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 1°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. Weightspecific rates of resting oxygen consumption for N. rossi were low compared with other aquatic peracarids (0.26 μl O2 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.The Isopoda is a diverse crustacean group, members of which have exploited a range of marine, fresh-water, and terrestrial habitats. They are predominantly opportunistic omnivores with some members specializing in carnivory, scavenging, or parasitism (Schram, 1986). In contrast with other isopods, cirolanid isopods are specialized macrophagous feeders which can be predators on fish, polychaetes, and amphipods as well as carrion feeders. Commonly known as sea-lice, these isopods are reported to cause extensive damage to fishes caught in nets and long lines (Hale, 1927;Bruce, 1986).Recently, there have been a number of studies on the population biology, reproduction, and physiology of the cirolanid Natatolana borealis Lilljeborg from deep-water habitats. However, there are no comparative data on the energetics and metabolism of shallow-water species. The present study is part of a larger investigation into the ecophysiology of cirolanids from New Zealand and concentrates on Natatolana rossi (Miers), which is frequently found in nets and baited traps. I investigated the effects of aerial exposure on feeding and respiration of N. rossi, including the effects of temperature on oxygen uptake. For the feeding studies, isopods were provided with blue moki, a commercial fish thought to be especially susceptible to damage...

Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships

“…This strategy, and scavenging, as seen in Cirolanidae, would seem to be the plesiomorphic strategy within this clade. Some species of Natatolana are scavengers and will enter baited traps (Arntz and Gutt 1999;Marsden 1999;Storch et al 2002). Cirolanid diversity is higher in tropical than cooler regions (Bruce 1986;Keable 1995) and correlates with a more diverse food supply, exemplified by the diversity of a typical food source: fishes.…”

Ventilation rate and behavioural responses of two species of intertidal goby (Pisces: Gobiidae) at extremes of environmental temperature

“…Nilsson et al (2004) found the coral dwelling goby Gobiodon histrio able to withstand 3 h of air exposure. Marsden (1999) demonstrated that the cirolanid isopod, Natatolana rossi, is capable of extended periods of aerial exposure and suggested that this adaptation is a possible response to inadvertent displacement into intertidal habitats. An examination of either their relative ability to find water of better quality or amphibious activity may be informative, as it seems that thermal tolerance alone is insufficient to explain the vertical zonation patterns exhibited by these intertidal fishes.…”

First report of the scavenging isopod Natatolana neglecta (Crustacea: Isopoda: Cirolanidae) feeding on a sea turtle

“…Isopods of the family Cirolanidae are distributed worldwide, including marine, estuarine and some freshwater environments (Bruce et al, 2002). Some cirolanids are micro-predators on the surface of fishes or invertebrates (Bruce, 1986;Brusca et al, 1995), other species are scavengers on marine fauna with no apparent preference for particular carrion types (Stepien & Brusca, 1985;Bruce, 1986;Berrow, 1994;Keable, 1995;Wong & Moore, 1995, Marsden, 1999. For some species it is not clear if they are only scavengers or also predators (Bunkley- Williams & Williams, 1998).…”