Carbon isotope values of individual amino acids were measured. Clam specimens were collected at USGS Sites 2.1 and processed following Stewart et al. (2013; doi:10.3354/meps10503). Amino acids were hydrolyzed from clam muscle tissue, derivatized, and isolated following Vokhshoori et al. (2013; doi:10.3354/meps10746). The measurement of the carbon isotope values of individual amino acids were conducted following Vokhshoori et al., 2013 and Vokhshoori and McCarthy, 2013 (doi:10.1371/journal.pone.0098087), respectively.