Sourcing fatty acids to juvenile polar cod (Boreogadus saida) in the Beaufort Sea using compound-specific stable carbon isotope analyses

Juvenile polar cod (Boreogadus saida) are often found in close association with sea ice and represent an important trophic link in the Arctic food web. However, the proportional contribution of sea ice algal production via the sympagic food web to the diet of polar cod is unknown. To estimate the proportional contribution of fatty acids (FAs) from sea ice-derived particulate organic matter (i-POM) to the diet of juvenile polar cod, we used FA profiling and compound-specific stable carbon isotope analysis of individual FAs from juvenile polar cod collected from three regions in the Beaufort Sea. The δ13C values of the FAs 14:0, 16:4n-1, 18:0, 20:5n-3 and 22:6n-3 in the polar cod were found to most strongly resemble pelagic POM rather than i-POM. Results from isotope-mixing models using diatom FA markers indicated that the proportional contribution of FAs from i-POM to juvenile polar cod was ≤2 %, which suggests that juvenile polar cod had not sourced their FAs from i-POM. Thus, changes in sea ice coverage due to environmental change may not affect juvenile polar cod in regard to nutrients such as FAs but may still affect their populations by reducing critical shelter from predators.