Implication of fatty acids and stable isotopes to track the nutritional source of hydrothermal vent fauna in Tonga Arc, the SW Pacific

Abstract

To understand the food source of hydrothermal vent fauna, most of vent fauna with plume particles and bacterial mats were collected from an active vent field on Tonga Arc in the SW Pacific using ‘ROPOS’ ROV and analyzed for fatty acids and stable isotopes (carbon, nitrogen, and sulfur). Symbiont-bearing invertebrates (primarily Bathymodolus manusensis, Alviniconcha sp., vent shrimp Opaepele sp.) accounted for a vast majority of the biomass of the vent fauna and presumably vent crabs, Austinograea alayseae, widely distributed and most dominated top consumer fauna in this field. A high level of bacterial origin monounsaturated fatty acids (16:1ω7 and 18:1ω7) and stable isotope ratios of vent fauna and bacterial mats indicated that their nutrition mainly provides from bacteria and symbionts. Interestingly some invertebrates, shrimps and crabs, showed high levels of long-chain polyunsaturated fatty acids (20:5ω3 for vent shrimps and 22:5ω5 for vent crabs). These PUFAs could be provided from in-situ production (i.e., exogenous bacteria and fungi) rather than the sedimentation of organic matter from surface evidenced by the low photosynthetic carbon flux and stable isotope ratios. Therefore, these conjoint approaches (fatty acids and stable isotope ratios) will provide more comprehensive information on the energy flow and source in the hydrothermal vent ecosystem.