Insights into the importance of nematode prey for chironomid larvae

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.