Tuesday, June 5, 2007 - 9:30 AM
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Effects of Three Different Carbon Sources (13C-Labeled Seston, 13C-Labeled Algal DOC, and 13C-Labeled Bacteria) on Sphaerium and Grensia in an Arctic Lake

Cassandra A. Medvedeff and Anne E. Hershey. Biology, University of North Carolina-Greensboro, 312 Eberhart Building, Greensboro, NC 27402

During summer 2006, we tested the effects of different organic matter sources on carbon assimilation by the caddisfly, Grensia, and the fingernail clam, Sphaerium, using intact sediment cores in a 1-month incubation experiment.  Organic matter sources included 13C enriched seston, 13C enriched algal DOC, 13C enriched 1-acetate, and 13C enriched 2-acetate. In the Grensia experiment, 13C enriched algal DOC and 13C enriched seston were significantly more enriched than the control.  In the Sphaerium experiment, 13C enriched seston, 13C enriched algal DOC, 13C enriched 1-acetate, and 13C enriched 2-acetate were significantly more enriched when compared to the control.  Both arctic organisms showed significant incorporation of seston only. Mixing models suggest that 65% of Grensia’s diet was derived from seston and 37% from bacteria which consumed algal DOC.  Mixing models indicated that 35% of Sphaerium’s diet is made up of seston, compared to 22% from bacteria which consumed algal DOC.  The two acetate treatments indicated that Sphaerium also fed on bacteria that had consumed acetate, and approximately half of that acetate-based diet was derived from methanogenic bacteria.  Seston and DOC derived sources are important to both diets although it appears that Grensia are more tightly linked to planktonic seston than are Sphaerium.

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