Thermal tolerance of Popenais popeii (Texas Hornshell), an endangered freshwater mussel endemic to the Rio Grande basin

Authors: Jennifer Khan, Amanda Goldsmith, Michael Hart, Charles Randklev

Year: 2019

Abstract

Freshwater mussels are among the most imperiled groups of aquatic organisms in North America largely due to anthropogenic impacts, such as altered temperature regimes. Detailed knowledge on lethal temperatures for freshwater mussels has been limited to only 22 species, which is less than 10% of the species known to occur in North America, and relatively little is known about the thermal tolerance of mussel species inhabiting arid or semi-arid river systems. This lack of information is problematic because climate change coupled with increasing human water demand is expected to increase the frequency and intensity of droughts in these regions, which may negatively impact threatened mussel populations. To determine the effects of elevated water temperature on vulnerable mussel populations, we tested the upper thermal tolerances of the larval (glochidia) and juvenile life stages of Popenaias popeii (Texas Hornshell) from the Devils River, a species recently listed as Endangered under the U.S. Endangered Species Act. Mussels were acclimated to 27°C across a range of experimental temperatures (30 – 38 °C) in standard acute laboratory tests. The median lethal temperature (LT50) among populations in 24-h tests with glochidia averaged 32.0 °C and ranged from 31.1 to 32.7 °C. The LT50 in 96-h juvenile trials was 32.7 °C. Ongoing thermal trials will test P. popeii throughout its range in the Rio Grande basin.