Fig. 2. The volume rates of ⁵¹Cr-EDTA clearance, urine flow, drinking and production of the final excretory product P by G. natalis either free ranging in the rainforest or after 6 days confinement in field enclosures. Clearance was determined over 6 days, and urine flow using the appropriate U:H ratio of ⁵¹Cr in the urine and haemolymph. Drinking and P production rates were determined on separate animals over a 24 h period after 6 days in the chambers described in the Materials and methods, which were held within the rainforest on Christmas Island. In the dry season, the crabs provided no urine at all and thus ⁵¹Cr measurements in the urine could not be made. The vertical arrows indicate the range of possible urine flow calculated using a U:H ratio of 1.04 from Greenaway (1994) or the values obtained from free-ranging and confined animals in the wet season. Values are means + S.E.M. (N=6–9). * indicates an effect of confinement compared with free-ranging crabs; indicates a difference between dry and wet season values; indicates that the animals confined during the dry season drank the entire volume of water provided and thus a minimum rate is available.

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