Effects of Acute Thermal Stress on Texas Hornshell Mussel (Popenaias popeii)

Abstract

Extreme weather conditions are placing increasing stress on aquatic ectotherms in the southern U.S. We investigated effects of thermal stress on the federally endangered Texas Hornshell (Popenaias popeii), the last freshwater mussel species in New Mexico. Using a combination of physiological assays, we examined effects of rapid temperature changes on scope for growth (SFG: energy surplus for growth and reproduction) and absolute aerobic scope (AAS: respiratory capacity in excess of that needed for basic maintenance). At the enzymatic level, respiratory capacity patterns differed from those of a previously examined ectotherm (marine shrimp), rendering estimates of AAS of minimal use in assessing thermal stress of Texas Hornshell. At the organismal level, diurnal changes in temperature typical of the summer months had a significant, negative impact on scope for growth. Maintaining sufficient daily flows during the hot summer months may be critical for the long-term survival of this species in New Mexico.