Using fatty acids as dietary tracers in seabird trophic ecology: Theory, application and limitations

Analysis of fatty acids (FAs) is an increasingly utilized tool in studies of trophic ecology in marine ecosystems. This powerful technique has proved useful in delineating spatial and temporal variability in diets, identifying the consumption of key species, and providing quantitative estimates of diet composition. Although consumer FA signatures are undeniably influenced by diet, they can also be affected by other factors including life-history stage, diet quality, and physiological state. Here, we review how FAs are assimilated, deposited, and metabolized in birds, and the implications of these processes on the various tissues commonly sampled for FA analyses. We then examine the assumptions underlying FA signature analysis when used in studies of seabird trophic ecology and propose a direction for future laboratory experiments that are needed to refine the approach. The correct interpretation of FA data relies on accounting for factors that alter predator FA metabolism and controlling for variability in the lipid content and FA composition of prey. Efforts should also be made to incorporate uncertainty associated with predator metabolism into models designed for quantitative diet estimation.