Characterizing dietary variability and trophic positions of coastal calanoid copepods: insight from stable isotopes and
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ORIGINAL PAPER
Characterizing dietary variability and trophic positions of coastal calanoid copepods: insight from stable isotopes and fatty acids Rana El-Sabaawi Æ John F. Dower Æ Martin Kainz Æ Asit Mazumder
Received: 30 June 2008 / Accepted: 2 October 2008 / Published online: 20 December 2008 Ó Springer-Verlag 2008
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 d15N, while markers indicating the proportion of diatoms to flagellates in the diet (e.g., 16PUFA/18PUFA and DHA/ EPA) correlate significantly with d13C, after the effect of lipid concentration on d13C 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.
Communicated by U. Sommer. R. El-Sabaawi (&) J. F. Dower A. Mazumder Department of Biology, University of Victoria, PO Box 3020, Station CSC, Victoria, BC V8W 3N5, Canada e-mail: [email protected] J. F. Dower School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055, STN CSC, Victoria, BC V8W 3P6, Canada M. Kainz Danube University Krems, and Interuniversity Research Center Wasser Cluster Biological Station, Dr. Carl Kupelwieser Prom-5, 32932 Lunz am See, Austria A. Mazumder Water and Aquatic Research Program, University of Victoria, P.O. Box 3020, Station CSC, Victoria, BC B8V 3N5, Canada Present Address: R. El-Sabaawi Ecology and Evolutionary Biology, Cornell University, 203E Corson Hall, Ithaca, NY 14853, USA
Introduction Copepods, an important component of marine ecosystems, are capable of utilizing a wide range of diets (Kleppel 1993). The trophic flexibility of omnivorous organisms can act as a stabilizing force in aquatic ecosystems (Sprules and Bowerman 1988). However, omnivory also affects foodchain length, and can change the quality of food available to higher consumers (Hairston a
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