FreshwaterMussels
America’s Hidden
Treasure
®
®
U.S. Department of the Interior
U.S. Fish & Wildlife Service
http://www.fws.gov
National Wildlife Federation
http://www.nwf.org
For the Record
No other country in the world equals
the United States in freshwater mussel
variety. While all of Europe supports only
12 species, nearly 300 kinds live here,
mostly within the vast watershed of the
Mississippi River.
Unfortunately, these animals may be the
most troubled natural resources in this
country. It’s estimated that 70% (Williams,
et al, 1993) of our freshwater mussels are
extinct, endangered, or in need of special
protection. Many of their problems stem
from how they live and changes that
have occurred to their habitat during
the past 200 years.
Life Down Under
Most freshwater mussels live burrowed
in sand and gravel at the bottom of rivers
and streams. Only a few are adapted to the
quiet water and muddy depths of lakes,
ponds, and reservoirs.
Unlike most animals, which must travel
in search of food, their food drifts to them,
mainly tiny plants and animals called
plankton suspended in the water. By
drawing water inside their shells through
a siphon, their gills filter out food and
take in oxygen.
Mussels usually don’t move much, but a
muscular “foot” helps them burrow and
allows limited travel if
disturbed by floods
or drought.
The foot also helps anchor them against
strong currents and may prevent a hungry
muskrat from tugging them out for its
dinner! A mussel’s shell, however, provides
its main protection from predators.
Their hard, calcium-based shells consist
of two halves joined by a hinge. Unique
names like “monkeyface,” “threehorn
wartyback,” and “pink heelsplitter” refer
to the wide range of shell size, color, shape,
and texture found among mussel shells.
Something “Fishy”
Freshwater mussels need a lot of luck to
successfully reproduce. Their unusual life
cycle begins when eggs held inside the
female are fertilized by sperm drawn
inside her while siphoning water. For
some, if a male of her kind isn’t nearby
upstream, she can’t reproduce. For a few,
this is not a problem because they seem
able to fertilize themselves.
Once fertilized, the eggs develop into a
larval stage inside the female before they
are released into the water to begin a
parasitic stage. With little time to waste,
these youngsters, called glochidia, must
attach themselves to a host fish or perish.
For some mussels, the host is limited to
only a few fish species. This generally
harmless parasitic stage lasts a matter of
weeks before the larvae transform into
young mussels and are ready to drop off
the fish and begin a life in the
stream bottom.
Built-in Fish Lure
To increase the chances of their young
making contact with a fish host, some
females “go fishing.” By displaying
specially adapted tissues that look like
fish prey, they try to lure fish to swim
near them. Sensing a fish nearby, the
female releases her young into the water,
ready to clamp onto the fish.
Mussel Aches
Our native freshwater mussels face
greater problems today than they did just
a few years ago. Some problems aren’t
new. Although water quality has improved
in some areas, pollution, especially
non-point source pollution, causes the
greatest threat to native mussels. Also
sedimentation continues to take a serious
toll. Habitat losses through channelization,
clearing of riparian and streambank
vegetation, dredging, and dam
construction still persist. Mussels are
impacted by loss of fish hosts from fish
kills or dams that prevent fish migration.
However, in some parts of the country,
it’s a non-native mussel causing the
most concern.
Zebra Mussel Invasion
In 1988, the first zebra mussels were
spotted in Lake St. Claire near Lake Erie
in Ohio. Assumed to be stowaways in the
ballast water of a trans-Atlantic ship,
this native of eastern Europe is now
widespread throughout waterways in
the eastern half of the United States.
Besides other problems, zebra mussels
have nearly eliminated native mussels in
some locations.
Unlike native mussels, the much smaller
zebra mussel (less than 2″ in length) does
not use a host animal in its life cycle, and
reproduces at a tremendous rate. They
can attach themselves to hard surfaces
with thread-like structures called byssal
threads. In zebra mussel-infested waters,
it is not unusual for native mussels to be
completely covered by zebra mussels.
Competition for food and oxygen weakens
and eventually starves native mussels.
They Lose, We Lose
Freshwater mussels have played a long
and varied role in people’s lives.Native
Americans used them for food, tools,
and jewelry. From about 1890 until the
invention of plastics around 1950, mussel
shells supported this country’s button
industry. More recently, the world’s
cultured pearl industry relies on implant
beads made from the superior shells of
North American mussels. In states where
mussel collecting is legal, harvesting
provides jobs and income to residents
along rivers.
Mussels have other values more difficult
to measure. In the rivers and lakes where
they live, their filtering ability makes
them natural water purifiers. They play
an important role in the aquatic food chain
as a food source for wildlife including
muskrats and otters.
Midden with Muskrat
They also can tell us something about the
health of the environment on which we
both depend. Mussels respond to changes
in water quality. Gradual mussel die-offs or
sudden mussel kills are reliable indicators
of water pollution problems and other
environmental health concerns. Stable,
diverse mussel populations generally
indicate clean water and a healthy aquatic
environment.
If we lose our freshwater mussels, we lose
more than a biological legacy unmatched
in the world. We lose a part of our cultural
heritage, we lose an economic resource,
and we lose an environmental health
maintenance and warning system.
Fortunately, there are efforts being
made to avoid these losses and things
everyone can do to help save our
freshwater mussels.
Mussels in our Future
Biologists from the U.S. Fish and Wildlife
Service (Service) and the U.S. Geological
Survey along with other Federal, State,
and private agencies are working together
to find solutions to problems facing our
mussels. These partners have developed a
National Strategy for the Conservation of
Freshwater Mussels, which will serve as a
blueprint for native mussel restoration.
Mussels and their habitats are being
surveyed, monitored and restored. The
Service’s endangered species program is
working to conserve these species and
their habitat. Some mussels facing
extinction in the wild have been removed
and brought to the Service’s National
Fish Hatcheries and State facilities for
safe-keeping. Hatcheries are developing
techniques for propagating rare mussels
for release. We are beginning to
reestablish mussel populations into
restored streams and rivers. The Service’s
Fishery Resources Offices help by
providing technical assistance on habitat
restoration and enhancement for mussels.
Aquarium and zoo personnel are also
assisting with conserving endangered
freshwater mussels through efforts such
as research and education programs. The
National Wildlife Federation has a long
history of working to enhance national
water quality and protect endangered
species through advocacy, education, and
on-the-ground programs. These efforts—
including the “Keep the Wild Alive”
campaign, which celebrates endangered
species protection efforts worldwide—
are helping to improve conditions for
imperiled freshwater mussels.But
there’s more that needs to be done and
you can help.
There are ways that you can help to
provide a secure future for mussels.
For instance, avoid contributing to water
pollution. Follow application directions
and don’t use fertilizers and pesticides
excessively. Leave stream sides vegetated
even if it means giving up part of the view.
Keep cattle and other livestock out of
streams. Report suspected pollution
problems to authorities. Get involved with
land use planning in your community.
In the long run, freshwater mussels will
benefit from improvements in water
quality. And so will you!
U.S. Fish & Wildlife Service
America’s Hidden Treasure
DiscoverFreshwaterMussels
They make no
sound.They cannot
see. Some may live
for decades, but
seldom move from
a secure spot. Yet,
freshwater mussels
are causing a stir,
becoming noticed
and making us
ponder their future
as we make plans
for our own.
Encrusted
Native Mussel
Buttons from
Days Past
Surveying Mussels
