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The rate of incorporation of organic carbon by Daphnia p&x from various concentrations of ‘“C-labeled phytoplankton and artificial detritus was measured both in situ in West Blue Lake, Manitoba, and in the laboratory. Incorporation of artificial detritus was independent of dissolved oxygen concentration, down to a level of 2,.8 mg OS/liter, during a 4-hr experiment. Food concentration and tcmpcraturc were related, for each food type, to incorporation in multiple regression equations. Three estimates, ranging from 2.37 to 5.35 ,ug C individual-’ day”, were made of daily incorporation, assuming it was similar in natural and artificial detritus. Of these amounts, from 12 to 17% was estimated to be incorporated by Daphnia below 12 m, in the zone where particulate organic matter was predominantly detritus or moribund organisms. Variations in incorporation rate were caused primarily by temperature differences encountered during vertical migration rather than by food concentration. &cause vertical migration patterns varied, temperature regimes also varied, and so, conscqucntly, did incorporation rates. The estimated contribution of detrital carbon to total daily incorporation was much less than the phytoplankton contribution but was significant

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