Insights into the importance of nematode prey for chironomid larvae

Abstract

The potential predatory ability of Chironomus riparius, well-known detritus-feeding chironomid larvae, on nematodes was investigated in a series of laboratory experiments. We analyzed the consumption rate (i) for different prey densities of adult and juvenile Caenorhabditis elegans (25–1200 and 25–2400 prey individuals, respectively), (ii) for different substrates (detritus, sand, and gravel), and (iii) with a natural nematode community as prey. This is the first study to demonstrate a clear predator–prey interaction between chironomids and nematodes. The number of ingested C. elegans increased with increasing prey density. Within 4 h, C. riparius consumed up to 0.77 mg of nematode prey (557 adult individuals), which corresponded to 92.5% of the chironomid’s biomass, and as many as 763 juvenile C. elegans (0.0226 mg; 3.2% of chironomid biomass). Significantly more nematodes were devoured in fine sediment (sand and detritus) than in gravel. Within a natural assemblage, C. riparius consumed 41% of the total nematodes, preferentially those 1- to 2-mm in length; thus, for example, only the percentage of the most common species, Trischistoma monohystera, was significantly reduced. Gut analyses of the chironomids confirmed the ingestion of nematodes. In general, this study provides a fundamental approach to our understanding of the benthic food web.