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Journal of Experimental Biology 79,265-281 (1979)
Published by Company of Biologists 1979

Respiration and Adaptation to the Terrestrial Habitat in the Land Hermit Crab Coenobita Clypeatus

BRIAN R. McMAHON ¹ and WARREN W. BURGGREN ²

¹ Department of Biology, University of Calgary, Calgary T2N 1N4, Alberta, Canada
² Zoology Department, University of Massachusetts, Amherts Ma 01003, U.S.A.

The frequencies of heart (f_H) and scaphognathite (ventilatory = f_BC) pumping, and responses to hypoxia, hypercapnia and wetting (simulated rain), as well as oxygen consumption (M_OO2), pre- and postbranchial haemolymph oxygen tension (P_OO2), oxygen content (C_OO2), carbon dioxide content (C_COCO2) and pH were measured in adult land crabs Coenobita clypeatus. There was a large increase in f_8C in response to both hypoxia and wetting but a smaller increase in response to even severe hypercapnia. Some evidence suggests that ventilation via the scaphognathites may have been supplemented by a second (branchiostegal) pump when ventilatory requirement was high. f_H was less responsive to either hypoxia or hypercapnia, but decreased with severe exposure to either. Haemolymph oxygen tensions were low (P_,O,O2 = 14, P_vOvO2 = 8) but haemocyanin oxygen affinity was high in vivo (P₅₀ = 10 torr at 23°C) and postbranchial haemocyanin was 60-80% saturated. Oxygen content was also high allowing adequate oxygen release to the tissues despite the low oxygen tensions. P₅₀/t = 0.37 torr/ °C, log P₅₀/pH = - 0.84 torr/pH unit, both determined in vitro were lower than literature values for marine and littoral species. As in other terrestrial species, C_COCO2 and P_COCO2, (calculated) were high, as were both bicarbonate and non-bicarbonate buffering capacities. Water loss was less (0-08% body weight. h^-1) in Coenobita than in other terrestrial crustaceans, this resulting from the protection of the adopted shell. Results obtained from Coenobita are compared with those from other terrestrial and littoral crabs to illustrate the influence of the adopted shell on the degree of modification needed to enter terrestrial habitats.