Sediment characteristics are key factors influencing the nature of tidal flat ecosystems. Although sedimentary strength would be one of the important sedimentological properties for the colonization of benthic communities, little is yet known of it.
　We conducted field experiments in an natural tidal flat (Banzu) in Tokyo Bay, Japan, and a constructed tidal flat (Nishiura) in Mikawa Bay, Japan, to obtain the data of sedimentary strength (cone resistance) by the Cone Penetration Test (CPT) and to investigate relationships between the cone resistance and other physical parameters including granulometry and topography. We also collected the data of the cone resistance and macrofaunal densities from the Intertidal Flat Experimental Facility (IFEF) in the Port and Harbour Research Institute to examine the influence of macrofauna on the cone resistance of the IFEFsediments.
　For the natural intertidal sediments, spatial variability in the cone resistance values was large although temporal variability in those was small. The cone resistance values for the natural intertidal sediments correlated with elevation or silt/clay content. For the created tidal flat, the cone resistance values increased over time due to the sediment compaction by external forces. The strength in the created tidal flat was also stimulated with the fall of the interstitial water table accompanied by topographical changes. The results of the data from the IFEF showed that not only physical factors but also biological factors affect sedimentary strength. Bioturbation by infauna would avoid the sediment compaction by external forces.