Vertebrate nutrition in a deep-sea hydrothermal vent ecosystem: Fatty acid and stable isotope evidence

The hydrothermal vent zoarcid fish Thermarces cerberus is a top predator that inhabits deep-sea hydrothermal vents on the East Pacific Rise (EPR). Bacterial chemoautotrophy at these sites supports abundant animal communities. Paradoxically, these chemoautotrophic bacteria are not known to produce polyunsaturated fatty acids (PUFA), dietary nutrients essential for all marine vertebrates. To understand how T. cerberus   successfully exploits the vent environment and obtains essential PUFA, we compared its fatty acid composition to those of its invertebrate prey. Levels of 20:5(n-3)20:5(n-3) and 22:6(n-3)22:6(n-3) in muscle and ovary tissues of T. cerberus   were low and contained higher amounts of 20:5(n-3)20:5(n-3) than 22:6(n-3)22:6(n-3). This is in contrast to most marine fish where 22:6(n-3)22:6(n-3) typically dominates. Prey items include the limpet (Lepetodrilus elevatus) and amphipods (Halice hesmonectes and Ventiella sulfuris  ) and all contained PUFA dominated by 20:5(n-3)20:5(n-3) in amounts likely to support the requirements of T. cerberus  . δC13 values of 20:5(n-3)20:5(n-3) in the invertebrate prey were consistent with synthesis from a chemoautotrophic carbon source within the vent environment. The potential origins of these PUFA are discussed in terms of the nutrition of T. cerberus and more generally in terms of the evolution of vent taxa.