Effect of temperature on survival, intermolt period, and growth of juveniles of two mud crab species, Scylla paramamosain and Scylla serrata (Decapoda: Brachyura: Portunidae), under laboratory conditions

Temperature affects ectotherm's biological processes and plays a fundamental role in determining their geographical distribution. We elucidated the temperature adaptation of juveniles of two mud crab species in the genus Scylla De Haan, 1833 (in De Haan, 1833-1850): Scylla paramamosain Estampador, 1949 and Scylla serrata (Forskål, 1775), which occur mainly in temperate and subtropical/tropical areas in Japan, respectively. The first instar crabs (C1) were raised from three broods for each species and were individually cultured to molt to C2-C5 at different temperatures (15.2-30.5 °C℃). In S. paramamosain, C1 juveniles could molt to C2 at 15.4 °C and the survival rate was reduced at 29.8 °C through C4-C5. In S. serrata, C1 juveniles could not molt to C2 at 15.2 °C and the survival rate was not affected by temperature thereafter. The intermolt period was shortened at higher temperatures in both species. The carapace width of juveniles increased with increasing temperature but became smaller at 27.6-30.2 °C in S. paramamosain, whereas it appeared to reach a plateau at > 24 °C in S. serrata. The lower threshold temperature (95 % confidence interval) for the development of C1 juveniles was estimated as 13.65 °C (13.51-13.77 °C) for S. paramamosain, and 15.44 °C (15.12-15.72 °C) for S. serrata. Thus, juveniles of S. paramamosain and S. serrata adapted to lower and higher temperature conditions, respectively, reflecting their biogeographical distribution.