Persistent tidal and diurnal rhythms of locomotory activity and oxygen consumption in Emerita asiatica (M.-EDW.)

Abstract

1. The oxygen consumption of the sand crab, Emerita asiatica, when estimated employing solitary specimens showed an unmistakable persistent tidal rhythm. 2. Numbers of 4 and 5 crabs even when huddled together in the respiration chambers showed the rhythmicity in their metabolic rates indicating mutual synchronisation of individual oscillations. 3. In newly moult crabs, in spite of the intensified level of metabolism accompanying the process of moulting, the tidal rhythms were displayed in the metabolic rates. 4. Simultaneous estimations of the swimming activity employing a vertically moving cage device and the oxygen consumption of individual crabs further confirmed the persistence of rhythms. 5. The activity of Emerita coinciding with the high tide at night was considerably enhanced. It was clear that this exaggerated nightly activity was due to the superimposition of a diurnal rhythm an a tidal rhythm. 6. The rhythms in the locomotory activity waned after the crabs had been in the laboratory for 3–4 days. 7. The behaviour of Emerita, as seen in the activity records and oxygen consumption estimations made in the present study, is reminiscent of its behaviour in nature relative to the tide. 8. The adaptive significance of such rhythmic behaviour to the continued existence of littoral animals is evident.