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Carbon and nitrogen assimilation in the Bering Sea clams Nuculana radiata and Macoma moestaWe analyzed bulk carbon and nitrogen stable isotope values (delta C-13 and delta N-15) of the benthic clams Nuculana radiata and Macoma moesta from the Bering Sea during controlled feeding experiments (spring of 2009 and 2010) using isotopically labeled sea ice algae. The aim was to determine the ability of these clam species to assimilate carbon and nitrogen from sea ice algae. Specimens were collected in the Bering Sea and placed into jars without sediment (2009, N. radiata only) or into natural sediment cores (2010, both species). The clams were offered isotopically enriched (both C and N) or non-enriched algal feeds for time periods of 42 (2009) and 18 d (2010). Isotopic assimilation rates for carbon and nitrogen were calculated using the change in the isotope ratios of the clams over the experimental time. N. radiata in the jar experiments had slow isotopic assimilation rates (0.01 to 0.23 parts per thousand d(-1)), with solvent-extractable organic matter/lipids taking up both of the isotope markers fastest and muscle tissue the slowest. Lipids may thus be particularly suitable to track the immediate ingestion of sea ice algal production in benthic consumers. M. moesta showed 30% higher isotopic assimilation compared to N. radiata in sediment cores, likely reflecting the different feeding behaviors of these two species. Based on our results, N. radiata is likely better able to utilize food sources buried in the sediment and may be more competitive over the sediment surface feeding M. moesta under conditions of reduced ice algal production in the northern Bering Sea. (C) 2012 Elsevier B.V. All rights reserved.
CARBON AND NITROGEN ASSIMILATION IN THE CLAMS NUCULANA RADIATA AND MACOMA MOESTA FROM THE BERING SEAThe predicted climate-induced reduction in sea ice presence in the Bering Sea could impact benthic trophic interactions; however, species-specific consumer dependence on ice algal production is largely unknown. My objective was to track feeding in the benthic clams, Nuculana radiata and Macoma moesta, using stable carbon and nitrogen isotopes. Nuculana radiata had slow isotopic assimilation rates, with lipids taking up isotope markers fastest and muscle tissue the slowest. Lipids may thus be particularly suitable to track the immediate ingestion of sea ice algal export in benthic consumers. When isotopically enriched food was added to natural sediment cores, N. radiata assimilated 60% less of the isotope markers than when feeding on algal food in isolation. Possibly, this difference is related to the ingestion of other, naturally present food sources in the sediment. Macoma moesta showed 30% higher isotopic assimilation compared to N. radiata in sediment cores. I suggest that differing feeding behaviors between the species provide differential access to the sedimented algal food. Based on these results, N. radiata is likely better able to utilize food sources buried in the sediment and may be more competitive over M. moesta under conditions of reduced ice algal production in the northern Bering Sea.