2011 Volume 5 Pages 21-35
Dietary components of larval chironomid species, Chironomus plumosus, in Lake Izunuma were investigated using carbon stable isotope ratios and fatty acid composition. Carbon stable isotope ratios (δ13C) of the potential foods for the larval chironomids, particulate organic matter (POM) and sediment, were –27.8±1.3‰ and –27.8±0.1‰, respectively. The larval chironomids showed large inter-individual δ13C variation; –50.9 to –27.5‰. Some larvae, which showed similar δ13C values to POM and sediment, were considered to assimilate carbon derived from POM and/or sediment, while others which showed dramatically lower δ13C than POM or sediment were considered to assimilate carbon derived from biogenic methane sources by feeding on methane-oxidizing bacteria (MOB). Fatty acid composition of 4 larval individuals which showed different δ13C levels (–50.9‰, –47.5‰, –36.4‰, –31.7‰) were analyzed. All larvae contained a higher ratio of bacterial fatty acid biomarker i17:0 than did diatoms, green algae, and cyanobacteria. This indicated that bacteria are an important food source for larval chironomids. The content of i17:0 was correlated with larval δ13C. This result suggested that i17:0 was derived from methane-utilizing bacteria such as MOB.
