Mollusk Guide:
Fifty-one species of freshwater mussels have or previously had historic ranges is Texas. Of these fifty-one mussels, twenty of them are listed federally or by the state of Texas as threatened or endangered.
In North America, they are considered the most endangered of animals. 67 percent of North American mussel species are considered threatened. A major cause of the decline is excessive sedimentation caused by poor land- use practices.
In general, five major contributors to the loss of freshwater biodiversity are: pollution, sedimentation, flow modification, exotic species invasions, habitat modification and destruction, and over-exploitation. Climate change can create smaller and more isolated populations susceptible to extinction.
Texas Pimpleback
Quadrula petrina
Listed as threatened by State of Texas, the Texas Pimpleback is a candidate for being federally listed as endangered. The last live specimens were encountered in 2004 in the San Marcos River, near the confluence of the Blanco River. Known to occur in the lower Blanco River as late as 1977, however surveys in the 1990’s failed to find any evidence of continued survival.
False Spike
Quadrula mitchelli
The False Spike is listed as threatened by State of Texas. Two populations are known historically in Texas. The Rio Grande population declined prior to major European impacts: observed in Central Texas 1931. Droughts and floods in Central Texas in the late 1970’s and early 1980’s appear to have largely eliminated this species and none have been found alive since.
Asian Clam
Corbicula
The Corbicula is known as Asian Clam. It was first reported in 1774 as an invasive species. The exact method of introduction to Texas is unknown. The Corbicula is in all major river systems in Texas. This clam tolerates a wide variety of habitats including substrates of fine silt, mud, sand gravel, cobble and bedrock and spawns twice in the summer.
Texas Fatmucket
Lampsilis bracteata
The Texas Fatmucket mollusk is a threatened species found in several streams and rivers throughout Texas, including the four counties that comprise the Blanco basin. Here habitat is limited to gravel substrates including broken bedrock and coarse gravel in moderately flowing water (figure 25). Because the Fatmucket cannot tolerate impediments like dams and very slowmoving water, available habitat within the basin is limited and must be carefully managed to maintain flow and water quality (suspended solids and sediment loading), as well as substrate scouring rates.
Mussels Life Cycle
Blanco Water Atlas 