Temperature tolerance of juveniles of two mud crab species, Scylla paramamosain and Scylla serrata (Decapoda: Brachyura: Portunidae)

Temperature is one of the most important environmental factors affecting the geographic distribution of ectotherms. We evaluated the low- and high-temperature tolerance limits of juveniles of two mud crab species, Scylla paramamosain and Scylla serrata, which are distributed in temperate and subtropical/tropical areas in Japan, respectively. Experiments were performed twice for S. paramamosain and four times for S. serrata using laboratory-raised juveniles. The juveniles were stocked in small containers, and the temperature was reduced or raised by 1°C every 24 h. The critical low or high temperatures (CLT or CHT) were estimated as the temperatures at which 50% of test juveniles ceased walking behaviour or died. The estimated CLT values for walking and survival were summarised as 8.4±0.7°C (mean±standard deviation) and 6.4±0.9°C in S. paramamosain and 9.6±0.6°C and 7.4±0.4°C in S. serrata, respectively. The CHT for walking could not be estimated, as almost all surviving juveniles exhibited walking behaviour, whereas the estimated CHT values for survival were summarised as 39.0±0.4°C in S. paramamosain and 39.1±0.6°C in S. serrata. Thus, interspecific variation in low-temperature adaptation was evident, and S. paramamosain are adapted to the lower-temperature environment.