U.S. Fish & Wildlife Service
Rayed Bean (freshwater mussel)
The rayed bean is a freshwater
mussel that the U.S. Fish and
Wildlife Service has proposed to list
as an endangered species.
Endangered species are animals and
plants that are in danger of becoming
extinct. Threatened species are
animals and plants that are likely to
become endangered in the
foreseeable future. Identifying,
protecting, and restoring
endangered and threatened species
are primary objectives of the U.S.
Photo by USFWS
Fish and Wildlife Service’s
endangered species program.
What is the Rayed Bean?
The rayed bean, a small freshwater mussel of the upper Midwest and Eastern
Appearance: The rayed bean is a United States, has been proposed for listing as an endangered species.
small freshwater mussel, usually
less than 1.5 inches long. Its shell is
smooth-textured and green, but they are sometimes found in of a specific host fish species to
yellowish-green, or brown with large rivers and wave-washed areas complete development into juvenile
numerous dark-green wavy lines. of glacial lakes, including Lake Erie. mussels. If successfully attached to
The male’s shell shape is generally They prefer gravel or sand a host fish, glochidia mature into
elongated, whereas the female’s is substrates, and are often found in juvenile mussels within a few weeks.
smaller and elliptical. and around roots of aquatic They then drop from the fish and
vegetation. continue to grow, if they fall onto
Range: The rayed bean historically appropriate substrate. Using fish as
was found across a wide expanse Adults spend their entire lives a host species allows the rayed bean
that included parts of the Midwest, partially or completely buried in to move upstream and populate
the eastern United States, and north substrate, filtering water through habitats it could not reach otherwise.
to Ontario, Canada. Once found in at their gills to remove algae, bacteria,
least 112 streams, canals, and lakes, detritus, microscopic animals, and What threatens the rayed bean
the rayed bean now occurs in only 28 dissolved organic material for food. mussel?
streams and 1 lake; a 75 percent Dams: Dams affect both upstream
reduction in the number of occupied Reproduction: The life cycle of the and downstream mussel populations
streams and lakes. The species has rayed bean, like most freshwater by disrupting natural river flow
been extirpated from Illinois, mussels, is unusual and complex. patterns, scouring river bottoms,
Kentucky, Tennessee, and Virginia The male releases sperm into the changing water temperatures, and
but is still found in Indiana, water column that is then siphoned eliminating habitat. The rayed bean,
Michigan, New York, Ohio, by the female to fertilize her eggs. a mussel adapted to living in flowing
Pennsylvania, West Virginia and Fertilized eggs develop into water habitat, cannot survive in the
Ontario, Canada. microscopic larvae, called glochidia, still water impounded behind dams.
within special gill chambers. Female
Habitat: The rayed bean generally mussels expel mature glochidia, The rayed bean also depends on host
lives in smaller, headwater creeks, which must attach to the gills or fins fish as a means to move upstream.
Because dams block fish passage, sedimentation also reduces feeding planning for recovery and recovery
mussels are also prevented from and respiratory ability for the actions.
moving upstream, which isolates snuffbox mussel, which can lead to
upstream mussel populations from decreased growth, reproduction, and Watershed Protection through
downstream populations leading to survival. Partnerships: The rayed bean
small unstable populations more cannot survive without help from
likely to die out. Nonnative Species: Nonnative zebra watershed partnerships to restore
mussels have invaded U.S. waters, habitat and improve surface lands.
Pollution: Adult mussels are easily and pose a serious threat. Zebra Causes of habitat degradation are
harmed by toxins and degraded mussels proliferate in such high numerous in streams throughout its
water quality from pollution because numbers that they use up food range. In many cases, the threats
they are sedentary (they tend to stay resources and attach to native are not from actions in or adjacent to
in one place). Pollution may come mussel shells in such large numbers the rivers where the species is
from specific, identifiable sources that the native mussel cannot eat or found. Instead, threats are due to
such as accidental spills, factory breath. widespread problems on uplands at
discharges, sewage treatment plants the highest elevations of watersheds.
and solid waste disposal sites or Another invasive species, the round Habitat restoration will require
from diffuse sources like runoff goby, is a nonnative fish that may improvements across the entire
from cultivated fields, pastures, displace native host fish species, watershed. The voluntary assistance
feedlots, farms, mines, construction thus reducing reproductive ability of of Federal and State agencies,
sites, private wastewater discharges, the snuffbox reproduce. conservation groups, local
and roads. Contaminants may governments, private landowners,
directly kill mussels, but they may industries, businesses, and farming
What is being done to conserve and communities will be necessary to
also reduce water quality, affect the restore snuffbox mussels?
ability of surviving mussels to have meet recovery goals.
young, or result in lower numbers or Listing: In 2004, the U.S. Fish and
disappearance of host fish. Wildlife Service designated the What can you do?
rayed bean mussel as a candidate
Learn more about how the
Sedimentation: Sedimentation can species for listing as threatened or
destruction of habitat leads to loss
be accelerated by poor land use endangered under the Endangered
of endangered and threatened
practices, dredging, impoundments, Species Act. The Service is now
species and our nation’s plant and
intensive timber harvesting, and proposing to list it as endangered. If
animal diversity. Discuss with
heavy recreational use. Excessive listed, the rayed bean will receive
others what you have learned.
sedimentation suffocates freshwater the full protection of the Endangered
mussels because it is difficult for Species Act (ESA). The ESA would
Help improve water quality locally
them to move away from the threat. provide protection against certain
in streams by minimizing use of
Impacts from increased or heavy practices and would require
lawn-care chemicals and properly
disposing of or recycling hazard-
ous materials found in your home,
like batteries, paint, car oil, and
When boating, please follow any
rules established to prevent the
spread of exotic pests like the
Join a conservation group or
volunteer at a local nature center,
zoo, or wildlife refuge.
U.S. Fish & Wildlife Service
1 Federal Drive
Fort Snelling, Minnesota 55111