Air breathing by the purple shore crab, Hemigrapsus nudus (Dana). 4. Aquatic hypoxia as an impetus for emersion? Oxygen uptake, respiratory gas transport, and acid-base state
Blood gas and acid-base status in the purple shore crab, Hemigrapsus nudus (Dana), was determined before, during, and after 3 h of exposure to water with a PO sub(2) of 20 mmHg. The ventilatory, circulatory, and O sub(2) uptake responses were assessed during progressive hypoxia to a PO sub(2) of 5 m...
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| Published in: | Physiological zoology 1996-07, Vol.69 (4), p.864-886 |
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| Main Authors: | , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Blood gas and acid-base status in the purple shore crab, Hemigrapsus nudus (Dana), was determined before, during, and after 3 h of exposure to water with a PO sub(2) of 20 mmHg. The ventilatory, circulatory, and O sub(2) uptake responses were assessed during progressive hypoxia to a PO sub(2) of 5 mmHg. The respiratory rate was independent of PO sub(2) to 10 mmHg and was achieved by increasing cardiac output rather than hyperventilation or tachycardia. In contrast to the respiratory alkalosis seen in most other hypoxic crustaceans, Hemigrapsus exhibited a large and rapid metabolic alkalosis within 30 min of exposure to water with a PO sub(2) of 20 mmHg. Subsequently, there was a smaller respiratory alkalosis so that by 3 h of elapsed time haemolymph pH had increased to a pH of 8.19. Return to normoxia prompted an almost immediate removal of both the respiratory and metabolic alkaloses. There was no evidence of any anaerobiosis. A small increase in circulating urate toward the end of the exposure period ( similar to 0.05 mmol/L super(1) maximum) suggested that O sub(2) use by urate oxidase might be limiting. Urate accumulation in Hemigrapsus was shown to be temperature-dependent. Exposure to 20 mmHg PO sub(2) induced decreases in both arterial and venous O sub(2) pressure and content, while O sub(2) delivery was maintained, as was an arterial-venous difference. Fitting the in vivo data to O sub(2) equilibrium curves indicated increased haemocyanin O sub(2) affinity due to the alkalosis and increased urate, which served to maintain arterial oxygenation near 100%. Oxygen delivery switched from a reliance on dissolved O sub(2), in normoxic water to a dependency on haemocyanin O sub(2) transport. The apparent perfusion-based compensation for reduced O sub(2) availability, the rapid metabolic alkalosis, and the ability, of the haemocyanin in Hemigrapsus remain unusually, well oxygenated are features quite different from those reported for other species of similar habit and habitat. This strongly implies that Hemigrapsus is well adapted to hypoxic exposure and that avoidance of hypoxic water is not a stimulus for this crab to assume air breathing. The role of aquatic hypoxia as a selective pressure in crustaceans evolving to life on land must be questioned. |
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| ISSN: | 0031-935X 1937-4267 |