Unionid mussels are considered sensitive to salinity and there is growing concern in arid and semi-arid regions that declining flows coupled with anthropogenic impacts are amplifying natural salinity levels. In this study, we tested the effects of varying salinity concentrations (3.0, 4.0, 5.0, 6.0, 7.0 and 10.0 ppt NaCl) on survival of adult Popenaias popeii, (Texas Hornshell). This species occurs in the Rio Grande basin of Texas and northern Mexico, an arid to semi-arid stream plagued by salinization, and was recently listed as Endangered under the U.S. Endangered Species Act. We performed 2, 4, and 10-day toxicity tests on individuals from two disjunct populations: Laredo, TX, and the Lower Canyons of the Rio Grande near Big Bend National Park. We found no significant differences in LC50 estimates between populations at 96-hrs or 10-days but significant differences in TUD50s at 5 ppt between populations, which indicates that tolerance does not vary but sensitivity may between these populations. Overlaying LC50 estimates at 10-days for both populations on plots of salinity (ppt) measured over time, we show parts of the Rio Grande periodically approach or exceed 4.0 ppt, indicating these reaches are becoming unsuitable for P. popeii and populations within them at risk.

人们认为紫苏贻贝对盐分敏感，在干旱和半干旱地区，人们日益关注流量的下降以及人为的影响正在加剧自然盐分的水平。在这项研究中，我们测试了不同盐度浓度（3.0、4.0、5.0、6.0、7.0和10.0 ppt NaCl）对成年Popenaias popeii存活的影响，（得克萨斯州Hornshell）。该物种发生在得克萨斯州的里奥格兰德盆地和墨西哥北部，是受盐碱化困扰的干旱至半干旱河流，最近被美国《濒危物种法》列为“濒危物种”。我们对两个不同种群的个体进行了2天，4天和10天的毒性测试：德克萨斯州拉雷多和大弯国家公园附近的里奥格兰德下峡谷。我们发现在96小时或10天时，人群之间的LC50估计值无显着差异，而人群之间在5 ppt时TUD50的显着差异，这表明耐受性没有变化，但这些人群之间的敏感性可能不同。随时间测量的盐度（ppt）图覆盖了两个种群在10天时的LC50估计值，我们显示，里奥格兰德州的部分地区会定期接近或超过4.0个百分点，P. popeii和其中的种群处于危险之中。