Following to urbanization of shore areas in Tokyo Bay, about 90% of tidal flats including salt-marshes have been landfilled, and their remaining became isolated from each other. Thus, populations of salt marsh-dependent species have shrunk or have become extinct. We report partial population structure of the endangered salt-marsh crab Clistocoeloma sinense that occurred in small salt-marshes along the coast of Tokyo Bay.

Field survey was carried out in 8 sites with salt-marsh vegetation along the coast of Tokyo Bay in 2011. We collected all crabs found in a belt transect (2x50m) during 1 hr in each sites. Carapace width (CW) of each collected was measured with a hand caliper.

Number of collected crabs and their mean CW were largely varied among the sites. Numbers of crabs in Tamasaki and Shinhama lagoon were significantly larger than other sites. The CWs in Yatsu and Edo river were significantly larger than those of other sites.

Tokyo Bay is the northernmost distribution area of C. sinense. The small partial populations of the crab found in this study suggest that they may be maintained under bay-scale metapopulation network. Furthermore, Tamasaki and Shinhama lagoon where keeping larger populations are regarded as important habitats for source populations in Tokyo Bay. We also discuss the connectivity of the populations of each site in the bay, based on results of genetic analyses.