The effect of invertebrate consumption on bacterial transport in a mountain stream

Abstract

Although laboratory studies have shown that filter-feeding invertebrates consume bacteria from stream water, no study has measured bacterial consumption in the field or determined system-level removal rates of sestonic bacteria. To examine bacterial removal rates and consumption by invertebrates, we released fluorescently labeled bacteria (FLB) into a second-order stream at Coweeta Hydrologic Laboratory, North Carolina. We performed two 1-h releases during summer over bedrock habitat that supports many filter-feeders. We calculated uptake length and counted FLB in the guts of seven insect taxa. Uptake length was 78 and 83 m for the two releases, which corresponded to uptake rates of 4.03 and 3.69 x 107 cells m-2 min-1. Simulium, a filter-feeding blackfly larva, ingested FLB at a rate of 1.4 x 104 cells mg-1 min-1, 10 times the rate of other taxa. Diplectrona and Parapsyche, hydropsychid caddisfly filter-feeders, had ingestion rates between Simulium and other taxa. Epeorus, a scraping mayfly, and Tallaperla, a shredding stonefly, also ingested FLB, presumably from cells that adhered to the substrate. Invertebrate ingestion per square meter of stream bottom was 7% of total stream uptake, with Simulium responsible for 91% of the total invertebrate ingestion. Adhesion of FLB to the substrate from the water column seemed to be more important than invertebrate consumption in this stream, and one taxon, Simulium, was responsible for most invertebrate consumption of bacteria.