A day in the life of an isopod: Time and energy allocations in the semiterrestrial Ligia pallasii

Daily time and energy budgets were calculated for a population of Ligia pal lasii on the west coast of British Columbia, Canada. A time budget was dete rmined from direct observation of field animals. Equivalent energy costs fo r each activity were determined from oxygen uptake (V-O2) measurements on a nimals engaged in the same activity in a laboratory respirometer. Activitie s measured included feeding, resting, walking, running, molting, and brood- carrying. The least energy-demanding activity in the field was resting (0.5 6 J.250-mg indiv(-1).h(-1)). The most costly activities were feeding and ru nning (1.36 and 1.31 J.250-mg indiv(-1).h(-1), respectively). Walking incre ased energy expenditure by 50% over resting levels (by 28 J.250-mg indiv(-1 ).h(-1)). Molting (0.96 J.250-mg indiv(-1).h(-1)) and brood-carrying (0.57 J.250-mg indiv(-1).h(-1)) costs were determined for laboratory animals but were not observed in the field population. The most energy-demanding period of the day for these nocturnal isopods was just after dusk and at dawn, wh en locomotory activity was most intense. Energy cost for 24 hours was 13.9 J.250-mg indiv(-1). This energy could be met by consumption of 11 mg scaven ged seaweed, requiring about 35 min of the daily time budget.