Formula omitted] values of lipids from phototrophic zone microplankton and bathypelagic shrimps at the Azores sector of the Mid-Atlantic Ridge

Abstract

The lipid composition and δ 13 C values of phototrophic zone microplankton, and species of bathypelagic shrimp that are not associated with hydrothermal vents, were determined for samples collected from the water column above the Mid-Atlantic Ridge. These analyses were compared with similar previously published data for vent bresiliid shrimp to address the hypothesis that deep-sea hydrothermal vent ecosystems are reliant on specific dietary nutrients produced by photosynthetic organisms. Microplankton (<200 μm) sampled from the surface layer (∼4 m deep) and from the region of maximum light scattering (LSM, 48–75 m deep) were analysed to determine δ 13 C values of individual fatty acids in particulate matter. The distributions of fatty acids in total lipid from the surface layer and from the LSM were very similar, with high levels (∼45% of the total) of saturated fatty acids, particularly 14 : 0, 16 : 0 and 18 : 0, and moderate amounts (∼31% of the total) of polyunsaturated fatty acids (PUFA), dominated by 22 : 6(n-3). δ 13 C values of fatty acids from the surface layer and LSM were also very similar (mean values of −27.6 and −28.8‰, respectively), with a range of values from −25.0 to −32.2‰ and PUFA being somewhat depleted in 13 C relative to saturated and monounsaturated fatty acids. Total lipid of abdominal muscle from three species of bathypelagic decapod shrimp, Ephyrina bidentata, Parapasiphaea sulcatifrons and Sergia japonicus collected from 2000 m contained 18 : 1(n-9), 16 : 0, 22 : 6(n-3) and 20 : 5(n-3) as major fatty acids in all cases. The fatty acids in total lipid from the wax ester-rich hepatopancreas of all three shrimps were dominated (∼50% of the total) by 18 : 1(n-9) and contained substantially lower levels of PUFA than muscle lipid. Total lipids from the hepatopancreas of E. bidentata and S. japonicus contained high levels of 22 : 1 alcohols and 16 : 0 alcohol, respectively, whereas total hepatopancreatic lipid from P. sulcatifrons contained mainly 18 : 1 alcohols and 16 : 0 alcohol. δ 13 C values for the fatty acids in the three species ranged from −22.4 to −30.7‰ for muscle (mean value −25.7‰) and from −23.9 to −31.9‰ for hepatopancreas (mean value −26.1‰), with PUFA again being depleted in 13 C relative to saturated and monounsaturated fatty acids. δ 13 C values for the fatty alcohols in the three species ranged from −25.7 to −29.5‰ (mean value −27.1‰). These lipid analytical and δ 13 C data are consistent with PUFAs in bathypelagic shrimps originating unmodified from PUFAs in the photic zone and wax esters in bathypelagic shrimps originating substantially from animal biosynthetic activity.