Fatty acids in neutral and polar lipids were used to investigate trophic connections in species from five families of demersal (Rajella fyllae, Malacoraja senta, Alepocephalus bairdii, Borostomias antarcticus) and pelagic fish (Bathytroctes macrolepis, Lampanyctus spp., Chaulidos sloani, Serrivomer beanii) sampled in the deep Atlantic Ocean off Newfoundland, Canada. Lipid extracts were fractionated into neutral, acetone-mobile polar, and phospholipids to separate fatty acids in storage from those in membranes. Multivariate analysis of fatty acids showed that there were greater differences among the three lipid fractions than there were among the species when all fatty acid fractions were considered together. Neutral lipid fatty acids were characterized by monoenes, acetone-mobile polar lipids (AMPL) by C18 polyenes, and phospholipids by 16:0 and DHA. Multivariate analysis of fatty acids in phospholipids showed a strong grouping by taxonomic family (>80% similarity), while the neutral lipid fatty acids showed a weaker grouping by family (72.5% similarity) but groupings that also related to habitat and vertical migration. The neutral lipid data supported the use of 20:1ω9 as a biomarker of calanoid copepods and of 16:1ω7 as a marker of diatoms to determine food web connections in deep-sea fish, but not some other common markers. In addition, correlations with δ15N showed that series of ω6 and ω7 fatty acids were trophically transferred though neutral lipids, especially the essential fatty acid, ARA. Neutral lipids were also reservoirs for essential ω3 fatty acids in demersal species, but the major reservoir for DHA was AMPL and phospholipid in pelagic species.

The lipophilic vitamin and fatty acid profiles were determined in five edible seaweeds: Corallina elongata J. Ellis & Solander, 1786; Cystoseira barbata (Stackhouse) C. Agardh, 1820; Jania rubens (Linnaeus) J.V. Lamouroux, 1816; Laurencia obtusa (Hudson) J.V. Lamouroux, 1813 and Sargassum vulgare C. Agardh, 1820. Saturated fatty acids (SFAs) were the major fatty acid group, and16:0 formed the highest SFA content (34–40%). 16:0 was higher in the brown seaweeds (C. barbata, 40.55%; S. vulgare, 37.11%) than in the red seaweeds (C. elongata, 36.5%; L. obtusa, 34.57%; J. rubens, 34.22%). The other major fatty acids in the seaweeds were 18:1n-9 and 16:1n-7 from MUFA in the analyzed species. In addition, EPA was found in significant levels in the red seaweeds, whereas DHA was not detected in the analyzed species. The findings showed that difference among species were not statistically significant (p = 0.09–0.11), yet differences between two families (Sargassaceae and Corallinaceae) were significant (p = 0.006) in the fatty acid profile (p < 0.01). Also, differences between the Corallinaceae and Rhomomelaceae families were partially significant (p = 0.011–0.013) (p < 0.01). K1 and K2 vitamins as well as δ-tocopherol, α-tocopherol and retinol acetate were determined to be present in the seaweed extracts. Finally, ergosterol, stigmasterol and ß-sitosterol were found in all samples in differing ratios per species.

Triterpenoid biosynthesis is generally anaerobic in bacteria and aerobic in Eukarya. The major class of triterpenoids in bacteria, the hopanoids, is different to that in Eukarya, the lanostanoids, and their 4,4,14-demethylated derivatives, sterols. In the deep sea, the prokaryotic contribution to primary productivity has been suggested to be higher because local environmental conditions prevent classic photosynthetic processes from occurring. Sterols have been used as trophic biomarkers because primary producers have different compositions, and they are incorporated in primary consumer tissues. In the present study, we inferred food supply to deep sea, sponges, cnidarians, mollusks, crustaceans, and echinoderms from euphotic zone production which is driven by phytoplankton eukaryotic autotrophy. Sterol composition was obtained by gas chromatography and mass spectrometry. Moreover, we compared the sterol composition of three phyla (i.e., Porifera, Cnidaria, and Echinodermata) collected between a deep and cold-water region and a shallow tropical area. We hypothesized that the sterol composition of shallow tropical benthic organisms would better reflect their photoautotrophic sources independently of the taxonomy. Shallow tropical sponges and cnidarians from environments showed plant and zooxanthellae sterols in their tissues, while their deep-sea counterparts showed phytoplankton and zooplankton sterols. In contrast, echinoids, a class of echinoderms, the most complex phylum along with hemichordates and chordates (deuterostomes), did not show significant differences in their sterol profile, suggesting that cholesterol synthesis is present in deuterostomes other than chordates.

). Average total lipid content was determined as percentage (%) and per individual (mg ind -1 ). It was proportionally highest in February (7.03%) and lowest in September (3.02%). However, average lipid content per individual was highest in February (0.11 mg ind -1 ) and lowest in September and November (0.04 mg ind -1 ). Major fatty acids in C. euxinus were identified as 16:0, 16:1 n-7, EPA and DHA. ∑SFA, ∑MUFA, ∑PUFA and ∑HUFA were observed to be correlated with temperature. ∑SFA and ∑MUFA increased with the rise in temperature (r 2 =0.74, r 2 =0.73, p<0.05, respectively) whereas ∑PUFA and ∑HUFA increased as temperature decreased (r 2 =-0.73, r 2 =-0.80, respectively, p<0.05). Additionally, while ∑PUFA and ∑HUFA increased (r 2 =0.61, r 2 =-0.68, respectively, p<0.05), ∑MUFA decreased (r 2 =-0.68, p<0.05) as chlorophyll-a increased. It was observed that the degree of unsaturation increased as temperature decreased. Results of the study revealed that C. euxinus has rich lipid content as well as fatty acid composition and it plays an important role in the South-eastern Black Sea ecosystem functionalities especially having key role in energy fluxes to higher trophic levels.