NUTRITIONAL INTERACTIONS IN GALAPAGOS RIFT HYDROTHERMAL VENT COMMUNITIES - INFERENCES FROM STABLE CARBON AND NITROGEN ISOTOPE ANALYSES

Nutritional interactions among invertebrates at 3 vent sites on the Galapagos Rift are examined through the use of stable carbon and nitrogen isotopes. A large number of individuals of several vent species were analyzed and this provides previously unavailable insights into the variability within various groups. Stable nitrogen isotope contents (delta(15)N values) of vent invertebrates are below 11 parts per thousand. This is significantly lower than all non-vent deep-sea fauna examined to date, which makes delta(15)N values an excellent tool in identifying vent-dependent fauna. However, the large range in delta(15)N 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 (delta(13)C values) in vent invertebrates from the Galapagos Rift range from -9 to -37 parts per thousand, which encompasses the range of non-vent deep-sea fauna (-17 to -22 parts per thousand) and extends significantly beyond it. Many vent invertebrates have delta(13)C 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.