A DAY IN THE LIFE OF AN ISOPOD: TIME AND ENERGY ALLOCATIONS IN THE SEMITERRESTRIAL LIGIA PALLASII

ABSTRACT

Daily time and energy budgets were calculated for a population of Ligia pallasii on the west coast of British Columbia, Canada. A time budget was determined from direct observation of field animals. Equivalent energy costs for each activity were determined from oxygen uptake (V_O2,) measurements on animals engaged in the same activity in a laboratory respirometer. Activities measured included feeding, resting, walking, running, molting, and brood-carrying. The least energy-demanding activity in the field was resting (0.56 J · 250-mg indiv¹ · h⁻¹). The most costly activities were feeding and running (1.36 and 1.31 J · 250-mg indiv⁻¹ · h⁻¹, respectively). Walking increased 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, when 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 scavenged seaweed, requiring about 35 min of the daily time budget.