Temporal variation in isotopic composition of Spheniscus magellanicus at Martillo Island

Due to their restricted foraging range, flightless seabirds are ideal models to study the short-term variability in the trophic niche in response to food availability in changing environments. In order to estimate potential inter-annual variations in trophic niche of Magellanic penguins at Martillo Island (Beagle Channel, Argentina), we investigated short-term isotopic variations in δ13C and δ15N values on feathers collected during 5 seasons (2009, 2013-16) together with oceanographic conditions. We found that in 2009 both isotopic values were higher than those registered for the rest of the studied years (p<0.001) and related with positive sea surface temperature anomalies (p<0.001). Although there are other physical, chemical and biological factors that influence the isotopic composition at the base of the food web, a higher water temperature reduces CO₂ solubility, which causes less phytoplanktonic fractionation against 13C, this is reflected in higher δ13C values in primary producers, thereby, affecting the isotopic values of rest of the trophic web. High δ15N values can be explained by 1) a higher microbial activity stimulated by temperature that enriches nitrogen inputs in 15N or 2) diet based on a higher trophic level. These results are a trigger for new questions and might help understanding the relation between Magellanic penguin’s diet and environmental conditions, especially in the actual global change scenario.