The bottom sediment, benthic community, fish and larvae of commercial shellfish species were investigated at an artificial tidal flat in Mikawa Bay, Japan. Differences between low and high tidal flat areas were investigated. The central area of the development was comprised of fine sand, whereas fine sand and coarse sand were present in the original bottom of the tidal flat. Organic matter content was high in the waterway and the marginal area of the development. The water purification rate, in terms of macrobenthic biomass, was high in the central and marginal areas of the development. In contrast, biodiversity in terms of macrobenthos species abundance was low in the central area of the development. Thus the distributions in the water purification rate and biodiversity were different. Mactra chinensis, Mactra veneriformis, and Ruditapes philippinarum dominated the commercial bivalve species at different heights of the tidal flat. Platichthys bicoloratus dominated the fish larvae of commercial species, and distribution across defferent depths varied according to body length. The marginal area of the development was important for settling larvae. As distributions of dominant species and functions of the tidal flat are different, we suggest that it is important to ensure a range of consecutive depths when creating an artificial tidal flat.
