Effects of methane producers and consumers on the diet of Chironomus larvae in an arctic lake

Up to 40% of methane produced in aquatic systems is oxidized before it is released into the atmosphere. Microbial oxidation of methane is an important sink and potentially an important pathway for the incorporation of detrital carbon into aquatic food webs. In this study, we tested the hypothesis that methane-derived carbon was an important carbon source for Chironomus larvae in a small arctic lake, but that utilization of methane-derived carbon by larvae differed with depth. We found that an order of magnitude more methane was produced at 5m than at 2m. PCR analysis of sediments, found a greater quantity of methanogen DNA at 5m than at 2m, while methanotroph DNA was less common in sediments except for surface sediments. Larval tubes showed a unique composition of methanogen and methanotroph communities when compared to surrounding sediments. A surprisingly larger abundance of methanogens was found in larval hindguts than larval foreguts of Chironomus from deeper sediments. The presence of methanogens and methanotrophs within the larval guts in addition to their depleted delta13 C signature is consistent with our hypothesis that methane-derived carbon is an important basal food resource in this small lake. Furthermore, the combination of biogeochemical and microbial approaches provides insight into functional differences among habitats for a ubiquitous benthic consumer.