Tidal current patterns and seabed sediment distribution at a sill in Sasebo Bay, Japan

Abstract Sasebo Bay, located in western Kyushu, Japan, is a semi-enclosed coastal bay with a seabed that supports a rich ecosystem. The importance of near-bed hydrodynamic conditions for the distribution of bivalves in Sasebo Bay has been suggested, but the detailed spatial characteristics remain unclear. In this study, we estimated the lunar semi-diurnal (M2) tidal current in the southern region of Sasebo Bay, where a sill and tidal channels are present, using shipboard current measurements conducted during 23 cruises between 2016 and 2025. The results show that the spatial variations in the M2 current are strongly affected by the sill and channel topography. In addition, we found a significant correlation between the M2 peak bed shear stress and the median grain size of the seabed sediments. The findings confirmed a close association among hydrodynamic conditions, seabed sedimentary characteristics, and the benthic biological environment in coastal areas.