Tracing energy source and flow of hydrothermal vent fauna from the KIOST Vent Field at the Indian Ocean mid-ocean ridge

Abstract

We investigated carbon fixation pathways and energy flow in benthic ecosystems in newly discovered hydrothermal vent site, named KIOST Vent Field (KVF), at the Indian Ocean mid-ocean ridge. To do this, we analyzed sulfur (δ34S), carbon (δ13C), and nitrogen (δ15N) stable isotopic compositions in surface sediments, particulate organic matter (POM) from surface chlorophyll maximum layer (water depth = ca. 90 m), and vent fauna including mollusks, arthropods, and polychaetes collected from the KVF. The δ34S values in benthic organisms ranged from 1.8‰ to 12.8‰ indicating uptake of chemosynthetically rather than photosynthetically (POM = 18.7‰) derived organic matter. The δ13C values ranged widely between -31.7‰ (mussels) and -11.5‰ (gastropod) suggesting the occurrence of different metabolic pathways of energy production (i.e. CBB cycle, rTCA cycle, and methanotrophs) in the KVF and variation in energy sources contributions to vent fauna. For example, mussels (-31.7‰) may have derived their energy largely from the CBB cycle organic matter indicated by 13C-depleted δ13C values, whereas shrimp (-15.0‰), crab (-16.5‰), and gastropods (-11.5‰) may have taken organic matter produced by rTCA cycle or methanotrophs which have relatively high δ13C values. The δ15N values indicate trophic position of the organisms and increase by 3.4‰ by trophic level. Shrimp recorded highest δ15N values (5.7‰) while gastropod