Meeting Abstract
The ecology and productivity of the Northern Humboldt Current System is affected by interannual temperature fluctuations caused by the El Niño-Southern Oscillation (ENSO). The availability of Peruvian anchoveta (Engraulis ringens) is closely related to ENSO conditions, oscillating between warm, less productive El Niño and cool, more productive La Niña years. These conditions have the potential to induce a bottom-up effect on predators such as the Guanay cormorant (Phalacrocorax bougainvillii) and Peruvian booby (Sula variegata), whose diets consist of >80% anchoveta. We used carbon (δvC) and nitrogen (δvN) stable isotope analysis of whole blood to investigate the isotopic foraging niches of boobies and cormorants across ENSO fluctuations. We found significant differences in δ13C and δ15N values between species independent of ENSO conditions, indicating consistent foraging niche partitioning. The stable isotope values of both seabirds exhibited a parallel response to ENSO, with higher δ13C and δ15N values in both species in La Niña conditions relative to El Niño conditions. Several non-exclusive mechanisms could have led to higher blood isotope values during La Niña conditions. Upwelling and increased primary production can result in higher stable isotope values of primary producers at the base of the food web, which influences δ13C and δ15N values at higher trophic levels. Alternatively, both birds may be shifting their diet to higher trophic level prey, and/or that food chains may be elongated, during productive La Niña years. Planned analysis of stable isotope values as well as stable isotope values and stress hormones in P. bougainvillii and S. variegata feathers will help to resolve these mechanisms as well as help to assess the physiological implications of foraging under varying ENSO conditions.
