抄録
Abstract: Laboratory experiments were carried out to observe the day/night activity patterns and habitat preferences of two gastropods, Gibbula umbilicaris and Jujubinus exasperatus, on leaves of the seagrass Posidonia oceanica. Both G. umbilicaris and J. exasperatus preferred old (apical) parts of leaves to young (basal) ones, and vertically oriented leaves rather than horizontal ones. Four types of behavior (rest, shaking epipedalic tentacles without any other motion, directional movements, and shell twisting mainly for foraging) were observed. Also, interspecific differences in the day/night activity pattern were recognized; G. umbilicaris mainly rested during the day and actively moved and foraged at night, whereas J. exasperatus continued to move about and forage during both day and night, resulting in a less marked day/night pattern. These results partly explain the observations of previous studies, in which both species were more abundantly sampled on seagrass leaves at night than by day.
