Tracing carbon flow in an arctic marine food web using fatty acid-stable isotope analysis
Global warming and the loss of sea ice threaten to alter patterns of productivity in arctic marine ecosystems because of a likely decline in primary productivity by sea ice algae. Estimates of the contribution of ice algae to total primary production range widely, from just 3 to >50%, and the importance of ice algae to higher trophic levels remains unknown. To help answer this question, we investigated a novel approach to food web studies by combining the two established methods of stable isotope analysis and fatty acid (FA) analysis—we determined the C isotopic composition of individual diatom FA and traced these biomarkers in consumers. Samples were collected near Barrow, Alaska and included ice algae, pelagic phytoplankton, zooplankton, fish, seabirds, pinnipeds and cetaceans. Ice algae and pelagic phytoplankton had distinctive overall FA signatures and clear differences in δ13C for two specific diatom FA biomarkers: 16:4n-1 (−24.0 ± 2.4 and −30.7 ± 0.8‰, respectively) and 20:5n-3 (−18.3 ± 2.0 and −26.9 ± 0.7‰, respectively). Nearly all δ13C values of these two FA in consumers fell between the two stable isotopic end members. A mass balance equation indicated that FA material derived from ice algae, compared to pelagic diatoms, averaged 71% (44–107%) in consumers based on δ13C values of 16:4n-1, but only 24% (0–61%) based on 20:5n-3. Our estimates derived from 16:4n-1, which is produced only by diatoms, probably best represented the contribution of ice algae relative to pelagic diatoms. However, many types of algae produce 20:5n-3, so the lower value derived from it likely represented a more realistic estimate of the proportion of ice algae material relative to all other types of phytoplankton. These preliminary results demonstrate the potential value of compound-specific isotope analysis of marine lipids to trace C flow through marine food webs and provide a foundation for future work.
KeywordsPelagic phytoplankton Diatoms Trophic linkages Compound specific Lipid
We thank the whaling captains of Barrow and Kaktovik and the Alaska Eskimo Whaling Commission for providing samples from the whales, C. Hanns and C. George of the North Slope Borough Department of Wildlife Management for organizing and conducting bowhead sample collection, G. Sheehan of the Barrow Arctic Science Consortium for logistical assistance, fishermen at Barrow for providing arctic cod, R. Elsner at the University of Alaska Fairbanks for providing blubber samples from seals, and N. Haubenstock and T. Howe at the Alaska Stable Isotope Facility and J. Gopaul, C. Sumi and A. Timmins at Dalhousie University for technical assistance. D. Phillips and an anonymous reviewer provided comments that greatly improved the manuscript. Whale samples were collected under authorization of National Marine Fisheries Service scientific research permit 481-1464 and 782-1694. Seal specimen collections were authorized by National Marine Fisheries Service scientific research permit 782-1399. This study was funded by the Cooperative Institute for Arctic Research, the Natural Sciences and Engineering Research Council of Canada, and start up funds awarded to M. J. W. from the University of Alaska Fairbanks. Additional support was provided by Friends of Cooper Island. We declare that the study described here complies with the current laws of both the USA and Canada.
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