The burrow microhabitat of the land crab Cardisoma guanhumi: Respiratory/ionic conditions and physiological responses of crabs to hypercapnia
Pinder, Alan W.
Smits, Allan W.
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Cardisoma guanhumi in Puerto Rico spend much of the dry season in burrows that descend to groundwater. Burrows are sometimes 3-4 m deep and may be capped with dried mud for over 3 mo. Samples of gas and water from burrows at three locations in Puerto Rico were analyzed for O-2, CO-2, and ions. Osmolality and ion composition varied widely with location, from about 10% to 130% of seawater. Both gas and water PO-2's were generally 90-120 mmHg, although some water samples were extremely hypoxic (PO-2 lt 20 mmHg). Most burrows were extremely hypercapnic, with gas and water PCO-2's up to 60 and 90 mmHg, respectively. Whether the burrow was plugged or even occupied by a crab made little difference to ion or gas concentrations. Radiotelemetry of the vertical position of crabs in their burrows indicated that they did not avoid hypercapnia and hypoxia by staying close to the entrance, Cardisoma guanhumi are thus exposed to extreme changes in PCO-2 when they descend deep in their burrows after foraging at dawn and dusk. Impedance measurements of branchial ventilation and heart rate in resting crabs exposed to environmental hypercapnia in artificial burrows revealed two distinct types of ventilatory responses based on the degree and duration of hypercapnia: hyperventilation in response to gradual, chronic exposure to elevated burrow CO-2 and apnea in response to rapid elevations of burrow CO-2 above 4%. These physiological responses suggest the presence of both "external" and "internal" receptors of hypercapnia that may allow Cardisoma to buffer large acid-base disturbances when moving between extremes in gaseous microenvironments.
Pinder, Alan W., and Allan W. Smits. 1993. "The burrow microhabitat of the land crab Cardisoma guanhumi: Respiratory/ionic conditions and physiological responses of crabs to hypercapnia." Physiological zoology 66(2): 216-236.