Methane as a source of carbon and energy for chironomid larvae
In recent years it has become increasingly apparent that the microbial loop and microbial production play an important role in many aquatic ecosystems. Microorganisms decompose and thereby recycle organic material in the water column and the sediment, which would otherwise be lost from the food web. Decomposition of organic matter takes place in aerobic and anaerobic sediments of lakes and wetlands, with anaerobic regions representing the sites for methane production. It is estimated that methane oxidising bacteria (MOB, methanotrophs) consume more than 90% of the methane available. Thus, MOB represent a significant pathway for the recycling of methane carbon back into aquatic food webs. Possible sites of trophic transfer are the oxic-anoxic boundary layers in the sediment or the water-sediment interfaces. The results presented in this thesis looked at this specific habitat in lakes. I particularly focused on interactions between sediment-dwelling chironomid larvae and the methane carbon cycle. For the first time I showed experimentally that chironomid larvae can feed directly on MOB biomass and thus include high amounts of methane-derived carbon into their diet. This thesis also emphasises that the contribution of methane carbon to larval diet can vary during the year and is strongly influenced by lake characteristics, specifically by depth. Moreover I applied a multiple stable isotope approach to unravel complexities in benthic food webs. The results of this thesis show that methane is not only an important carbon and energy source for aquatic benthic macroinvertebrates but could also substantially fuel terrestrial and riparian food webs.