Abstract
The Ohta River flowing through Chugoku district empties with six branches into Hiroshima Bay situated in the northwest region of the Seto Inland Sea of Japan. The bottom fauna survey was conducted at stations established along a canal of the Ohta River and adjacent shallow marine area. A distinct transition of faunal composition was observed at a short distance between the river region and the sea out of the river mouth. In the canal, various taxonomic groups of brackish species and euryhaline ones of marine origin occurred, forming a very rich community. While, marine region in front of the river mouth harboured mainly polychaetes. The similarity analysis of community composition between sampling stations were highly suggestive of transverse formation of salt wedge. The faunal transition pattern was compared with those of the other rivers.
