Vertical movement of the littoral fringe periwinkle Nodilittorina exigua in relation to wave height

The relationship between daily vertical distribution of the littoral fringe periwinkle Nodilittorina exigua and daily wave height was investigated at Shirahama, Japan (33°42N; 135°21E) daily, from May 1981 to August 1982. The positions of the snails on a cliff shore were high when the wave-reach was high, and ascended with increasing height of the wave-reach. The snails moved a long distance upwards in late summer, when typhoon swells occurred, and moved gradually downwards again in autumn, parallel to decreasing wave-reach. They displayed more active vertical movement in warmer seasons of the year and this activity was not positively correlated with the frequency of wetting. Downward migration in autumn ensured frequent and constant immersion. Taken in conjunction with results in the literature, the present study emphasizes the adaptive significance of vertical movement by N. exigua in the littoral-fringe environment.