Abstract
Spatial distributions of bivalves and gastropods on the mud flat of Isahaya Bay, western Kyushu, were studied. In Isahaya Bay, a vast expanse of mud flat (3, 550ha) was closed off from the Ariake Sea on April 14, 1997, by the construction of a dike for reclamation. Since that time, it has been possible to walk on the dried mud flat and see the numerous dead shells exposed by the reduction of the mud surface. The spatial distribution of each species is as follows. 1) Tegillarca granosa was very dense (>30 ind./m2) at the lower part of the dried mud flat, ca. 1 to 2km from the former mean high water point of the spring tide (MHWS). 2) Cerithideopsilla djadjariensis, Tellina (Moerella) iridescens and Estellacar olivacea were distributed at the middle part of the dried mud flat, ca. 0.5 to 1km from the former MHWS. 3) Glauconome chinensis was especially dense at the uppermost part of the dried mud flat near the former MHWS and ranged as far as the former mean high water of neap tide (MHWN). These facts suggest that there were three separate zones of mollusks arranged parallel to the water level on the tidal mud flat of Isahaya Bay.
