Air breathing by the purple shore crab, Hemigrapsus nudus (Dana). 2. Respiratory gas and acid-base status in response to emersion
Respiratory gas transport, acid-base state, and ionic status of Hemigrapsus nudus before, during, and after 24 h of emersion from 10 degree C water were determined in the laboratory at two air temperatures (10 degree and 25 degree C). These data were compared to those from animals sampled in situ on...
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| Published in: | Physiological zoology 1996-07, Vol.69 (4), p.806-838 |
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| Main Authors: | , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Respiratory gas transport, acid-base state, and ionic status of Hemigrapsus nudus before, during, and after 24 h of emersion from 10 degree C water were determined in the laboratory at two air temperatures (10 degree and 25 degree C). These data were compared to those from animals sampled in situ on the shore. During the initial 30 min, H. nudus exhibited an internal hypercapnic hypoxia. The arterial O sub(2) content decreased from 0.69 mmol/L to a mean 0.43 mmol/L at 10 degree C and 0.34 mmol/L at 25 degree C in air. A difference between arterial and venous O sub(2) content was maintained throughout emersion, with no indication of anaerobiosis even after 24 h in air. The hypercapnia was temperature-dependent but stabilised, so that while haemolymph PCO sub(2) was approximately 2 mmHg in water and less than 3 mmHg at 10 degree C in air, it reached 7.3 mmHg at 25 degree C in air (where 1 mmHg = 0.133 kPa). Acute haemolymph acidosis occurred at both temperatures, followed by a compensatory metabolic alkalosis within 4 h. In 10 degree C air, haemolymph pH stabilised at greater than 7.9 (compared with 7.83 in water). In air at 25 degree C, the haemolymph stabilised at a relatively acidotic pH, as predicted by the 15 degree C difference in temperature. Large changes in strong ion difference were evident during emersion, but their magnitude depended on air temperature. Sustained O sub(2) transport and respiration in emersed Hemigrapsus was facilitated by the lung and not the gills since the arterial O sub(2) content (0.26 mmol/L) was lower than that of pulmonary blood (0.30 mmol/L). There was no indication of enhanced carbonic anhydrase activity in the lung to facilitate CO sub(2) excretion. Oxygen uptake was similarly limited in air as in water. An increase in cardiac output in air, exacerbated by increased temperature, suggested that Hemigrapsus may be near the limit of its aerobic scope during emersion. Increased circulating urate levels during prolonged air breathing at 25 degree C (but not 10 degree C) also indicated that O sub(2) delivery to the tissues may be limiting during emersion on warm days. Hemigrapsus nudus exercised in air for 15 min at 25 degree C required significant anaerobiosis. Field data, at temperatures intermediate between those of the laboratory studies, supported the conclusions from the laboratory data. While the scope for activity for Hemigrapsus in air may be limited, it is clear that this species is an adept air breather and that fo |
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| ISSN: | 0031-935X 1937-4267 |