Trophic ecology of Rimicaris exoculata: a combined lipid abundance stable isotope approach

The alvinocaridid shrimp Rimicaris exoculata is an abundant component of th e biota of Mid-Atlantic Ridge hydrothermal vents. To determine the nutritio nal strategy of this organism, we analysed the molecular abundance and carb on isotopic composition of its phospholipid fatty acids. High abundances of n-7 fatty acids (> 40% total fatty acids) were observed in R. exoculata mu scle tissues, in bacterial epibionts scraped from its gill bailers, and fro m the bacterially infested metal sulphides that the shrimp ingest. The phos pholipid fatty acid abundance data indicates that the bacteria in the sulph ides are closely related to the bacterial epibiota inhabiting the shrimp gi ll bailers, carapace and other body parts. Compound specific delta(13)C ana lyses of the phospholipid fatty acids gave average values of -12 parts per thousand, for the epibiont bacteria and -21 parts per thousand, for the sul phide bacteria. This difference may be largely due to the expression of dif ferent forms of RuBisCO (Forms I and II) which fractionate against C-13 to different extents. Carmay be an additional factor. The delta(13)C values bo n limitation within the shrimp epibiont population (mean = -13 parts per th ousand) of the saturated and monounsaturated fatty acids isolated from the muscle tissues of R. exoculata were very close to those of the epibionts, i ndicating that the predominant source of dietary carbon for the shrimp is t heir epibionts, with a lesser contribution from free-living bacteria. The d elta(13)C values (-26 parts per thousand). Of shrimp cholesterol were much more negative than those of the fatty acids, and this cholesterol is likely to have derived from the oceanic photic zone.