductiontoFreshwaterMusselsasBioindicators.pdf.
Hoggarth, M.A., Rice, D.L., Grove, T.L. 2000. The correlation of mussels with fish in the upper
Blanchard River in Hardin and Hancock counties, Ohio, with special regard to the rayed
bean (Villosafabalis). Ohio Biological Survey, 19-26.
Lyons, M.S., Krebs, R.A., Holt, J.P., Rundo, L.J., Zawiski, W. 2007. Assessing Causes of
Change in the Freshwater Mussels (Bivalvia: Unionidae) in the Black River, Ohio. The
American Midland Naturalist, 158. 1-15.
Virginia Cooperative Extension. Sustaining America's Aquatic Biodiversity - Freshwater Mussel
Biodiversity and Conservation. Virginia Tech. Retrieved November 7, 2010 from
http://pubs.ext.vt.edu/420/420-523/420-523.html.
Wege, G. Freshwater Mussels of the Upper Mississippi River System. U.S. Fish & Wildlife
Service. Retrieved November 7, 2010 from
http://www.fws.gov/midwest/mussel/index.html.