ACTIVITY RHYTHM OF THE SEA-PEN, CAVERNULARIA OBESA VALENCIENNES, UNDER TEMPERATURE AND LIGHT CYCLES

Abstract

Circadian rhythms are generally known to be entrained to light cycles, and in some poikilothermic animals living in terrestrial region also to temperature cycles. The entraining effect of temperature cycles may be attributable to the fact that the daily fluctuation of temperature on the land is rather clear and regular closely related to the natural light change. On the other hand, the daily fluctuation of temperature in the sea is not so clear as in the terrestrial region, being generally very small or perfectly null depending on the depth. So, it is interesting to examine the effect of temperature cycle on the circadian rhythm of marine organisms, to make it clear whether the effect of temperature cycle is dependent on species, or generally seen on the circadian rhythms of different species of poikilothermic animals. The author made an experiment concerning this problem in a series of experiments with using of the sea-pen, Cavernularia obesa, a marine colonial coelenterate living on the sand bottom of shallow water, and obtained data somewhat unclear with difference among colonies in behavior under the temperature cycle (Imafuku, 1973). Thus, he repeated the experiment on the same species, recording its behavior continuously for about four months through under temperature cycles of various levels of temperature, and also examining the effect of light cycle.