Seasonal and tidal-height variations in body weight and radular length in Nodilittorina radiata (Eydoux & Souleyet, 1852)

Seasonal and tidal height variations in tissue weight and radular length of Nodilittorina radiata (Gastropoda: Littorinidae) were investigated for 14 months on a concrete breakwater at Kattoshi, Hokkaido, northern Japan. Snails were collected monthly from high, mid and low zones on the break-water. The regressions of dry tissue weight and radular length against shell height were determined monthly in each tidal zone. From spring to early summer, tissue weight in the low and mid zones increased more than in the high zone. During summer, tissue weight in the low and mid zones declined. After a small increase in autumn, tissue weight decreased until early spring in all zones, and was higher in the high and mid zones than in the low zone. Radular length increased from autumn to spring in all zones and then decreased during summer, particularly in the low zone. The variations in tissue weight and radular length are discussed in relation to temporal and spatial variations in snail activities, particularly feeding, and environmental variables.