Long-chain polyunsaturated fatty acids (PUFAs) are essential nutrients for all marine animals that have previously been studied. Most marine animals obtain long-chain PUFAs from their diets (i.e. as products of photosynthetic processes) and few are known to be able to produce these compounds de novo. Deep-sea vent organisms live in an environment that is relatively isolated from photosynthetic sources of PUFAs, yet some species are known to contain substantial amounts of these compounds. To further understand the origins of PUFAs in deep-sea vent animals, we studied 2 annelid species; a vestimentiferan tubeworm (class Pogonophora) with endosymbiotic bacteria, and a tubicolous serpulid polychaete that feeds heterotrophically. The vestimentiferan tubeworms Ridgeia piscesae from the Juan de Fuca Ridge are rich in the monounsaturated fatty acids 16:1n-7 and 18:1n-7, the polyunsaturated fatty acids (PUFAs) 20:5n-3 and 20:4n-6, and the non-methyleneinterrupted PUFAs 20:2∆5, 13. They also contain small but significant amounts of the PUFAs 18:2n-6, 18:3n-3 and 22:6n-3. δ 13 C values of ca -14 ‰ for 16:1n-7 and 18:1n-7 suggest that these fatty acids are synthesised by chemosynthetic processes at the vent site. A δ 13 C value of -22 ‰ for 20:5n-3 in R. piscesae makes it impossible to conclusively attribute the origin of this fatty acid to either the photic zone or hydrothermal vents. The lipids of the serpulid polychaete Protis hydrothermica from the East Pacific Rise are also rich in 16:1n-7 and contain the unusual PUFAs 18:3n-7. They also contain significant amounts of 20:1n-13 and the PUFAs 20:3n-9, 20:5n-3 and 22:6n-3. Other than 22:6n-3, which had a δ 13 C of -22 ‰, the fatty acids in P. hydrothermica had δ 13 C values ranging from -33 ‰ to -41 ‰. This is consistent with the fatty acids of P. hydrothermica, other than 22:6n-3 but including 20:5n-3, originating from a chemoautotrophic carbon source in the hydrothermal vent. It cannot be excluded that the 22:6n-3 in P. hydrothermica originates in the photic zone. Potential origins of the long-chain PUFAs in hydrothermal vent animals, whether produced by photo-or chemotrophic processes or by pro-or eukaryotic organisms, are considered.
KEY WORDS: Hydrothermal vent worms · Nutrition · PUFAs · Stable carbon isotopeResale or republication not permitted without written consent of the publisher
Abstract. This study examines the composition and partitioning of lipids in the alvinocarid shrimp Rimicaris exoculata from Mid‐Atlantic hydrothermal vents. Juveniles and adults at different stages of reproductive development were dissected into abdomen, branchial and ovary/hepatopancreas tissues. Each of these tissues was analysed for total lipid and lipid class composition, and fatty acids and fatty alcohols were identified using GC and GC‐MS. Adult and juvenile shrimp differ in the partitioning of lipids between tissues. Juveniles store lipids in the abdomen as wax ester droplets and may use phosphatidyl choline as an additional reserve. Adult shrimp use triglycerides as an energy store, and triglycerides and polar lipids accumulate in ovary and hepatopancreas tissue during reproductive development. The wax ester storage droplets of juvenile shrimp contain high concentrations of n‐3 fatty acids, which are photosynthetically‐derived and thought to be important for reproductive development in crustaceans. These n‐3 fatty acids are concentrated in the ovary and hepatopancreas of adults compared to other tissues. The n‐3 fatty acid content of these adult tissues is well within that estimated for whole juvenile shrimp, supporting the hypothesis that the n‐3 fatty acids putatively required for adult reproduction are stored from the juvenile stage.
Specimens of the chemoautotrophic symbiont-bearing hydrothermal vent clam Calyptogena pacifica were collected from hydrothermal vents at the Endeavour segment of the Juan de Fuca Ridge. Total lipid was extracted from gill, foot and mantle tissues, and lipid class and fatty acid composition determined by thin layer chromatography with flame ionization detection (TLC–FID), gas chromatography (GC) and gas chromatography with mass spectrometry (GC–MS). An abundance of n–7 monounsaturated fatty acids (MUFA), especially in the gill, reflected the large contribution of chemoautotrophic symbiotic bacteria to the nutrition of this clam. The absence of n–8 MUFA suggests that C. pacifica does not contain methanotrophic symbiotic bacteria. Low levels of highly unsaturated fatty acids (HUFA) such as 20:5 n–3 and 22:6 n–3 were detected in C. pacifica and their presence is attributed to a source other than chemoautotrophic symbiotic bacteria. Significant levels of non-methylene interrupted dienoic fatty acids and eicosatrienoic acid (20:3) were also detected in C. pacifica and it is suggested that these fatty acids are synthesized from n–7 MUFA as alternatives to HUFA. In contrast to shallow water bivalves, elevated levels of triglyceride were detected in the gills compared to the mantle.
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