The Effect of a Deposit‐feeding Amphipod on the Metabolism of Benthic Microflora1

The density of a deposit‐feeding amphipod Hyalella azteca was varied experimentally in undisturbed sediment cores taken from Marion Lake, British Columbia. Epibenthic algal production, total community respiration, and bacterial oxygen consumption were measured after 48‐hr in situ incubation. As density increased community respiration also increased, in a nonlinear manner. Epibenthic algal production was stimulated within the range of natural amphipod densities, but declined at higher densities. Bacterial respiration was stimulated at amphipod densities up to four times those observed in the lake and also declined at higher densities. These data were used to compare microflora production with Hyalella’s daily calorific requirement at various densities. At natural densities, less than 10% of daily microflora production would be required to supply the energy necessary for observed rates of amphipod growth, respiration, and egg production. Fecal pellets produced by Hyalella were rapidly colonized by microorganisms. Autotrophic microorganisms increased, while respiration of heterotrophic microorganisms and solution decreased organic content of feces. Dissolved organic compounds excreted by Hyalella significantly increased the rate of recolonization of fecal material.