Spectacle case pearly mussel

Spectacle case pearly mussel
Mature and young Cumberlandia monodonta.
Conservation status
Endangered  (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Order:	Unionoida
Family:	Margaritiferidae
Genus:	Cumberlandia
Species:	C. monodonta
Binomial name
Cumberlandia monodonta (Say, 1829)
Synonyms
Margaritifera monodonta Say, 1829

The spectacle case pearly mussel or spectacle case (Cumberlandia monodonta) is a species of bivalve in the Margaritiferidae family. It is endemic to the United States. The spectaclecase is a freshwater mussel that the U.S. Fish and Wildlife Service listed as an endangered species.

Historically, the spectaclecase was found in at least 44 streams of the Mississippi, Ohio and Missouri River basins in 14 states. It has been extirpated from 3 states and today is found in only 20 streams. The spectaclecase’s current range includes Alabama, Arkansas, Illinois, Iowa, Kentucky, Minnesota, Missouri, Tennessee, Virginia, West Virginia, and Wisconsin. With few exceptions, spectaclecase populations are fragmented and restricted to short stream reaches.

Spectaclecase mussels are found in large rivers where they live in areas sheltered from the main force of the river current. This species often clusters in firm mud and in sheltered areas, such as beneath rock slabs, between boulders and even under tree roots.

Dams:

Population losses due to dams have contributed more to the decline and potential extinction of the spectaclecase than any other factor. Dams affect both upstream and downstream populations by disrupting seasonal flow patterns, scouring river bottoms, changing water temperatures and eliminating river habitat. Large rivers throughout nearly all of the spectaclecase mussel’s range have been dammed, leaving short, isolated patches of habitat between dams. Spectaclecase mussels likely depend on a fish species, or other aquatic species, to move upstream.

Because dams block fish passage, mussels are also prevented from moving upstream. This isolates upstream populations from those downstream, leading to small, unstable populations, which are more likely to die out.

Small Population Size and Fragmentation:

Most remaining populations of spectaclecase are small and geographically isolated. Small populations remaining in short sections of rivers are susceptible to extirpation from single catastrophic events, such as a toxic spill. Also, this level of isolation makes natural repopulation of areas that once supported mussels impossible without human intervention.

Sedimentation:

Poor land use practices, dredging, intensive timber harvests, highway construction, and other activities accelerate erosion and increase sedimentation. Sediment that blankets a river bottom can suffocate mussels since they cannot move to avoid the impact. Also, large amounts of sediment in the water column reduce the ability of mussels to remove food and oxygen, which can lead to reduced growth, reproduction and survival.

Pollution:

Adult mussels are easily harmed by toxins and degraded water quality from pollution because they are sedentary (they tend to stay in one place). Pollution may come from specific, identifiable locations such as accidental spills, factory discharges, sewage treatment plants and landfills, or from diffuse sources like runoff from fields, feedlots, mines, construction sites and roads.

Contaminants may directly kill mussels, but they may also indirectly harm spectaclecase by reducing water quality, affecting the ability of surviving mussels to reproduce and lowering the numbers of host fish.

Channelization:

Dredging and channelization have profoundly altered riverine habitats nationwide. Channelization physically changes streams by accelerating erosion, reducing depths, decreasing habitat diversity, destabilizing stream bottoms and removing riparian vegetation.

Nonnative Species:

The invasion of the nonnative zebra mussel into the United States poses a serious threat to native mussels. Zebra mussels proliferate in such high numbers that they use up food resources. They attach to native mussel shells in such large numbers that the native mussel cannot open its shell to eat or breath.

Sources

• Mollusc Specialist Group 2000. Cumberlandia monodonta. 2006 IUCN Red List of Threatened Species. Downloaded on 6 August 2007.

• https://www.fws.gov/midwest/endangered/clams/spectaclecase/SpectaclecaseFactSheetMarch2012.html