The burrows and physiological adaptations to a burrowing lifestyle of Natatolana borealis (Isopoda: Cirolanidae)

Abstract

The isopod Natatolana borealis Lilljeborg constructs U-shaped burrows in soft mud, the bore of which closely approximates the width of the occupant. Within artificial burrows, the isopods are largely quiescent and often adopt a position close to one of the burrow openings. Conditions within burrows constructed in the laboratory are moderately hypoxic [11.7 to 14.9 kPa (88 to 112 torr)], with isopods showing discontinuous irrigation behaviour (pleopod beating). Rates of oxygen consumption $(\dot M_{O_2 } )$ (measured at 10°C) are maintained approximately constant over a wide range of oxygen partial pressure (P_{O 2}) due, in part, to a pronounced increase in pleopod beat rate. Values for the “critical” partial pressure of oxygen (P_c), the P_{O 2} at which $\dot M_{O_2 }$ can no longer be maintained independent of P_{O 2}, were 2.0 to 3.3 kPa (15 to 25 torr). N. borealis can survive lengthy periods (65 h at 5°C) of anoxia, during which there is a significant reduction in the carbohydrate concentration and an increase in the l-lactate concentration of the tissues. The oxygencarrying capacity of the haemolymph of N. borealis was low. The haemocyanin showed a relatively high oxygen affinity [P₅₀=0.39 kPa (2.99 torr) at 10°C at the in vivo pH of 7.80] and a pronounced Bohr effect (-1.22). These characteristics may be advantageous to a burrowing mode of life and also for the conditions likely to be encountered in fish carcasses into which they burrow en masse to feed.