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Table 2.

The osmotic pressure and concentration of major ions in the haemolymph and urine of Gecarcoidea natalis in the rainforest during the dry season (June 1997)

Haemolymph
Urine
Confined
Confined
Free rangingDrinking waterNo drinking waterFree rangingDrinking waterNo drinking water
Osmotic pressure (mOsm) 805.8±12.9W 696.0±22.5W, * 734.9±13.9W, * 834.8±21.7 722.1±9.7W, * 738.8±9.3W, * 
Na (mmol l−1482.8±15.9W 396.5±17.7W, * 453.8±13.7W 488.8±22.1W 429.5±8.1W, * 440.9±18.4W, * 
K (mmol l−19.7±0.2W 8.1±0.4W 9.0±0.2W 8.0±0.9 8.1±1.1 7.8±2.0 
Mg (mmol l−111.4±0.5W 8.8±0.5W, * 9.2±0.2W, * 13.2±0.2W,  11.6±0.6W, * 10.6±2.5W, * 
Cl (mmol l−1328.7±13.4 297.0±10.1 319.0±8.3 370.3±20.2W,  348.9±11.5W,  298.5±66.1W 
Ca (mmol l−121.6±0.4W 17.9±0.7 20.9±0.7W 6.6±2.1  16.6±2.3 * 16.0±4.9 * 
Haemolymph
Urine
Confined
Confined
Free rangingDrinking waterNo drinking waterFree rangingDrinking waterNo drinking water
Osmotic pressure (mOsm) 805.8±12.9W 696.0±22.5W, * 734.9±13.9W, * 834.8±21.7 722.1±9.7W, * 738.8±9.3W, * 
Na (mmol l−1482.8±15.9W 396.5±17.7W, * 453.8±13.7W 488.8±22.1W 429.5±8.1W, * 440.9±18.4W, * 
K (mmol l−19.7±0.2W 8.1±0.4W 9.0±0.2W 8.0±0.9 8.1±1.1 7.8±2.0 
Mg (mmol l−111.4±0.5W 8.8±0.5W, * 9.2±0.2W, * 13.2±0.2W,  11.6±0.6W, * 10.6±2.5W, * 
Cl (mmol l−1328.7±13.4 297.0±10.1 319.0±8.3 370.3±20.2W,  348.9±11.5W,  298.5±66.1W 
Ca (mmol l−121.6±0.4W 17.9±0.7 20.9±0.7W 6.6±2.1  16.6±2.3 * 16.0±4.9 * 

Crabs were either free ranging in the rainforest or one of two groups held confined within enclosures in the rainforest. One of the confined groups was provided with drinking water and the other was dependent on water naturally available within the enclosures. The enclosures were open at the top and allowed crabs contact with the forest floor. Values are means ± s.e.m. (N=8-12 in each group).

*

, significantly different to free-ranging crabs at P<0.05;

, urine significantly different to haemolymph at P<0.05;

, effect of including drinking water; W, different to corresponding value for free-ranging or confined crabs in the preceding wet season - see Table 1.

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