ABSTRACT
Locomotor activity has been continuously recorded by aktograph in Carcinus maenas (L.), using (a) ‘dock crabs’ from non-tidal docks, and (b) ‘shore crabs’ from the intertidal zone.
Dock crabs, kept in continuous light, either dim or bright, show a temperature-independent rhythm. During the first 24 hr. large peaks occur after dusk and just before dawn, with smaller peaks during the day. Each daytime peak occurs about 12–13 hr. later than a night peak. Subsequently all the peaks drift, occurring about 50 min. later each day.
Dock crabs kept in a day/night light regime do not show this drift.
Shore crabs, after 4–8 weeks in non-tidal aquaria, behave in the same way as dock crabs.
It is suggested that the drifting of the peaks represents an expression of endogenous tidal rhythmicity and a ‘multiple clock’ hypothesis is postulated to account for the control of rhythmicity.
