Critical thermal maxima of two species of intertidal crabs, Scylla olivacea and Thalamita crenata at different acclimation temperatures

Abstract

Understanding the thermal tolerance of both candidate and potential aquaculture species is important for determining their temperature limit at certain stages of culture. The aim of the present work was to determine the effect of acclimation at different temperatures on the Critical Thermal Maxima (CTMax) and escaping temperature (Tesc) and Acclimation Response Ratio (ARR) of the mud crab, Scylla olivacea, and the crenate swimming crab, Thalamita crenata. Immature crabs (N = 135) were acclimatized at three temperatures of 24 °C, 28 °C and 32 °C and CTMax was measured after an acclimation period of one week and re-acclimation of at least three weeks. An increase in CTMax increased the mean escaping temperature (Tesc) for both crabs, and was within the range of their CTMax value. Only a few crabs tried to escape during the CTMax test in which the Tesc were 39.85 °C to 40.25 °C and 37.52 °C–38.21 °C for S. olivacea (n = 12) and T. crenata (n = 22), respectively. The CTMax of S. olivacea ranged from 40.03 °C to 43.39 °C, while the CTMax for T. crenata ranged from 37.11 °C to 42.42 °C, and both increased directly with temperature. Results obtained in the present study indicated that S. olivacea crabs were more tolerant to increased temperature than T. crenata, suggesting that S. olivacea is better adapted to high environmental temperature conditions.