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 Ga lapagos Rift are examined through the use of stable carbon and nitroge n isotopes. A large number of individuals of several vent species were analyzed and this provides previously unavailable insights into the v ariability within various groups. Stable nitrogen isotope contents (de lta(15)N values) of vent invertebrates are below 11 parts per thousand . This is significantly lower than all non-vent deep-sea fauna examine d to date, which makes delta(15)N values an excellent tool in identify ing vent-dependent fauna. However, the large range in delta(15)N value s among both primary producers and many Vent consumer species renders it of Limited use in determining either the trophic level of most indi vidual species or the total number of trophic levels in vent communiti es. Stable carbon isotope content (delta(13)C values) in vent inverteb rates 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 pa rts per thousand) and extends significantly beyond it. Many vent inver tebrates have delta(13)C values which overlap that of ambient deep-sea fauna, however in several cases the extreme values can be linked to s pecific endogenous vent sources. When both nitrogen and carbon are tak en together, robust trophic links can be established between several v ent taxa, and considerable nutritional plasticity in other taxa become s evident.