¹³C ¹²c ratios in individual fatty acids of marine mytilids with and without bacterial symbionts

No evidence was found for isotopic fractionation at methyl carbon during methylation of fatty acids with BF₃-methanol. It is therefore possible to evaluate intermolecular carbon isotopic variations in natural fatty acids by determining the δ ¹³C composition of the corresponding methyl esters after derivatization. We illustrate the usefulness of the technique to the evaluation of dietary strategies of marine mytilids in two contrasting marine environments, a normal coastal Newfoundland estuarine system and a cold hydrocarbon seep benthic community from the Gulf of Mexico. Mussels from coastal Newfoundland have fatty acid δ ¹³C compositions of -34.4 to -24.9 0 00, whereas those from the Gulf of Mexico showed a range of -56.9 to -49.0 case:0 00. This difference is primarily ascribed to the difference in the ultimate source of Cl carbon in the two environments (CO₂ in coastal Newfoundland and CH₄ in the Gulf of Mexico). Differences observed in the nature of intermolecular carbon isotopic patterns of saturated and unsaturated fatty acids of mytilids from the two marine localities reflect the differences in the carbon pathways utilized by the organisms in their respective growth environments.