Impacts of Seasonal Thermal Stress on Energetics of Popenaias popeii (Texas hornshell)

Abstract

Texas hornshell (Popenaias popeii) is a federally endangered mussel occurring in Texas, New Mexico, and Mexico. We examined temperature effects on energetic costs of feeding, and on scope for growth: the net energy balance available for reproduction and growth. Mussels were acclimated to experimental temperatures for ≥ 2 week and then subjected to energetic assays (i.e. respiration rate, clearance rate, and assimilation efficiency). Energetic costs of feeding and digestion were greatest at lowest (16℃) and highest (32℃) temperatures tested, but negligible at intermediate temperatures (20℃). Scope for growth peaked at 28℃ and rapidly fell as temperatures increased from 28 to 32℃. Riverine temperature profiles suggest that the primary growing season is in early summer and early fall, with declining surplus energy in mid-summer. Flow regulations to help minimize unfavorable temperatures during mid-summer may be critical for the long-term survival of this species.