Impact of deposit-feeding chironomid larvae (Chironomus riparius) on meiofauna and protozoans.

Chironomid larvae are common members of benthic systems in freshwaters. Their diet consists mainly of detritus, which often leads to the passive ingestion of attached organisms. We hypothesized that larvae would have a strong trophic effect on protozoans and meiofauna. We investigated experimentally the direct effect of 2 densities (1 and 4 larvae/16 cm²) of Chironomus riparius, a nonselective macrofaunal deposit feeder, on a natural zoobenthic community. Larvae significantly reduced the abundance of total meiofauna (nematodes, rotifers, oligochaetes, and copepods) to 56 (1 larva) and 52% (4 larvae) of their initial abundance after 1 d. Protozoans were slightly reduced by 1 larva but their densities increased when 4 larvae were present. A strong decrease in copepod abundance led to a decrease in total meiofaunal biomass to 40 (1 larva) and 43% (4 larvae) of their initial biomass after 8 d. Organisms with body lengths between 0.125 and 1 mm were ingested preferentially. These results indicate that the presence and feeding behavior of chironomids can strongly shape meiobenthic communities and indirectly affect protozoans. [ABSTRACT FROM AUTHOR]