Sediment compositions were clarified in local, limited and perennial eelgrass Zostera marina colonies along the coast of Seto Inland Sea, by comparison of the sediment compositions of the sandy bottom between colony and adjacent bare ground. In colonies, it was observed not only 1cm over of thickness in sandy layer above rhizome of Z. marina plants, but also a pebble and oyster shell layer below the sandy layer. On the other hand, in bare ground, there was no pebble and oyster shell layer or the sandy layer above rhizome was very thin. This forms useful data for the development measures for the design of artificial tidal flats and sandy shallow bottom areas containing the restoration ground for sea grass beds. Necessity of suitable sediment composition was recognized in thickness of sandy layer above the rhizome, and arrangement of a pebble and/or oyster shell layer below rhizome of the eelgrass plants.
