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Marine Ecology Progress Series

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MEPS 631:49-66 (2019)  -  DOI:

Discriminating trophic niches of carnivorous benthic macroinvertebrates with gut contents, stable isotopes, and fatty acids

Christopher A. North1,4,*, James R. Lovvorn2, Jason M. Kolts1,5, Lee W. Cooper3, Jacqueline M. Grebmeier3

1Department of Zoology and Physiology and Program in Ecology, University of Wyoming, Laramie, WY 82071, USA
2Department of Zoology and Center for Ecology, Southern Illinois University, Carbondale, IL 62901, USA
3Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, MD 20688, USA
4Present address: Department of Botany, University of Wyoming, Laramie, WY 82071, USA
5Present address: Department of Biology, Metropolitan State University of Denver, Denver, CO 80217, USA
*Corresponding author:

ABSTRACT: Predicting effects of environmental variations on species distributions requires knowledge of the trophic niches of potential competitors. We used gut contents, stable isotopes (SIs), and fatty acid (FA) biomarkers to investigate the feeding niches of 2 macrobenthic carnivore groups in the Bering Sea: the sea stars Leptasterias groenlandica and L. polaris and the whelks Neptunea heros and N. communis. Sea star guts contained no identifiable items, probably because of external digestion; gut contents were similar between whelk species. SI analyses reflect longer-term diets but require trophic discrimination factors (TDFs) between source and consumer tissues. TDFs are not available for sea stars or whelks, so we present a method for estimating TDFs. Isotopic niche diagrams differed among areas, with either inclusion of the niche of seas stars within the broader niche of whelks—about 40% overlap with similar niche breadth—or complete partitioning with a much broader niche for whelks. Analyzing FAs requires calibration coefficients (CCs) for differential assimilation into consumer tissues, but these coefficients are largely unknown for invertebrates. Moreover, cannibalism or consumption of phylogenetically related prey may confound diet estimates if FAs in carnivores are inherently more similar to those of related prey. Perhaps because of these issues, mixing models for FAs indicated different diets than indicated by SI analyses. Measurements of CCs and TDFs for a broader range of taxa are needed for applying these methods to diverse benthic consumers. Our results indicate that sea stars and whelks have diverse and overlapping diets that change with prey availability.

KEY WORDS: Calibration coefficients · Trophic discrimination factors · Echinoderm · Mollusk · Diet · Sea star · Gastropod · Whelk

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Cite this article as: North CA, Lovvorn JR, Kolts JM, Cooper LW, Grebmeier JM (2019) Discriminating trophic niches of carnivorous benthic macroinvertebrates with gut contents, stable isotopes, and fatty acids. Mar Ecol Prog Ser 631:49-66.

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