Tuesday, June 5, 2007 - 8:45 AM
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Do autochthonous food resources dominate mid-order Arctic stream food webs?

Angela R. Allen1, Bruce J. Peterson2, William B. Bowden3, Alex D. Huryn4, Michael B. Flinn3, Julia R. Larouche3, Kumi L. Rattenbury5, and Diane Sanzone5. (1) Brown University and the Marine Biological Laboratory, Providence, RI 02912, (2) Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543, (3) Rubenstein School of Natural Resources, University of Vermont, Burlington, VT 05405, (4) Biological Sciences, University of Alabama, 2620 University Blvd, Tuscaloosa, AL 35401, (5) National Park Service, 201 First Avenue, Fairbanks, AK 99701

The River Continuum Concept predicts that autochthonous food resources have higher relative importance in mid-order streams with reduced riparian cover. To examine this prediction in an Arctic landscape, we sampled 15 tributaries of the upper Noatak River, Alaska.  We examined stable isotope ratios of C and N in macroinvertebrate consumers and their food resources to determine the importance of autochthonous and allochthonous organic matter to the macroinvertebrates in each stream. Autochthonous sources were unusually variable in isotopic composition across sites (-10 to 14‰ δ15N, -40 to -30‰ δ13C) and much more variable than allochthonous sources (-5 to 1‰ δ15N, -29 to -26‰ δ13C). We calculated consumer resource use as binary mixtures of autochthonous and allochthonous end member sources, and determined that on average 68% of stream secondary production was supported by autochthonous carbon. Variable isotopic compositions of consumers relative to source end-members suggested that some macroinvertebrates used different feeding strategies among sites. We interpret this as a consequence of adaptable feeding behavior due to limited food resources in Arctic streams. Our results show that autochthonous food resources play a larger role than allochthonous sources in supporting consumers in these Arctic streams and this is consistent with the River Continuum Concept.