Abstract

In order to evaluate the effect of short- and long-term hypoxia in the American horseshoe crab (Limulus polyphemus), 22 adult, healthy crabs were evaluated for this study. In group 1, baseline pH, PO₂, PCO₂, HCO₃, base excess, TCO₂ and lactate concentrations were determined from hemolymph samples collected from 10 horseshoe crabs submerged in water. Baseline results were compared to values obtained following removal from water for 5 minutes and following recovery in water for 10 and for greater than 60 min (range: 61–221 minutes). In group 2, hemolymph gas parameters were determined in 12 horseshoe crabs following shipment out of water for 24 h and compared to values obtained from group 1 animals. Following removal from water for 5 minutes, all crabs developed severe hypoxia with PO₂ levels below the detectable limit of the analyzer. No significant changes in PCO₂ concentrations were seen over time in group 1 animals. Group 2 crabs had pronounced respiratory acidosis (pH=6.7; PCO₂=46 mm Hg) following transport, and PO₂ concentrations were significantly below baseline values of group 1 animals. Baseline hemolymph gas values of the American horseshoe crab were within range reported for other aquatic vertebrates. Short-term removal of crabs from their aquatic environment causes severe hypoxia and metabolic changes. While crabs have the ability to compensate for a changing hypoxic environment if removed from water for long periods of time (24 h) severe hypercapnia and respiratory acidosis will still be present.