High incidence of invertebrate‐chemoautotroph symbioses in benthic communities of the New Zealand fjords

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In the New Zealand fjords, hydrogen sulfide production from decomposing forest litter is used by chemoautotrophs to fix CO2[aq] and support benthic food webs. We used quantitative surveys and stable isotope analyses to investigate the contribution of chemoautotrophy to shallow (50 m) and deep (400 m) benthic communities in Doubtful and Bradshaw Sounds. Prevalence of bivalve‐chemoautotroph symbioses varied between shallow sites where large‐bodied (≤ 50 mm) Solemya parkinsonii (Solemyidae) were common, and deep‐basin sites where small‐bodied (< 2 mm) Nucinella maoriana (Manzanellidae) dominated assemblages. δ13C and δ15N of sediment indicated that the basal carbon source supporting chemosynthesis was likely decomposing forest litter at 50 m, and decomposing marine algae at 400 m. An isotopic mass balance model weighted to community composition and biomass indicated that the majority of carbon supporting communities at 50 m originated from chemoautotrophy. Concentration of fatty acid biomarkers for heterotrophic bacteria (C15 and C17) were correlated with the estimated amount of carbon from terrestrial sources, indicating that decomposing forest litter is important in the system. Analysis of the trophic level of these macroinfaunal communities normalized to biomass indicated that the communities sampled from 50 m were on average chemoautotrophic, whereas those sampled at 400 m were on average heterotrophic. The reliance of benthic invertebrate communities on decomposing forest litter and chemoautotrophy, particularly in shallow habitats, demonstrates close connectivity between terrestrial and marine ecosystems in this region and illustrates how diverse food webs can be supported in the shaded and quiescent inner fjord environments.