Functional characteristics of the blood of the deep-sea hydrothermal vent brachyuran crab [Bythograea thermydron]

Hemocyanin in the whole blood of the hydrothermal vent brachyuran crab, Bythograea thermydron, has a moderate oxygen affinity (P$_{50}$ = 6.6 millimeters of mercury at 2.6°C; pH 7.5), which unlike that of other hemocyanins is independent of temperature over the range 2° to 30°C; carbon dioxide and pH have independent effects on the oxygen affinity of this pigment. The pH effect on affinity is moderate (Δ log P$_{50}$/ΔpH = -0.34), whereas increased carbon dioxide, which can act both directly and by changing pH, has a much larger effect (Δ log P$_{50}$/ΔpH = -0.81). This blood has a moderately high degree of cooperativity (Hill cooperativity coefficient, n, was 2.8) and a large oxygen-carrying capacity for a crustacean (4.5 milliliters of oxygen per 100 milliliters of blood). These properties characterize an oxygen transport system whose function appears to be largely independent of the wide range of environmental conditions encountered around the vents.