Physiological acclimation to decreased water temperature and the relative importance of water viscosity in determining the feeding performance of larvae of a serpulid polychaete

Ambient temperature exerts both physiological and mechanical effects on the rates of functional processes of small aquatic ectotherms. Physiological effects of temperature result from its influence on the rates of chemical reactions. Mechanical effects of temperature result from the inverse relationship between the temperature of water and its dynamic viscosity. We measured the relative importance of these components of temperature on the feeding performance of polychaete larvae. Cohorts of larvae were reared for 24 h at 20°C and 10°C in treatments where the physiological and mechanical effects of these temperatures were separated. The feeding performance of these larvae was subsequently measured in treatments where these components of temperature were similarly partitioned. Cold-reared larvae displayed complete acclimation of feeding performance to the physiological effects of decreased temperature: thus, increased viscosity was responsible for 100% of the difference in feeding performance between 20°C and 10°C. The physiological ability of small aquatic ectotherms to acclimate functional processes to temperature variation may be greater than previously thought, and these results have implications for understanding the responses of aquatic ectotherms’ to global temperature change.