島根県大橋川におけるホトトギスガイ（Arcuatula senhousia Benson）個体群の空間分布とその時間的変化

抄録

We examined the spatial and temporal changes in percent cover of the Arcuatula senhousia Benson (Mytilidae, Bivalvia) population by SCUBA diving in the brackish Ohashi-River in Shimane Prefecture, southwestern Japan. From spring to summer, the numbers of A. senhousia increased, and the mussel mats spread from the deep, central part of the river to the shallower river banks. In summer, the mats spread over the entire transect line, but in late summer and autumn, the mats reduced in the deep central part. The factors that induced the decrease of population were different every year; they included low salinity, low dissolved oxygen, high water temperature, flood (physical destruction) and the combination of these. The seasonal pattern of population dynamics of A. senhousia in the Ohashi-River was closely related to the riverbed topography as well as seasonal trends in salinity and dissolved oxygen of river water.