Scripps Institution of Oceanography

Methane seeps host a diversity of metazoans that co-occur with chemoautotrophic Bacteria and Archaea, providing a model system to study trophic microbe-metazoan interactions. The goal of this dissertation is to characterize and quantify the types of microbial production consumed by methane-seep fauna. Through combined laboratory and field studies from four methane seep locations (11 New Zealand sites; Eel River; Hydrate Ridge; and Costa Rica’s Mound 12), I found that aerobic methane-oxidizing bacteria and the syntrophic partnership which mediates the anaerobic oxidation of methane are consumed within metazoan food webs. In New Zealand, two communities were largely fueled by methane: (1) a sponge which provided a habitat and trophic conduit of methane-derived production to a diversity of fauna and (2) ampharetid polychaete beds. These ampharetid beds formed a distinct community which was fueled by aerobic methane-oxidizing bacteria, as shown through stable isotopic and fatty-acid analysis coupled to a mass-specific mixing model. The Dorvilleidae, a polychaete family which excels at inhabiting areas with high microbial production, provided a ideal taxa to study metazoan trophic linkages to Archaea. In the laboratory, I raised Ophryotrocha labronica, a dorvilleid, from egg to reproduction on monocultures of archaeal, bacterial and eukaryotic food sources. This demonstrated that all domains of life can support viable metazoan populations. In contrast to current biomarker paradigms, this species exhibited isotopic enrichment (not composition) which was foodsource specific whereas fatty-acid signature was largely not; a finding that explained many of the patterns observed in the field studies. Although archaeal biomarkers were not transferred from diet to consumer, sulfate-reducing bacteria, a member of the assemblage responsible for the anaerobic oxidation of methane, provided a mechanism that identified archaeal aggregates as a food source for dorvilleids in both authigenic-carbonate and soft-sediment habitats. As a final example of microbial-metazoan interactions, during the formal description of a novel species of Yeti crab, I identified how this crab farms chemosynthetic-epibiotic bacteria by waving its bacteria-covered setae in methane-seep fluid. This research demonstrates the ubiquity of strong trophic links between chemoautotrophic microbes and heterotrophic metazoans while highlighting how these interactions vary among site and habitat at seeps.