ABSTRACT
This chapter provides a protocol for estimating absorption of sediment-associated microorganisms by deposit-feeding animals. Benthic deposit feeders utilize sedimentary bacteria, microbial products, and in shallower waters, microalgae, along with detritus as part of their complex diet. The ideal radiolabeling technique would label only the target microbial group, the label would be homogeneously distributed within each cell and among different cells of the target group, and the labeled cells would not change in specific activity during the time course of the experiment. These traits are irreconcilable because metabolic activity of uniformly labeled cells will cause an efflux of the label. The best compromise is to use an intermediate labeling period, and to limit the duration of the experiment. The initial step in radiolabeling sediment is to decide on the specific activity desired for a particular experiment. This is based on the size of the smallest sample; in analyst work, it is an individual fecal pellet.
