Stable isotopic compositions of hydrothermal vent organisms

Stable isotopic analyses were used to study trophic relationships in two communities of deep-sea hydrothermal vent organism in the Pacific Ocean. The community at Hanging Gardens on the East Pacific Rise (21°N), sampled in 1985, is dominated by two species of vestimentiferan tubeworms; communities at Alice Springs and Snail Pits on the Marianas Back Arc Spreading Center (western Pacific), sampled in 1987, are dominated by gastropod mollusks, barnacles, and anemones. In both locations, carbon and nitrogen isotopic values of vent invertebrates are significantly different from those of non-vent invertebrates collected at 11°N on the East Pacific Rise and elsewhere in the deep-sea. These distinct isotopic compositions reflect local sources of organic carbon and nitrogen used by vent consumers. Many vent invertebrates lacking chemoautotrophic endosymbionts have ¹³C-enriched values of-11 to-16%. compared to values of-17 to-22%. normally observed in deep-sea fauna. This suggests that a ¹³C-enriched food source is trophically important in both vent communities. Free-living bacteria colonizing surfaces and suspended in the water column may constitute this food resource. Nitrogen isotopic analyses show that the food web of the East Pacific Rise community has more trophic levels than the Marianas vent community.