Thermal biology of the sub-polar–temperate estuarine crab Hemigrapsus crenulatus (Crustacea: Decapoda: Varunidae)

Optimum temperatures can be measured through aerobic scope, preferred temperatures or growth. A complete thermal window, including optimum, transition (Pejus) and critical temperatures (CT), can be described if preferred temperatures and CT are defined. The crustacean Hemigrapsus crenulatus was used as a model species to evaluate the effect of acclimation temperature on: (i) thermal preference and width of thermal window, (ii) respiratory metabolism, and (iii) haemolymph proteins. Dependant on acclimation temperature, preferred temperature was between 11.8°C and 25.2°C while CT was found between a minimum of 2.7°C (CT(min)) and a maximum of 35.9°C (CT(max)). These data and data from tropical and temperate crustaceans were compared to examine the association between environmental temperature and thermal tolerance. Temperate species have a CT(max) limit around 35°C that corresponded with the low CT(max) limit of tropical species (34–36°C). Tropical species showed a CT(min) limit around 9°C similar to the maximum CT(min) of temperate species (5–6°C). The maximum CT(min) of deep sea species that occur in cold environments (2.5°C) matched the low CT(min) values (3.2°C) of temperate species. Results also indicate that the energy required to activate the enzyme complex (Ei) involved in respiratory metabolism of ectotherms changes along the latitudinal gradient of temperature.