Abstract: Fecundity of the Japanese mitten crab Eriocheir japonica was investigated at Tsuyazaki Beach, Fukuoka Prefecture, Japan. The numbers of eggs and hatched larvae counted in the laboratory were com bined and categorized by the number of ovipositions. When the number of oviposition could not be directly counted, it was estimated based on the appearance of the egg mass. The fecundity increased with increasing carapace width(CW)and decreased in the later ovipositions. It was estimated to range from120, 000(40mm in CW)to600, 000(70mm)in the first oviposition, 80, 000to300, 000in the second one and20, 000to80, 000in the third one. Females oviposit up to three times within one reproductive season and die without further moulting. Considering the energetic cost of migration, it may be more profitable to consume all accumulated energy within one reproductive season, and spawn many offspring while they are not ex hausted just after migration. Potential lifetime fecundity can be estimated from the total fecundity; it ranged from230, 000(40mm in CW)to980, 000(70mm). When compared to other marine grapsid crabs, maturity size and fecundity of the first oviposition of E. japonica are both larger, but the regression line describing the CW-fecundity relationship is similar to those of other grapsid crabs. Large fecundity per brood with large maturity size compensates for the decrease in their brooding time and lifetime fecundity.

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Abstract: The reproductive cycle of the protandric shrimp Pandalus latirostris in Saroma Lagoon, Hokkaido, was examined morphologically and histologically. The pleopod morphotypes showed that this population comprised five groups that were in different sexual development stages during the study period. The sexual groups were related with body size and roughly represented year classes. Gonadal development was divided into 11 stages by observing germ cell development. Seasonal changes of gonadal development were examined for the three dominant sexual groups. In Saroma Lagoon, males generally matured at Age-1 and mated as female at≥ Age-2. Some males thought to be Age-0matured as males once again or changed sex at Age-1. Individuals that matured as males in two consecutive years were also observed in gonadal development of normal males and reached sizes of typical females, probably at Age-2. Values of both gonadsomatic and vas deferens-somatic indexes rapidly increased from July and showed their lowest values in September. Male and female mature germ cells were observed from late August to late September, suggesting that the breeding season occurs in autumn and lasts one month.

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Abstract: The breeding patterns of three interstitial harpacticoid copepods, Stenocaris intermedia(Cylindropsyllidae), Tetragoniceps sp.(Tetragonicipitidae), and Phyllopodopsyllus sp.(Tetragonicipitidae)were surveyed in Otsuchi Bay, northeastern Japan.Among the three species, Phyllopodopsyllus sp. had the smallest clutch size and the largest eggs and it bred over the longest period, whereas larger clutch sizes, smaller eggs, and shorter breeding periods were typical of the other two species. Breeding season also varied among species; Stenocaris intermedia and Tetragoniceps sp. bred during the cold season, whereas ovigerous females of Phyllopodopsyllus sp. were observed during the warm season.

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Abstract: Energy budgets in Neptunea arthritica, a species with significantly different proportions of assimilated energy directed to reproduction in males and females, were estimated based on sex ratio(male: female), assimilated energy and energy allocation in each age class, and seasonal changes in density. The sex ratio changed with every sample, but the energy budgets in year-classes were framed using the interpolated mean ratio of0.95during the period of density measurements. The several observed energy budget patterns in the neptune whelk very nearly corresponded to the growth stages of hatchling, immature, and adult. The biomass in the hatchling fraction of the population did not increase very much regardless of relatively high assimilation at that stage, because of the rather heavy mortality as compared with recruitment. In contrast, in the immature fraction, final biomass increased considerably as compared with the initial state, as the result of high assimilation and growth with little mortality. Finally, in the adult fraction, biomass substantially decreased from the initial to final state due to assimilation only roughly equalling initial biomass, or falling short of doing so, thus resulting in little or no growth, and to mortality being roughly equal to or exceeding assimilation. The turnover ratio of the neptune whelk population in the investigation period showed a very low value of0.42, reflecting a drastic mortality in the older adult population. The energy budget patterns in the three growth stages and the migration pattern in immatures suggest that construction of a nursery ground for immature individuals should be a very important consid eration in efforts to propagate the neptune whelk.

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Abstract: Reproductive characters and the population structure of the subtidal hermit crab, Pagurus ochotensis Brandt, 1851are described, based on samples collected from Akkeshi Bay, eastern Hokkaido, Japan from April 1998to September 1999. Crab abundance increased markedly in June 1998, and became small after May 1999.Ovigerous females were observed from March to September, and male precopulatory guarding behavior of ovigerous females was observed in June and July, suggesting that some crabs may have two or more clutches a year. Smaller females bred earlier than larger females. This variation in the timing of breeding might be explained either as anadaptation to or as being determined by environmental or physiological constraints.

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