MEPS 208:265-271 (2000)  -  doi:10.3354/meps208265

Low δ13C signatures in pelagic seabirds: lipid ingestion as a potential source of 13C-depleted carbon in the Procellariiformes

D. R. Thompson1,*, R. A. Phillips2,**, F. M. Stewart3,***, S. Waldron4

1Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
2Wildfowl and Wetlands Trust, Caerlaverock, Dumfriesshire DG1 4RS, Scotland, UK
3School of Environmental and Marine Sciences, University of Auckland, Tamaki Campus, Private Bag 92019, Auckland, New Zealand
4Scottish Universities Environmental Research Centre, Scottish Technology Park, East Kilbride, Glasgow G75 0QF, Scotland, UK
Present addresses:*National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Greta Point, PO Box 14-901, Kilbirnie, Wellington, New Zealand. E-mail: **British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK ***The Glasgow Academy, Colebrooke Street, Glasgow G12 8HE, Scotland, UK

ABSTRACT: Stable-isotope ratios of carbon (δ13C) were determined in liver samples from a number of procellariiform seabirds from New Zealand. Generally, δ13C values were low (depleted in 13C) and there was a significant degree of intra- and inter-specific variation. We suggest that the pelagic versus inshore/benthic foraging model for δ13C values in marine consumers is insufficient to explain the intra- and inter-specific variation. Nor can observed δ13C values of procellariforms be linked to variation in foraging distances. We propose that carbon relatively depleted in 13C derived from dietary lipids is incorporated into proteins. Support for this hypothesis is provided by depleted δ13C signatures we measured in lipids extracted from liver tissue, which were always lower than δ13C signatures in liver tissue (by 4.2 to 6.8‰, depending on species). Additionally, δ13C values were determined in a small number of stomach-oil samples; these too were relatively depleted and lower than δ13C values measured in liver tissue. Incorporation of dietary lipids, relatively depleted in 13C, into protein could explain both intra- and inter-specific variation in δ13C signatures in procellariiforms and may represent an additional explanation for relatively low δ13C values in pelagic consumers.

KEY WORDS: Stable isotopes · Diet · New Zealand · Seabird · Foraging

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