Fig. 3. Effects of decreased environmental sulfide on metabolite uptake rates (A,B) (µmol g^-1 h^-1) and proton elimination rates (C) (µequiv g^-1 h^-1) by Riftia pachyptila. Worms were kept at in situ conditions (see Materials and methods) in the aquaria until autotrophy. Gaseous hydrogen sulfide flow into the equilibration column was turned off, and the aquarium seawater sulfide concentrations dropped to levels below our limits of detection (approximately 5 µmol l^-1; Childress et al., 1984). The arrow indicates the time at which gaseous sulfide flow was stopped in the equilibration column. Rates are expressed in terms of wet mass. H₂S, total sulfide.