The endogenous locomotor activity rhythm of four supralittoral peracarid crustace

The ‘strength’ of the endogenous locomotor activity rhythm of four peracarid crustacean species, denned by the precision and persistence of the rhythm, was examined with particular reference to a ‘burrowing’ versus epifaunal supralittoral life-style. The ‘strength’ of the endogenous component of the activity rhythm was also illustrated using a modified periodogram analysis. In all species, the talitrid amphipods Talitrus saltator, Talorchestia deshayesi, Orchestra gammarella and the oniscoid isopod Ligia oceanica, the laboratory-monitored rhythm and the field emergence pattern displayed a nocturnal, circadian pattern with no clear evidence of any circa-tidal influence. The precision and particularly the persistence of the rhythm of the sand-shore burrowing species T. saltator and T. deshayesi are especially well developed, although a ‘strong’ endogenous component is present in the rhythm of all four species. The significance of the endogenous locomotor rhythms is considered with respect to the supralittoral ecology of the species.