Ionic regulation in crustacea: the influence of temperature on apparent set points

1. Homeostatic set points have usually been neglected in discussions of temperature effects on ionic regulation. 2. Using published data for crustacean haemolymph on Na+, Cl−, freezing point depression and conductivity, this paper explores the effects of temperature on iso-ionic and isosmotic concentrations and on concentrations representing particularly effective hyper-regulation. 3. It is argued that these concentrations approximate to set points, though the exact nature of the regulated variable(s) is unclear. 4. As temperature increases most of these concentrations stay constant or fall slightly; none rises or falls by more than 2%/°C. 5. The few available data on K+, Ca2+ and Mg2+ are considered briefly