Thermal Tolerance and Mortality of the Texas Pigtoe (Fusconaia askewi) Under Experimental Conditions

Systemic habitat destruction over the last 100 years combined with major anthropogenic stressors such as aquatic contaminants, exotic species, and economic endeavors is driving the decline in freshwater unionid species diversity. Global temperatures continue to increase, with January 2024 being the warmest on record according to the latest report by the World Meteorological Organization. Freshwater mussels play a crucial role in aquatic ecosystems, contributing significantly to benthic processes in rivers and streams, yet they remain highly sensitive to environmental changes. This study specifically investigates the thermal tolerance of the Texas pigtoe (Fusconaia askewi) under elevated temperature conditions and explores the implications for developing effective conservation strategies in freshwater ecosystems. Eighty-four individual adult Texas pigtoe mussels were collected from the upper Sabine River near Hawkins, Texas, and taken to the University of Texas at Tyler to evaluate the effects of elevated temperature, a likely factor impacting mussels in East Texas. In the thermal tolerance study presented here, 100% survival occurred at both the control (20 °C) and the 25 °C test points. The 30 °C treatment group had an overall mortality of 14% and the 35 °C treatment group showed a mortality rate of 43% by the end of the trial, suggesting the typical summer temperatures in Texas streams will result in the loss of a portion of an otherwise healthy population.