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MEPS

Marine Ecology Progress Series

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MEPS is a leading hybrid research journal on all aspects of marine, coastal and estuarine ecology. Priority is given to outstanding research that advances our ecological understanding.

Online: ISSN 1616-1599

Print: ISSN 0171-8630

DOI: https://doi.org/10.3354/meps

Impact Factor2.1 (JCR 2025 release)

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Volume contents
Mar Ecol Prog Ser 611:1-18 (2019)

DOI: https://doi.org/10.3354/meps12856

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Trophic position and foraging ecology of Ross, Weddell, and crabeater seals revealed by compound-specific isotope analysis

ABSTRACT:

Ross seals Ommatophoca rossii are one of the least studied marine mammals, with little known about their foraging ecology. Research to date using bulk stable isotope analysis suggests that Ross seals have a trophic position intermediate between that of Weddell Leptonychotes weddellii and crabeater Lobodon carcinophaga seals. However, consumer bulk stable isotope values not only reflect trophic dynamics, but also variations in baseline isotope values, which can be substantial. We used compound-specific isotope analysis of amino acids (CSI-AA) to separate isotopic effects of a shifting baseline versus trophic structure on the foraging ecology of these ecologically important Antarctic pinnipeds. We found that Ross seals forage in an open ocean food web, while crabeater and Weddell seals forage within similar food webs closer to shore. However, isotopic evidence suggests that crabeater seals are likely following sea ice, while Weddell seals target productive areas of the continental shelf of West Antarctica. Our CSI-AA data indicate that Ross seals have a high trophic position equivalent to that of Weddell seals, contrary to prior conclusions from nitrogen isotope results on bulk tissues. CSI-AA indicates that crabeater seals are at a trophic position lower than that of Ross and Weddell seals, consistent with a krill-dominated diet. Our results redefine the view of the trophic dynamics and foraging ecology of the Ross seal, and also highlight the importance of quantifying baseline isotope variations in foraging studies.

KEYWORDS

Ross seal Weddell seal Crabeater seal Compound-specific isotopes Amino acids Antarctica Foraging ecology Trophic dynamics
A female Weddell seal resting on ice with her pup lying next to her on her left.

Weddell seal female and her pup in McMurdo Sound, Antarctica. 

Photo: Daniel P. Costa.

Bulk stable isotope analysis has become a common tool to assess foraging ecology of pinnipeds. However, consumer bulk stable isotope values not only reflect trophic dynamics, but also variations in baseline isotope values. Brault et al. used compound specific isotope analysis of amino acids (CSI-AA) to separate isotopic effects of a shifting baseline versus trophic structure on the foraging ecology of Antarctic pinnipeds. They found that crabeater and Weddell seals forage within similar food webs closer to shore whereas Ross seals forage in a distinct open ocean food web. Additionally, their CSI-AA data indicated that Ross seals have a high trophic position equivalent to that of Weddell seals, which differs from conclusions of nitrogen isotope results on bulk tissues.

Emily K. Brault (Corresponding Author)

  • Ocean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
ebrault@ucsc.edu

Paul L. Koch (Co-author)

  • Earth and Planetary Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA

Daniel P. Costa (Co-author)

  • Ecology and Evolutionary Biology, University of California, Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95064, USA

Matthew D. McCarthy (Co-author)

  • Ocean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA

Luis A. Hückstädt (Co-author)

  • Ecology and Evolutionary Biology, University of California, Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95064, USA

Kimberly T. Goetz (Co-author)

  • National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Wellington 6021, New Zealand

Kelton W. McMahon (Co-author)

  • Graduate School of Oceanography, University of Rhode Island, 215 S Ferry Rd, Narragansett, RI 02882, USA

Michael E. Goebel (Co-author)

  • Antarctic Ecosystem Research Division, NOAA Fisheries, Southwest Fisheries Science Center, 8901 La Jolla Shores Dr., La Jolla, CA 92037, USA

Olle Karlsson (Co-author)

  • Department of Environmental Research and Monitoring, Swedish Museum of Natural History, Box 50007, 104 05 Stockholm, Sweden

Jonas Teilmann (Co-author)

  • Department of Bioscience - Marine Mammal Research, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark

Tero Härkönen (Co-author)

  • Department of Environmental Research and Monitoring, Swedish Museum of Natural History, Box 50007, 104 05 Stockholm, Sweden
  • Martimas AB, Höga 160, 442 73 Kärna, Sweden

Karin C. Harding (Co-author)

  • Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, 405 30 Gothenburg, Sweden

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