Seasonal Variations in O2-Consumption of Uca pugnax

1. Records of the O2-consumption of Uca pugnax were obtained during the summer, autumn, and winter months and analyzed for diurnal and lunar-day rhythms. 2. An apparent annual rhythm in mean rate of respiration is reported. 3. The respiratory rate during December, January, and February was found to be approximately 50% of that during June, July, and August. During September October, and November, a gradual decrease in rate was observed. 4. The form of the diurnal rhythm of respiratory rate showed no changes associated with time of year. Similarly, no seasonal changes in phase relations were observed. 5. The range of both diurnal and lunar-day rhythms showed fluctuations but these were not clearly associated with time of year. 6. The lunar-day rhythm was found to show changes as follows : June through September the curve was bimodal with maxima at lunar zenith and nadir; beginning in October and continuing through January the curve was unimodal with a maximum near lunar zenith; in February the curve was bimodal but with minima at lunar zenith and nadir. 7. The unimodal curve of the transitional period is interpreted as being the resultant curve of a mixed population. 8. The possible relationship of exogenous factors to these seasonal variations is discussed.