Fig. 2. (A) O₂ and H₂S and (B) CO₂ uptake rates (µmol g^-1 h^-1); (C) proton elimination rates (µequivalents g^-1 h^-1), by Riftia pachyptila as a function of seawater H₂S (µmol l^-1). The large arrow indicates that point at which H₂S was eliminated from the aquarium seawater. pH was maintained at 6.1 and all other substrates were held at `typical' concentrations (see Materials and methods). All rates are expressed in terms of wet mass.