Feeding efficiencies of Chironomus plumosus (L.) and C. anthracinus Zett. (Diptera: Chironomidae) in mesotrophic Lake Erken

Abstract

SUMMARY. Absorption efficiencies of nitrogen and carbon in two Chironomus species found dominating in the profundal zone of mesotrophic Lake Erken were determined gravimetrically. Absorption efficiencies for C. plumosus showed greater seasonal variation than those of C. anthracinus, with low efficiencies coinciding with the summer dominance of flagellate phytoplankton and with high C:N ratios. Overall mean absorption efficiencies (±SE) for carbon and nitrogen, respectively, were 26.8% (±1.9) and 29.3% (±1.9) for C. plumosus, 24.6% (±1.7) and 28.1% (±1.8) for C. anthracinus. Significant differences were found to exist between the C: N ratios of the superficial 2 cm sediment layers and those of Chironomus anterior midgut contents. C. anthracinus appears to be a deposit feeder ingesting particulate matter scraped from the recently deposited surface sediments. The greater seasonal variation found in the absorption efficiencies of C. plumosus, together with the lower C:N ratios, support the contention that this species is a filter feeder with the nutritional quality of ingested matter depending primarily on pelagic inputs.