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Long-term changes in unionid assemblages in the Rio Grande, one of the World's top 10 rivers at risk


A.Y. Karatayev, Great Lakes Center, Buffalo State College, 1300 Elmwood Avenue, Buffalo, NY 14222, USA. E-mail:


  1. According to the World Wildlife Fund, the Rio Grande is the most endangered river system in the North American continent and one of the World's top 10 rivers at risk, but is globally important for freshwater biodiversity. Unionid bivalves of the Rio Grande river basin used to be represented by a unique assemblage, including four endemic species (Truncilla cognata, Potamilis metnecktayi, Popenaias popeii, and Quadrula couchiana); however, surveys from 1998–2001 failed to recover any live endemic unionid species suggesting a sharp decrease in their populations and potential of extinction.
  2. Intensive surveys (162 sites sampled) conducted by the authors from 2001–2011 on the Rio Grande and its tributaries in Texas recovered live T. cognata, P. metnecktayi, and the largest population of P. popeii ever reported. Overall the unionid assemblage of the Rio Grande basin has changed considerably during the last century.
  3. Decline in species diversity, range fragmentation, local extirpations, and introduction of widespread common species were documented. Two species (Q. couchiana and Quincuncina mitchelli) are locally extinct. Potamilus metnecktayi and T. cognata have been extirpated from the Pecos River and their ranges in the Rio Grande have been reduced. Popenaias popeii has been extirpated from the Pecos River and Las Moras Creek along with the reduction and fragmentation of its range in the Devils River and Rio Grande.
  4. Among the environmental factors responsible for the degradation of unionid assemblages in the Rio Grande river basin, the most important are impoundments, habitat degradation, salinization, pollution, and over-extraction of water.

Copyright © 2012 John Wiley & Sons, Ltd.

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