Stable carbon and nitrogen isotopic signatures of fauna associated with the deep-sea hydrothermal vent system of Guaymas Basin, Gulf of California

Potential food sources and the trophic position of some of the most conspicuous faunal components (vent and non-vent) were examined in the deep-hydrothermal vent system of Guaymas Basin, in the Gulf of California using carbon and nitrogen stable isotope analyses. The isotopic signatures of 13 species collected by the DSRV Alvin and Nautile mostly from sulfide-influenced habitats were analyzed. The δ13C of nine vent species had a wide range (−36.0‰ to −12.7‰), whereas the δ15N values varied from −5.0‰ to+9.4‰. The dual isotopic approach allowed the recognition of two main groups containing vent-endemic fauna. One was represented by an assemblage of eight species associated with sulfide deposits, visually dominated by the siboglinid worm Riftia pachyptila and characterized by enriched δ13C values (means −13.7‰ to −21.0‰). The second group included a single species, the bivalve Vesicomya gigas, an inhabitant of soft sediments, which had depleted δ13C and δ15N signatures (means −35.7‰ and −1.5‰). The galatheid Munidopsis alvisca is an exception among the species in the R. pachyptila aggregation, due to its depleted δ13C (−26.4‰) and an intermediate δ15N value (+5.5‰).Isotopic δ13C and δ15N signatures of four non-vent species exhibited mostly enriched δ15N values (means δ13C −27.8‰ to −13.6‰; δ15N +14.5‰ to +17.9‰), expected for higher consumers and detritivores in a deep-sea food web. They may benefit from the vent production via microbial matter or decaying vent organisms. Vent and non-vent fauna were assigned to five feeding guilds: symbiont-containing fauna, bacterivores, detritivores, predator–scavengers, and suspension-feeders. Based on isotopic values of vent and non-vent fauna, as well as that of surficial sediments, it is inferred that the hydrothermal ecosystem in the Guaymas Basin is self-supported with high-energy efficiency and with low exporting capacity to the background deep-sea food web.