Tidal and Diurnal Rhythms of Locomotory Activity in Carcinus Maenas (L.)

ABSTRACT Spontaneous locomotory activity was recorded continuously for several days in Carcinus maenas (L.). A complex rhythm was observed which could be analysed into two components, one of diurnal frequency (24 hr.), with peaks of activity during the hours of darkness, and one of tidal frequency (ca. 12·4 hr.), with peaks at the time of high tide. The rhythms persist in constant dim light at constant temperatures, whether the crabs are kept moist in air or continuously immersed in sea water. The resultant effect of the two rhythms is to produce particularly high activity peaks during periods which recur with a semi-lunar frequency. Experimental results relate to observed behaviour on the shore.