Metabolic status and respiratory physiology of Gecarcoidea natalis, the Christmas Island red crab, during the annual breeding migration

With the arrival of the monsoonal rains and after months of inactivity duri ng the dry season, the terrestrial crab Gecarcoidea natalis embarks on its annual breeding migration to the coast. The physiological demands of the mi gration were assessed by determining respiratory gases in the hemolymph, ke y metabolites, and energy stores in G. natalis during two migratory seasons . At the end of each day of migration the pulmonary hemolymph Po, decreased by 1-2.5 kPa, but the hemocyanin remained saturated with O-2 and the venou s reserve was largely unchanged (O-2 > 0.4 mmol . 1(-1)). The breeding migr ation of red crabs was accomplished without recourse to anaerobiosis, even though at times walking speeds (up to 6.2 +/- 0.5 m . min(-1)) exceeded tho se that promoted anaerobiosis in non-migrating crabs and in crabs exercised in the laboratory. In contrast to all previous studies, at the end of each day of migrating, red crabs experienced an alkalosis (up to 0.1 pH units) rather than any acidosis. This alkalosis was removed overnight when the cra bs were inactive. Although there were seasonal fluctuations in the glycogen, glucose, and tri glyceride stores, crabs engaging in the migration did not draw on these sto res and must have fed along the way. In contrast, crabs returning from bree ding activities on the shore terraces had significantly depleted glycogen s tores. Additionally, in 1993, the male crabs returning from the breeding ac tivities on the terraces were dehydrated and experienced a decrease in musc le tissue water of 11%. In contrast to the breeding migration per se, fight ing for burrows in which breeding occurs produced severe anaerobiosis in ma les, especially the victors: after 135 s of combat, the maximum L-lactate c oncentration in the hemolymph was 35 mmol . I-1. It appears that burrowing, courtship, and mating are more demanding than the migration itself. Furthe rmore, the data provide evidence that the metabolic responses of migrating individuals of G. natalis might be different from those at other times of t he year.