Respiratory, Acid-Base, and Metabolic Responses of the Christmas Island Blue Crab, Cardisoma hirtipes (Dana), during Simulated Environmental Conditions

The dependency of the Christmas Island blue crab, Cardisoma hirtipes, on fresh water for respiratory gas exchange and transport was investigated in laboratory simulations. The gas exchange rates of air-breathing C. hirtipes were similar to those of other land crabs but decreased to 20% in submerged...

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Bibliographic Details
Published in:	Physiological zoology 1997-01, Vol.70 (1), p.100-115
Main Authors:	Dela-Cruz, Jocelyn, Morris, Stephen
Format:	Article
Language:	eng
Subjects:	Acid-Base Equilibrium - physiology Air Animals Blood Gas Analysis Blood Glucose - metabolism Brachyura - metabolism Brachyura - physiology Breathing Calcium - physiology Carbon Dioxide - blood Carbon Dioxide - metabolism Carbon Dioxide - physiology Cardiac Output - physiology Crabs Environment Hemocyanins - metabolism Hemocyanins - physiology Hemolymph Hemolymph - chemistry Hydrogen-Ion Concentration Hypoxia Lungs Magnesium - physiology Oxygen Oxygen - blood Oxygen - metabolism Oxygen - physiology Oxygen partial pressure Respiration Respiration - physiology Respiratory gases
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Summary:	The dependency of the Christmas Island blue crab, Cardisoma hirtipes, on fresh water for respiratory gas exchange and transport was investigated in laboratory simulations. The gas exchange rates of air-breathing C. hirtipes were similar to those of other land crabs but decreased to 20% in submerged crabs. Crabs with access to air maintained arterial and pulmonary O₂ content (CO₂) and partial pressure (PO₂), while in submerged crabs the PO₂ and CO₂ rapidly decreased (by 50%). There was no anaerobiosis, but haemolymph glucose concentration and cardiac output decreased when crabs were submersed, which suggests a hypometabolic state. Submersion induced a metabolic rather than a respiratory alkalosis, and since respiratory gas exchange was low, CO₂ excretion to water was unimportant. Cardisoma hirtipes haemocyanin (Hc) has high O₂ affinity but low pH sensitivity, which facilitates O₂ uptake from hypoxic environments. The high Hc-O₂ affinity supports O₂ loading but may prevent access to a venous O₂ reserve. Calcium, magnesium, and urate, but not L-lactate, were effectors of Hc-O₂ affinity. In submerged crabs increased circulating urate maintained haemolymph O₂ content. The CO₂ capacitance and nonbicarbonate buffering of the haemolymph were relatively low. A significant Haldane effect seemed important for CO₂ excretion but would require CO₂ and O₂ exchange to occur at the same organ (gills or lungs). Submersion interferes with respiration and is not needed for haemolymph acid-base balance; thus, C. hirtipes is an air-breathing crab.
ISSN:	0031-935X 1937-4267