Seasonal and Diel Changes in Thermal Tolerance of the Crayfish Orconectes rusticus, with Evidence for Behavioral Thermoregulation

Abstract

The thermal tolerance (critical thermal maximum, CTM) of field-acclimatized Orconectes rusticus was examined on both a seasonal and diel basis. Seasonal changes in stream water temperature from 2.5 to 33.0°C caused a 10.8°C elevation (27.4 to 38.2°C) in mean CTM of adult O. rusticus. Juvenile O. rusticus exposed to a 6.9°C diel temperature change during summer altered their mean CTM by 1.2°C. Excessively high water temperatures (>39°C) in an isolated stream pool in southwestern Ohio during mid-July forced most O. rusticus to abandon the pool and dig burrows in sand and gravel beneath rocks near the shoreline. Mean water temperature in these burrows was >6°C cooler than that of the open pool. Orconectes rusticus physiologically adjusts its thermal tolerance to compensate for both seasonal and diel changes in its natural environment, but when temperatures change rapidly and become too high the species may search for or create cooler thermal refugia.