Characterizing dietary variability and trophic positions of coastal calanoid copepods: insight from stable isotopes and fatty acids |
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Authors: | Rana El-Sabaawi John F Dower Martin Kainz Asit Mazumder |
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Institution: | (1) Department of Biology, University of Victoria, PO Box 3020, Station CSC, Victoria, BC, V8W 3N5, Canada;(2) School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055, STN CSC, Victoria, BC, V8W 3P6, Canada;(3) Danube University Krems, and Interuniversity Research Center Wasser Cluster Biological Station, Dr. Carl Kupelwieser Prom-5, 32932 Lunz am See, Austria;(4) Water and Aquatic Research Program, University of Victoria, P.O. Box 3020, Station CSC, Victoria, BC, B8V 3N5, Canada;(5) Present address: Ecology and Evolutionary Biology, Cornell University, 203E Corson Hall, Ithaca, NY 14853, USA |
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Abstract: | The spring zooplankton community in the Strait of Georgia (British Columbia, Canada) is characterized by the presence of several
calanoid copepod species which collectively make up ~90% of the mezozooplankton biomass. Here, we investigate interspecific,
interannual, and geographic variability in the diets and trophic positions of these copepods using a combination of fatty
acids and stable isotopes. To characterize geographic variability in diet, we compare our findings from the Strait of Georgia
with similar data from Ocean Station P in the subarctic northeast Pacific. Both fatty acid and stable isotope signatures indicate
the existence of three trophic levels, even within the limited size range of these copepods: Neocalanus plumchrus and Calanus marshallae are primarily omnivorous, while Euchaeta elongata is carnivorous and Eucalanus bungii is herbivorous. Fatty acid markers of trophic position (e.g., DHA/EPA, 18:1n-9/18:1n-7) correlate significantly with δ15N, while markers indicating the proportion of diatoms to flagellates in the diet (e.g., 16PUFA/18PUFA and DHA/EPA) correlate
significantly with δ13C, after the effect of lipid concentration on δ13C is accounted for. Despite the general correlation between stable isotopes and fatty acids, the former are not sensitive
enough to capture the range of interannual variability observed in the latter, and can only capture substantial shifts in
the diet over geographic scales. However, regardless of variability in food quality, the relative trophic positions of these
copepods do not change significantly either spatially or temporally. |
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