The effects of photoperiod and temperature on embryonic diapause termination in the hermit crab Pagurus nigrofascia

: The intertidal hermit crab Pagurus nigrofascia reproduces in March in Fukuoka, Japan. The embryos remain in diapause until October, begin to develop in November, and most broods hatch in December. This study examined the effects of photoperiod and temperature on embryonic diapause termination (EDT) in both laboratory and field condi -tions. Females with diapause eggs were maintained in the laboratory under three different photoperiod/temperature re -gimes: constant (14L/10D, 22° C), decreasing photoperiod condition (from 12L/12D to 9.8L/14.2D, 22 °C), and decreasing temperature condition (14L/10D, from 22 °C to 10° C). The EDT date was compared among four groups: the above three experimental groups and the field group. The dates at which > 50% of females possessed eggs after the EDT were November 10 (constant), October 30 (decreasing photoperiod), September 27 (decreasing temperature), and November 4 (field). The mean duration until EDT was 82 days (constant), 67 days (decreasing photoperiod), and 36 days (decreasing temperature). Diapause was significantly shorter under both the decreasing photoperiod and the decreasing temperature conditions compared to the constant. Thus, EDT was strongly affected by temperature but weakly altered by photope riod. This study is the first to report the influence of photoperiod and temperature on EDT in decapod crustaceans.