2021 年 50 巻 p. 17-27
We investigated the seasonal variability in fecundity and egg size in a Petrolisthes japonicus population by monthly sampling for one year on an intertidal cobble and boulder shore on the Boso Peninsula, Japan. Fecundity (number of eggs per brood) was determined for ovigerous females with non-eyed or eyed eggs in early (May and June), middle (July) and late (August and September) breeding periods. The long and short diameters of non-eyed eggs were measured, and the egg volume was calculated. Fecundity was positively correlated with female body size and found to be greater in the middle breeding period than in the early and late breeding periods. Egg loss occurred during embryogenesis, the egg loss rate being calculated as 44.6%, 14.8% and 30.2% from the non-eyed to the eyed egg stages in the early, middle and late breeding periods, respectively. Egg size decreased linearly from the early to the late breeding periods. It is inferred that the seasonal variability in reproductive output, fecundity and egg size in P. japonicus may be regulated by female nutritional conditions and seasonal fluctuations of food production for larvae, as well as a trade-off between the number and size of eggs in a brood.
