Thermal preference of the common brown shrimp (Crangon crangon, L.) determined by the acute and gravitational method

Temperature is of critical importance for ectotherms, having vast impacts on physiology, behavior and distribution. In many species, however, the behavioral component of temperature selection is not well understood. This study addresses the thermoregulatory behavior of the common brown shrimp (Crangon crangon, L.), which is a central component of the Wadden Sea ecosystem and an important fishery resource of high commercial value. To investigate whether brown shrimp are thermosensitive and perform behavioral thermoregulation, we examined the short- and long-term thermoregulatory behavior by using the acute and gravitational method for temperature preference testing. For the acute method, female adult brown shrimp were acclimated to 5 temperatures between 9 °C and 19 °C for two weeks. For the gravitational method, the shrimp were acclimated to 3 temperatures within the same range. Hereafter, thermal preferenda were determined in an annular shaped preference chamber. Acute and gravitational thermal preference experiments revealed brown shrimp to be thermosensitive and perform behavioral thermoregulation. Using the acute method, a positive correlation of acclimation and preferred temperature was observed, resulting in a final thermal preferendum of 15.9 °C. In experiments using the gravitational method, preference temperature was heavily modulated by the photoperiod, with brown shrimp selecting temperatures more precisely during the scotophase than the photophase. Determined at dark exclusively, however, no effect of acclimation temperature on gravitational preference after 24 and 48 h was observed. Preferenda ranged between 13.5-15.0 °C after 24 h and 12.0-14.9 °C after 48 h, respectively, and no significant differences between both methods were detected. Based on these findings, 20-24 h of gradient exposure can be considered sufficient to obtain thermal preferenda that are unaffected by the animal's prior thermal history. Thermal preferenda determined in the present study were higher than the average temperature experienced by brown shrimp in the field. Still, thermal preferenda were considerably lower than previously reported optimum temperatures for brown shrimp.