Fig. 2. Plots of proton elimination rate (µequiv g^-1 h^-1) versus (A) total sulfide uptake rate (µmol H₂S g^-1 h^-1) and (B) total sulfide concentration (µmol l^-1) by Riftia pachyptila. The regression lines for the relationship between proton elimination rate and total sulfide uptake rate (A), and the relationship between proton elimination rate and environmental total sulfide (B) are highly significant (P<0.0001 and P<0.005; ANOVA). In this experiment, the total dissolved sulfide concentration in the seawater was increased incrementally from 100 to 408 µmol l^-1, while sulfide uptake and proton elimination rates were determined simultaneously. All other conditions were held under approximately in situ conditions (CO₂=5.5 mmol l^-1, [O₂]=250 µmol l^-1, [NO₃^-]=40-65 µmol l^-1, pH 6.2; temperature, 12°C, pressure, 27.5 MPa). Rates are expressed in terms of wet mass.