title: Variability of higher trophic level stable isotope data in space and time--a case study in a marine ecosystem.
abstract: BACKGROUND
  1In shelf and coastal ecosystems, planktonic and benthic trophic pathways differ in their carbon stable isotope ratios (δ(13)C values) and nitrogen stable isotope ratios (δ(15)N values) and they increase predictably with trophic level. Stable isotope data are therefore used as a tool to study food webs in shelf and coastal ecosystems, and to assess the diets and foraging behaviour of predators. However, spatial differences and temporal changes in prevailing environmental conditions and prey abundance may lead to considerable heterogeneity in stable isotope values measured in focal animal species.
  
  
  METHODS
  Here we assess spatial and temporal variability of δ(13)C and δ(15)N values in tissue samples of fish, squid and crustacean species captured over three years during research cruises close to the Falkland Islands, Southwest Atlantic.
  
  
  RESULTS
  Both in δ(15)N values and especially in δ(13)C values, intra-species differences were large and often exceeded inter-species differences. Spatial patterns were weak, albeit statistically significant. The distribution of δ(13)C values was related to latitude, while the δ(15)N values varied with longitude. The distance from the coast and depth of catch influenced both δ(13)C and δ(15)N values. However, the importance of temporal variability greatly exceeded that of spatial variability. In addition to a moderate overall seasonal effect, we found that species differed strongly in their specific seasonal changes.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Justus Liebig University Giessen, Department of Animal Ecology & Systematics, Heinrich-Buff-Ring, 35392, Giessen, Germany.
authors.forename: Petra
authors.initials: P
authors.lastname: Quillfeldt
authors.affiliation: Justus Liebig University Giessen, Department of Animal Ecology & Systematics, Heinrich-Buff-Ring, 35392, Giessen, Germany.
authors.forename: Klemens
authors.initials: K
authors.lastname: Ekschmitt
authors.affiliation: South Atlantic Environmental Research Institute, PO Box 609, Stanley, Falkland Islands, FIQQ 1ZZ.|Directorate of Natural Resources, Fisheries Department, Stanley, Falkland Islands, FIQQ 1ZZ.
authors.forename: Paul
authors.initials: P
authors.lastname: Brickle
authors.affiliation: Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, Glasgow, G75 0QF, UK.
authors.forename: Rona A R
authors.initials: RA
authors.lastname: McGill
authors.affiliation: Justus Liebig University Giessen, Department of Animal Ecology & Systematics, Heinrich-Buff-Ring, 35392, Giessen, Germany.
authors.forename: Volkmar
authors.initials: V
authors.lastname: Wolters
authors.affiliation: Max Planck Institute for Ornithology, Department of Migration and Immuno-Ecology, Am Obstberg 1, 78315, Radolfzell, Germany.|University of Konstanz, Department of Biology, 78457, Konstanz, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Dehnhard
authors.affiliation: Justus Liebig University Giessen, Department of Animal Ecology & Systematics, Heinrich-Buff-Ring, 35392, Giessen, Germany.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Masello
mesh_terms: D000818:Animals; D059001:Aquatic Organisms / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D002247:Carbon Isotopes / Q000032:analysis*; D003445:Crustacea / Q000502:physiology; D049832:Decapodiformes / Q000502:physiology; D005399:Fishes / Q000502:physiology; D020387:Food Chain; D013058:Mass Spectrometry; D009587:Nitrogen Isotopes / Q000032:analysis*; D062211:Spatio-Temporal Analysis
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes