Life History and Stable Regeneration of the Endangered Saltmarsh Sesarmid Crab Clistocoeloma Sinense in Small Populations of the Isolated Metapopulation of Tokyo Bay, Japan

The saltmarsh sesarmid crab, Clistocoeloma sinense, inhabits the muddy substrata in upper intertidal saltmarshes, and is designated as endangered in Japan. Seasonal changes were investigated in population characters, including abundance, time to sexual maturity, reproductive season, and recruitment of juveniles in a regional metapopulation in Tokyo Bay. Crab samples were collected monthly at five small isolated habitats along the coast of the bay from July, 2011, to March, 2013. Ovigerous females were found during summer in a single peak, and a peak of juvenile recruitment occurred in autumn. Size distribution analysis indicates that growth is slower than for other saltmarsh crab species and life span is at least 4 years. Females reach maturity when they enter the second breeding season following recruitment. The slow growth and reclusive behavior of C. sinense may be closely related to the characteristics of its habitat which is under buried stones or wood in the uppermost part of intertidal muddy substrata. Recruitment of juveniles and the presence of breeding females were observed at all five study sites located along the Tokyo Bay coastline, suggesting that each population stably regenerates by larval settlement following larval dispersal and growth in the water column in Tokyo Bay. These data suggest that an increase in the number of small muddy flats with intertidal salt marsh vegetation along the coastline may be the most effective measure to conserve the Tokyo Bay regional metapopulation of this crab species.