Two approaches for the estimation of baseline CUE δ¹⁵N values from mussel isotopic data.

<p>The CSI-AA approach, based on average values for δ¹⁵N_Phe (filled circles, solid regression line) predicts average baseline δ¹⁵N values most consistent with expected NO₃⁻ δ¹⁵N gradients along the CA coast. An alternate approach is based on measured bulk δ¹⁵N values, adjusted for an assumed trophic position (open diamonds, dashed regression line). This approach cannot take into account either TEF or tissue-specific fractionations, and returns lower than expected values in most locations. The regression for measured bulk δ¹⁵N values in adductor muscle tissue (heavy dashed line) is provided for reference.