A new method to reconstruct fish diet and movement patterns from δ13C values in otolith amino acids

Fish ecologists have used geochemical values in otoliths to examine habitat use, migration, and population connectivity for decades. However, it remains difficult to determine an unambiguous dietary delta C-13 signature from bulk analysis of otolith. Studies to date have focused on the aragonite component of otoliths with less attention paid to the organic fraction. We describe the application of compound-specific stable isotope analysis (SIA) to analyze amino acid (AA) delta C-13 values from small amounts (<1 mg) of otolith powder. We examined delta C-13 values of otolith and muscle AAs from a reef-associated snapper (Lutjanus ehrenbergii (Peters, 1869)) collected along a carbon isotope gradient (isoscape) from seagrass beds to coral reefs. Carbon isotope values in otolith and muscle samples were highly correlated within and among coastal habitats. Moreover, delta C-13 values of otolith AAs provided a purely dietary record that avoided dilution from dissolved inorganic carbon. Otolith AAs served as a robust tracer of delta C-13 values at the base of the food web, making compound-specific SIA a powerful tool for dietary reconstructions and tracking the movement of fishes across isoscapes.