Air Breathing by the Purple Shore Crab,Hemigrapsus nudus(Dana). I. Morphology, Behaviour, and Respiratory Gas Exchange

Abstract

The morphometrics of the respiratory system, voluntary emersion behaviour, and gas exchange during immersion and emersion were examined in the amphibious, intertidal crab Hemigrapsus nudus. The area of the gills $(area = 993.8(body mass)^{0.83}$, where area is in square millimeters and body mass is in grams) is considerably reduced compared with that of aquatic species but similar to the gill areas of other amphibious crabs. The lungs occupy a large proportion of the branchiostegites and are highly vascularised, although the organisation of the vasculature is relatively unsophisticated compared with that of terrestrial species. Crabs voluntarily and regularly left the water, both in the field and in the laboratory, for short periods of 1-10 min, but also for extended periods of 8 h, and spent more time emersed than immersed. Oxygen consumption (∼3.4 μmol h⁻¹ g⁻¹) and the respiratory exchange ratio were essentially unchanged by the voluntary cycle of emersion and immersion. Voluntary emersion was preceded ...