Significance of bacterial biomass in the nutrition of a freshwater isopod (Lirceus sp.)

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Abstract
The quantitative significance of bacterial biomass in the nutrition of detritivores remains equivocal. We have used tritiated thymidine to specifically label stable macromolecules in natural assemblages of sediment-associated and detritus-associated bacteria. This material was presented to the isopod (Lirceus sp.) and incorporation of bacterial biomass measured. The isopod incorporated roughly 1 ng bacterial carbon (mg wet wt.)-1 h-1 from leaf discs and about 6 ng mg-1 h-1 from sediment. Calculation of grazing rate from changes in cell counts yields grazing rates from 2.3–17.9 ng C mg-1 h-1. Even the maximum grazing rate, which is an overestimate of C assimilated, represents only 14.7% of C respired by the isopod.