To understand more fully the larval dispersal and settlement of the snow crab Chionoecetes opilio in natural habitats, we tested the effects of temperatures ranging from ∼1-20°C and ∼1-18°C on the survival and developmental period of snow crab larvae in the zoeal and megalopal stages, respectively, through laboratory experiments. The survival rates of second zoeae and megalopae were significantly greater at 5-16°C and 5-14°C, respectively. There were no statistically significant differences among the survival rates of megalopae reared at 3-16°C, although greater survival rates were observed at 5-14°C. The mean numbers of days from hatching to second zoeae and megalopae and from megalopae to reach first crab instar were significantly shorter at warmer temperatures. Moreover, the relationships between mean temperatures and larval periods were well described by the heat summation theory equations. The threshold temperatures for larval development were estimated to be-2.24-0.63°C
they decreased with larval development as an adaptation for deeper vertical distributions in later larval stages. On the basis of larval distribution with respect to water temperature in natural habitats as well as the heat summation theory equations, the entire larval duration from hatching to first crab instar was estimated to be 74.4-123.4 days, which is similar to that in natural habitats inferred on the basis of the time lags in the occurrence of peak abundance between each larval stage.