2013 年 67 巻 2 号 p. 56-63
The reproductive ecology of the victorious moon crab Matuta victor (Matutidae, Brachyura, Crustacea) was surveyed on an open sandy beach of the Genkai-nada Sea in Nata, Fukuoka City, Japan, between June, 2008, and October, 2009. Crabs were collected in the shallow subtidal zone (<50 cm depth) during daytime by hand or with hand nets and the condition of their gonads and embryos was checked. Large-sized M. victor, including juveniles and adults with a carapace width (CW) of >17 mm were present only from May to October on this beach, and they probably migrated elsewhere between November and April. CW frequency distributions showed a clear sexual distinction: females were composed of juveniles (17.9–31.8 mm CW) and adults with mature exoskeleton (31.7–44.6 mm CW), but males (21.6–56.8 mm CW) included adults of >41.9 mm CW showing gonadal development. Ovigerous females were observed between late May and early September. Embryonic development indicated that eggs were spawned mostly between May and August and that they hatched between July and September. Ovigerous adults showed no gonadal development, and this suggests that females oviposit only once in one reproductive season. In both sexes, gonads markedly developed between May and July and regressed after August. In sum, in the Genkai-nada Sea, adults of M. victor appear to inhabit the shallow subtidal zone between early summer and autumn and reproduce sparingly in summer, spawning only once within one reproductive season. Confirmation of the whereabouts and reproductive state of the crabs during the colder months is essential to comprehend the complete reproductive ecology of M. victor in the temperate zone.
