Sulphur isotopic compositions of deep-sea hydrothermal vent animals

Abstract

Dense animal assemblages consisting of vestimentiferan worms, brachyuran crabs and giant clams have been found clustered around deep-sea hydrothermal vents in unusual ecosystems that appear to be independent of photosynthetically produced nutrients. Reduced compounds such as H2S, H2 and CH4 are spewed from the vents into the cold, oxygenated bottom water1,28, and it has been suggested that chemoautotrophic bacteria are important primary producers of organic nutrients ultilized by the vent fauna2–7. In some instances, sulphur-oxidizing bacteria may perform this function through growth as symbionts8,9 within tissues of host animals (clams and vestimentiferans). To gain further insight into sulphur metabolism in these unusual food webs, we have analysed the stable sulphur isotope ratios (34S/32S) of Pacific vent fauna and find δ34S values close to 0‰. These values approximate the +1 to +4‰ range observed for sulphur-bearing minerals at the vents, and indicate that this specialized fauna utilizes sulphur derived from the vents (rather than from seawater sulphate) during growth and metabolism.