Alleged rhythm in phototaxis synchronous with ocean tides

Abstract

A series of observations upon the periwinkles, Littorina litorea and Littorina rudis, and the snail, Ilyanassa obsoleta, carried on from June 18 until August 26, failed to corroborate the conclusions of Bohn, 1 who describes a daily rhythm in the reaction to light in specimens of Littorina litorea and Littorina rudis corresponding to the times of high and low tide, even when the animals are taken from the sea and placed in aquaria, exhibiting thus a sort of “memory” of the tides.

In the present experiments the reaction to light was tested in each specimen, at least three times a day, and white and black screens were used, as in Bohn's experiments, to determine whether the forms were positively or negatively phototactic. During the days of June, they were, as a rule, negatively phototactic, and as night approached, they became positively phototactic. However, after July 18, the preponderance of positive phototaxis during the day was very noticeable. This period of transition corresponded to the time of change from spring to neap tide, during which the specimens out on the rocks were exhibiting a corresponding change in phototaxis, for the water did not reach them; their behavior tallied with the description of Mitsikuri, 2 who showed that when desiccated, periwinkles became positively phototactic, and when wet, turned negatively phototactic. In these observations there is an approach to Bohn's conclusions concerning rhythms in phototaxis with respect to fortnightly (spring and neap) rhythms in tides, if not to his conclusions concerning daily (high and low) oscillations.