Variability of higher trophic level stable isotope data in space and time - a case study in a marine ecosystem

Abstract

Seasonal differences in the relative position of species or species groups in the C-N isotope space suggest changes in the utilisation of planktonic vs. benthic trophic pathways, indicating flexible foraging strategies in response to variable environmental conditions. These seasonal differences should be taken into account when analysing higher trophic level feeding ecology with stable isotope analysis.

Is individual consistency in body mass and reproductive decisions linked to individual specialization in foraging behavior in a long‐lived seabird?

“…Annual and spatial variation in some prey species has been previously described by Quillfeldt et al. (), and this may have affected our results. Specifically, year differences in the isotopic baseline could have precluded us from finding a relationship between environmental conditions and the penguins' isotopic values.…”

“…We therefore cannot assess whether and how these isotopic values differed among years and over the broad spatial scale utilized by SRP during the prebreeding and premolt periods (Dehnhard et al 2011;Ratcliffe et al 2014). Annual and spatial variation in some prey species has been previously described by Quillfeldt et al (2015), and this may have affected our results. Specifically, year differences in the isotopic baseline could have precluded us from finding a relationship between environmental conditions and the penguins' isotopic values.…”

Analysis of stable isotope ratios in blood of tracked wandering albatrosses fails to distinguish a δ13C gradient within their winter foraging areas in the southwest Atlantic Ocean

“…However, the δ 13 C and δ 15 N values of top consumers integrate those of multiple prey (fish and squid) and may not necessarily reflect the lack of such variation at the base of the food web. Few previous studies have incorporated data on temporal variation (within and between years) in δ 13 C and δ 15 N values (but see Quillfeldt et al and the North Atlantic .…”

“…), although this is potentially an important reason for variation between top consumers of different species or populations in pelagic ecosystems of the Southern Ocean, and the North Atlantic . Several authors suggested that overall variation in stable isotope values measured in predator tissues is more likely to be related to variation in their diets and foraging distributions, but the temporal shifts and biogeographical trends in baseline isotope ratios should be considered in order to avoid misinterpretations in future studies, as suggested by Quillfeldt et al . Baseline and lower trophic level organisms may show substantial spatiotemporal isotopic heterogeneity and local enrichment in 13 C in phytoplankton during periods of elevated primary productivity will influence the isotopic values of upper trophic level organisms .…”

“…Few previous studies have incorporated data on temporal variation (within and between years) in δ 13 C and δ 15 N values (but see Quillfeldt et al [31] ), although this is potentially an important reason for variation between top consumers of different species or populations in pelagic ecosystems of the Southern Ocean, [9,32] and the North Atlantic. [33] Several authors suggested that overall variation in stable isotope values measured in predator tissues is more likely to be related to variation in their diets and foraging distributions, [34][35][36] but the temporal shifts and biogeographical trends in baseline isotope ratios should be considered in order to avoid misinterpretations in future studies, as suggested by Quillfeldt et al [31] Baseline and lower trophic level organisms may show substantial spatiotemporal isotopic heterogeneity [7,30,31] and local enrichment in 13 C in phytoplankton during periods of elevated primary productivity will influence the isotopic values of upper trophic level organisms. [37] Our results suggest that there is limited temporal variation in the δ 13 C and δ 15 N values of top consumers in our study region during the austral winter of 2009, but of course, variation in isotope ratios could be more substantial in the long term.…”