Effect of lipid extraction on analyses of stable carbon and stable nitrogen isotopes in coastal organisms of the Aleutian archipelago

Abstract

We tested whether extracting lipids reduced confounding variation in δ13C and δ15N values by analyzing paired lipid-extracted (LE) and non-lipid-extracted (NLE) samples of bald eagle ( Haliaeetus leucocephalus (L., 1766)) whole eggs, muscle tissue from nine seabird and one terrestrial bird species, muscle tissue from four marine fish species, and blue mussels ( Mytilus edulis L., 1758) collected from the Aleutian archipelago, Alaska. Lipid extraction significantly increased δ13C by an average of 2.0‰ in whole eggs, 0.8‰ in avian muscle, 0.2‰ in fish muscle, and 0.6‰ in blue mussels. Lower δ13C values in NLE samples covaried positively with lipid content across all sample types. Lower δ13C values in NLE samples were not correlated with lipid content within bald eagle eggs and blue mussels, but covaried positively with percent lipid in avian and fish muscles. Neither lipid extraction nor percent lipid significantly changed δ15N values for any sample type. Lower δ13C values in most NLE avian and fish muscle tissues should not confound interpretation of pelagic versus nearshore sources of primary production, but lipid extraction may be necessary when highly precise estimates of δ13C are needed. Lipid extraction may not be necessary when only δ15N is of interest.