Grazing of protozoa, bacteria, and diatoms by meiofauna in lotic epibenthic communities

The role of meiofauna as grazers of microorganisms in streambed sediments in White Clay Creek (Chester Co., Pennsylvania) was studied using microcosm experiments and quantification of meiofauna densities in situ. The primary objective was to determine meiofauna ingestion rates of protozoa, but in each experiment meiofauna ingestion of either bacteria or diatoms also was measured. Meiofauna densities were manipulated in microcosms and the effect on the net specific growth rate of the food resource was measured, from which clearance rates and ingestion rates were calculated. Generation times of prey groups in the absence of meiofauna grazing could also be estimated with this experimental approach. To help relate grazing rates to meiofauna densities in White Clay Creek, streambed samples were collected for meiofauna enumeration at approximately monthly intervals. Meiofauna densities ranged from 4 to 1094 animals/10 cm(2) and biomasses from <0.1 to 1.4 mg C/10 cm(2) during the study period. Bacterivory by meiofauna was undetectable. In one experiment diatoms were ingested at a rate of 541 diatoms . meiofauna(-1) . h(-1), representing the consumption of 1.6% of diatom abundance per h. In 4 out of 5 experiments protozoa were ingested at rates ranging from 46 to 153 cells . meiofauna(-1) . h(-1). At these rates meiofauna could ingest between 2.1 and 3.0% (2.6 +/- 0.3, (x) over bar +/- SD, n = 6) of protozoan abundance per h.