Feeding, respiration, and aerial exposure in a scavenging cirolanid isopod from New Zealand

Abstract

The feeding rate, oxygen consumption, and effects of aerial exposure were measured for a cirolanid isopod, Natatolana rossi, collected from a shallow subtidal habitat at Kaikoura, New Zealand. The isopod survived 7 days exposure in water-saturated air at 15°C and mean survival time was similar both in water-saturated air (5.1 days) and water (4.6 days) at I°C. Weight loss in aerial conditions increased both with time and with decreasing relative humidity (RH). Weight-specific transpiration rates (mg water loss h-1 mg-1 wet wt) were 0.057 for 60% RH and 0.017 at 80% RH. Lethal water loss was approximately 30% of the initial wet weight. Weight-specific rates of resting oxygen consumption for N. rossi were low compared with other aquatic peracarids (0.26 μl O1 mg-1 h-1) at the habitat temperature of 10°C. Oxygen uptake increased with exposure temperatures between 5 and 25°C. Following aerial exposure, oxygen uptake was significantly reduced to 50% of the aquatic rate and was temperature-independent. Feeding experiments using blue moki fish (Latridopsis ciliaris) showed that N. rossi is unable to feed in air and that food intake in aquatic conditions increased with exposure temperature. Highest food consumption was measured at 15°C, where the rate represented 30% of the dry body weight per day. This study suggests that N. rossi is a 'sit and wait, batch reactor' predator/scavenger. It displays a low resting metabolism and is capable of long periods of fasting. It maximizes food intake with a high feeding rate on an energy-rich food source. In addition, its ability to survive aerial exposure would allow it to survive and minimize energy expenditure if inadvertently displaced into intertidal habitats.