MEIOFAUNAL GRAZING OF BACTERIA AND ALGAE IN A PIEDMONT STREAM

Studies were conducted to measure the rate at which meiofauna in White Clay Creek, Pennsylvania, graze epibenthic diatoms and bacteria, and to relate consumption rates to microbial production rates or abundances. Grazing rates were obtained by two methods: 1) taxon-specific grazing was measured from the ingestion of fluorescently labeled native bacteria (FLB) and diatoms (FLD) introduced into epibenthic communities and 2) grazing by the entire meiofaunal assemblage was measured by comparing the rate of change in bacterial and diatom densities between sediment communities with ambient and reduced meiofaunal densities. Bacterial productivity was measured by [H-3]-thymidine incorporation and algal productivity by O-2 evolution. In some experiments the impact of meiofaunal grazing was assessed by calculating the generation times required by bacteria and diatoms to compensate for grazing losses. Bacterivory rates (bacteria . individual(-1). h(-1)) ranged from 6 for nematodes to 2125 for rotifers. Algivory rates (diatoms . individual(-1). h(-1)) ranged from 0 for some nematodes and rotifers to 13.5 for one rotifer taxon. Grazing measured by reducing meiofaunal density generally yielded bacterivory and algivory rates of the same order of magnitude as those obtained with the FLB and FLD technique. Meiofauna ingested only a small fraction of bacterial production except when rotifers and large ciliates were abundant. The proportion of algal productivity ingested was 0.8 and 2.5% when meiofaunal densities were low, but at high densities the calculated generation times needed for diatoms to offset grazing losses ranged from 1.3 to 5.7 d, suggesting significant grazing pressure. In the White Clay Creek epibenthos, meiofauna probably ingest little bacterial production, but they may remove a significant portion of diatom production, especially during periods of high meiofaunal density.