Japan Sea National Fisheries Research Institute, Niigata 951-8121, Japan
Diel movements were observed and compared for three herbivorous gastropods, Turbo cornutus, Omphalius pfeifferi carpenteri and Astralium haematragum, which dominate the shallow rocky coasts of the Japan Sea. Experiments were conducted under 12L-12D conditions using a very high sensitivity ICCD television camera. T. cornutus was more active in dark than light conditions, and moved at a speed of 8-11cm/min. The distance moved and time spent moving per 24 hours were 37-39m and 7 hours, respectively. O. pfeifferi carpenteri also showed a more active habit in dark conditions, and moved at a speed of 2-5cm/min with the distance of 5-13m and time of 3-6 hours per 24 hours. In contrast to the two species, A. haematragum did not show any diurnal rhythm. It moved at a rather slow speed of 1-2cm/min with the distance of 0.8-2.6m and time of 1.5-4 hours per 24 hours. The behavioral significance of these three species was discussed, particularly in connection with predators.