抄録
Seasonal migration and activity patterns of Nodilittorina radiata (Eydoux & Souleyet) (Gastropoda: Littorinidae) were investigated by observations of marked snails and transect sampling on a concrete breakwater at Kattoshi, Hakodate Bay, northern Japan. Snails were classified into two size groups, large (≥5mm in shell height, mature) and small (≤4mm, immature) . Marked snails of both groups started descending into the intertidal zone in early summer, and they ascended into the supratidal zone in autumn. The locomotory activity of both groups was high during the summer and low during the winter. For both size groups, the proportion of snails in the intertidal zone was high during the summer and low during the winter. Since the seasonal migration and activity patterns were similar for both large (mature) and small (immature) snails, animals evidently undertake seasonal vertical migrations not only for reproduction, but also for other reasons such as food and refuge from environmental stress.
