Variation in Embryonic Temperature Sensitivity among Groups of the Sea Urchin, Hemicentrotus pulcherrimus, which Differ in their Habitats

The sea urchin, Hemicentrotus pulcherrimus, spawns during winter and spring in Kagoshima, Aomori and Kanagawa. The seawater temperature during the spawning season ranges from about 16 to 19°C at Sendai, Kagoshima, from about 12 to 15°C at Misaki, Kanagawa, and from about 5 to 7°C in Mutsu Bay, Aomori. Among the groups of this species differing in their habitats, optimal temperature ranges for development were found to differ significantly and the difference corresponded to the difference in seawater temperature during the spawning season. Despite the difference in the optimal temperature range for development among the groups, the relationship between developmental speed and temperature within the common optimal temperature range for these groups was nearly constant.The thermotolerance of embryos produced by cross-fertilization between the group from Kagoshima and that from Aomori was also examined. These embryos showed maternal inheritance of embryonic thermotolerance.