Effects of Hypoxia and Thermal Stress on a Rare Freshwater Mussel (Order: Unionida) in Relation to Sympatric and Allopatric Mussel Species

Abstract

Pleurobema riddellii is proposed for federal listing as threatened. Remaining populations are largest in Texas and Louisiana. Respirometry was used to compare effects of temperature on hypoxia sensitivity of P. riddellii with sympatric and allopatric species. No detectable effect of temperature on hypoxia sensitivity was observed in P. riddellii under the conditions tested. Interspecific variation in ability to regulate respiration rate as dissolved oxygen declined was greater at 25°C than at 32°C. Pleurobema riddellii exhibited a lower critical thermal maximum and a steeper metabolic response to temperature than a widespread, sympatric species, Cyclonaias pustulosa. Behavioral responses to thermal stress varied among species and generally occurred near upper tolerance limits. Evaluating species-specific physiological responses to stressors is critical for assessing whether protective thresholds for mussels are suitable across species within a local community or region, or whether thresholds should be developed for individual species. This is particularly important considering climate change.