Fatty acid characteristics in two symbiotic gastropods from a deep hydrothermal vent of the West Pacific

TWO deep-sea gastropods, Ifremeria nautilei and Alr~iniconcha hessleri, collected on a hydrothern~al site of the North Fiji Basin (Southwestern Pacific) were analysed for polar and neutral lipids using gas-liquid chromatography/mass spectrometry. A high level of monounsaturated fatty acids (MUFAs) and a low level of 0 3 series polyunsaturated fatty aclds (PUFAs) indicated that nutrition of both gastropods was related to a food web based malnly on bacterial supply. From differences In MUFA distribution between the 2 gastropods, it appeared that most of the energy requirements of A hessleri were supplied by sulfur-oxidizing endobacteria whereas 1. nautllei probably had a mixotroph~c diet based on endogenous as well as exogenous bacteria. Given the relat~vcly high level of linoleic acid, which represented from 2 to 8"b of the phospholipid fatty acids, hydrothermal gastropods did not appear to be depleted in m6 PUFAs. It was hypothesized that they obtain linoleic acid from a pathway different to that in heterotrophic marine molluscs. In contrast to 0 6 PUFAs, both hydrothermal gastropods appeared to b e depleted in 0 3 PUFAs, indicating the limited importance of photosynthesisbased food supplies. Some non-methylene-interrupted dienes, particularly 20:209,15 which represented from 9 to 18% of the phospholipid fatty acids, may be synthesized by deep-sea symbiotic molluscs in order to restore the depleted w3 PUFAs considered a s essential for animals. Gills of both gastropods had high levels of neutral lipids, mainly MUFAs that may have originated from degradation of endobacterial phospholipids.