Black sandshells (Ligumia recta) were
once common in the Cedar River. Natural resource managers
hope to determine and eliminate the cause for low mussel abundance
in the Cedar River so that mussels, like the black sandshell,
can be reintroduced back into the former mussel bed locations.
The many fine threads in the photo are byssal threads put
out by these young mussels to secure themselves to the substrate
so that they do not get washed away during floods.
Photograph by USFWS; Robert Pos
The Cedar River is a large river ecosystem in east central Iowa
with rich cultural and natural histories that are threatened by development and human
use. Efforts to restore natural resources and balanced uses will
contribute to a clean and safe environment, provide outdoor recreation,
and preserve Iowa and American heritage.
The Cedar River historically supported healthy and diverse numbers
of freshwater mussels. In fact, the Cedar River was chosen as
a location to reintroduce the State and federally listed endangered Higgins eye pearlymussel as part of a recovery
project for the species. However, during follow up monitoring
of the reintroduction work, no Higgins eye mussels could be found.
Surveys for other mussels also found that numbers seem to be down
as indicated by the difficulty in finding live specimens. The
Iowa Department of Natural Resources and the U.S. Fish and Wildlife
Service are concerned because of the importance of mussels in river
ecosystems and because the decline in mussels indicates that the
river likely has problems that have not been identified. The mussel
declines could be due to water quality problems. Therefore,
the Service’s Rock Island, IL Ecological Servcies Field Office
has teamed with the Iowa Department of Natural Resources to conduct biomonitoring studies to determine
whether problems with water quality have caused the mussel declines
in the Cedar River, and if so, the exact nature of the water quality
problems. The results of the biomonitoring can be used by biologists
to re-start stocking mussels back in areas of suitable habitat without
water quality problems.
Immature freshwater mussels were placed in
small concrete domes that sit on the river substrate referred
to as mussel silos. The mussel silo contains a hollow center
which allows a chamber holding juvenile mussels to be placed
inside. Water flow over the silo creates a difference in
current which pulls water through the chamber providing the
mussels inside with oxygen and food. The sentinel mussels
can be moved to various locations to monitor their health
and growth and help narrow in on any water quality problems.
Mussels provide ecological services that benefit the public.
They filter water and contribute to the biological diversity in
river ecosystems. High biological diversity provides resilience
that helps system rebound from natural and man-made impacts to rivers.
Mussels help stabilize river substrates and mussels beds actually
act as a substrate, colonized by a variety of other aquatic invertebrate
species. These invertebrate species are in turn attractive to
bait fish and game fish that feed on the bait fish. Mussels are
declining at an alarming rate with up to 1.2% of the North American
species becoming extinct every decade(Ricciardi A. and J.B. Rasmussen. 1999. Conservation Biology, 13(5):1220-1222).
Map of the Cedar River and Iowa River drainages.
Iowa River is on the left and the Cedar River is on the right.
The Cedar River runs from southern Minnesota to its’ confluence
with the Iowa River in southeast Iowa flowing through the towns
of Austin, MN, Cedar Falls, IA, Waterloo, IA and Cedar Rapids, IA.
Cedar Rapids experienced serious flood events from the Cedar River
in 1993 and 2008. The non-government conservation organization,
American Rivers, is concerned about the structural proposals that
may be offered to address flooding along the Cedar River and this
is the reason that the Cedar River was named by American Rivers
of America’s most endangered.” About 31% of the Cedar
River in Iowa is listed
as impaired due to bacteria contamination, nitrate exposure,
and declining mussel populations.
Mussel Environmental History in the Cedar River
Mussel diversity and abundance are monitored
during periodic surveys of Iowa's rivers.
Photo by Mike Coffey; USFWS
In 2000, the Iowa State University surveyed mussels in the Cedar
River and compared the results to a similar study conducted in 1985.
The results indicated a decline in excess of 50% for the Cedar River
mussel population. As part of a follow up monitoring
in 2005 after the release of Higgins eye into the Cedar River
no Higgins eye pearly mussels were found. In addition, the monitoring
also indicated that only 43 live mussels of 9 species were found.
Future restocking of Higgins eye pearlymussel was stopped because
of the decline in the mussel community. The Iowa Department of
Natural Resources surveys mussels in many of their large rivers
including the Cedar River. Recently, it took State fishery biologists
almost 38 minutes to find a live mussel at known mussel bed locations
in the Cedar River compared to nearby rivers where it took between
3.2 to 5.9 minutes.
Data from the 2011 Summer
Links to More Information
gage in Cedar Rapids, Iowa
Iowa Department of Natural Resources
Mussels of Iowa
Genoa, Wisconsin National
U.S. Army Corps of Engineers - Higgins eye Mussel Relocation Plan
Rock Island Field Office Home