Marine Biology

, Volume 53, Issue 3, pp 257-262

First online:

Food-Web structure and the fractionation of Carbon isotopes in the bering sea

  • T. McConnaugheyAffiliated withInstitute of Marine Science, University of Alaska
  • , C. P. McRoyAffiliated withInstitute of Marine Science, University of Alaska

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13C undergoes modes biomagnification in the food web, apparently as a result of being respired at a slower specific rate than12C. The degree of13C enrichment at each “trophic level” is related to the fraction of assimilated carbon which is respired. Qualitative and semi-quantitative aspects of ecosystem carbon cycling can therefore be deduced from13C enrichments, provided that isotope enrichments arising from other causes are accounted for. Most important among these is lipid storage, which enriches animals in12C. This complication can be handled in various ways, here it was done by “normalizing”13C:12C ratios to a constant lipid content. Remaining variations in13C:12C ratio presumably result mainly from respiratory isotope fractionation. The Bering Sea ecosystem provided a test for this procedure. Our results illustrate certain aspects of food web structure and suggest varous functional aspects.