Nutritional interactions in Galapagos Rift hydrothermal vent communities: inferences from stable carbon and nitrogen isotope analyses

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Nutritional interactions among invertebrates at 3 vent sltes on the Galapagos R~ft are examined through the use of stable carbon and nitrogen Isotopes. A large number of indviduals of several vent species were analyzed and this provides previously unavailable ins~ghts into the vanability within various groups. Stable nitrogen isotope contents [6I5N values) of vent ~nvertebrates are below 11 %. This is significantly lower than all non-vent deep-sea fauna examined to date, which makes 6ISN values an excellent tool in identifying vent-dependent fauna. However, the large range in 6I5N values among both primary producers and many vent consumer species renders it of limited use in determining either the trophic level of most individual species or the total number of trophic levels in vent communities. Stable carbon isotope content (6I3C values) in vent invertebrates from the Galapagos Rift range from -9 to -37x0, which encompasses the range of non-vent deep-sea fauna (-17 to -22%0) and extends significantly beyond it. Many vent invertebrates have 6I3C values which overlap that of ambient deep-sea fauna, however in several cases the extreme values can be linked to specific endogenous vent sources. When both nitrogen and carbon are taken together, robust trophic links can be established between several vent taxa, and considerable nutritional plasticity in other taxa becomes evident.