1970 年 20 巻 3 号 p. 115-119
Along the northern coast, the peninsula borders the neck of the Ariake Sea. As the western half of the coast is rocky and is connected with the East China Sea through the strait, the rising tide of the open sea flows straightly toward the tip of the peninsula, but the eastern half is sandy and is fed by the drainage of the River Midori at its end. The chlorine-content of the sea water decreases toward the east and abruptly falls near the eastern extremity owing to dilution by the river water. As the northern half of Yatsushiro Bay is almost separated from the open sea by the Amakusa Islands and receives the water from the Kuma River, the chlorine-content of the sea water is also considerably low. Along the northern coast, the Gloiopeltis furcata-Sargassum thunbergii community is remarkable in the western half and the Enteromorpha compressa-Gracilaria verrucosa community in the eastern half. At the eastern extremity Caloglossa leprieurii grows in the muddy marsh which is separated from the sea and invaded by sea water only at high tide, but on the coast of Yatsushiro Bay it grows on the muddy shore of the bay. Along the coast of this bay, Enteromorpha compressa and Gracilaria verrucosa are generally dominant, but only a small community of Sargassum thunbergii survives around a small island near the western extremity of the bay where sea water flows from the harbour of Misumi. In the intertidal zone of Misumi, three belts are recognized which are named after their dominant species. They are from above downwards ; Gloiopeltis furcata-Monostroma nitidum belt, Ulva pertusa-Sargassum thunbergii belt and Sargassum patens belt. As the sand is deposited on the bottom of the sea toward the east, where the depth becomes shallower the community gradually changes and the lowest belt is lost first, and at last the uppermost belt is replaced by that of Enteromorpha compressa-Gracilaria verrucosa. The change of these communities is considered to be caused by the fall of salinity of sea water.