Distribution of snow crab, Chionoecetes spp., larvae off Wakasa Bay in the Sea of Japan

抄録

The distribution of snow crab, Chionoecetes spp., larvae was studied by horizontal plankton net tows using a multiple opening/closing nets and environmental sensing system from the surface to the bottom off Wakasa Bay (approx. 500 m) in the Sea of Japan. The hatching season was concluded to occur between early February and late April with a peak occurring in March. First zoeae occurred most densely in March, second zoeae in April, and megalopas between April and June within the Tsushima Warm Current (0-200 m). The temperature of the strata at which more than 88% of each stage of larvae were distributed varied from 8.4 to 15.0°C. As the larval stage progressed, they gradually moved to deeper water strata. In and after June, megalopas observed in the premolt stage started a downward migration beyond the thermocline to the cold bottom water (water proper to the Sea of Japan, <5°C all year round). Therefore, the settlement of megalopas and metamorphosis to the first benthic stage was concluded to occur in June. The second zoeae and megalopas underwent diurnal vertical migrations. The durations of the first and second zoeal stages and the megalopal stage were estimated at approximately 20 days, 20 days, and 60 days, respectively.