The potential of methanotrophic bacteria to compensate for food quantity or food quality limitations in Daphnia

The endpoint of anaerobic degradation of organic compounds in aquatic ecosystems methane. This methane-carbon is not necessarily lost for ecosystem processes as it can be utilized methane-oxidizing bacteria (MOB), and possibly recycled into benthic and pelagic food. The dominant zooplankton in many lakes are daphnids, which could act as vectors for channeling-carbon from methanotrophic bacteria upwards in the food chain. We demonstrate, 13C-enriched diets in laboratory experiments, that methane-carbon can enter the food web via filtration of MOB by cladoceran zooplankton. Because carbon use efficiency Daphnia appears to be limited by the availability of dietary sterols on prokaryotic diets, we test hypothesis that the uptake of MOB, the only prokaryotes possessing sterols and sterol-like, can lead to a quantitative and qualitative upgrading of phytoplankton diets of Daphnia. results confirm the general superiority of eukaryotic over prokaryotic food sources for growth and reproduction. Although MOB addition compensated for limited food quantity, found no evidence for a qualitative upgrading through MOB. Consequently, there was no relationship between the quantity of food available and the fitness (somatic growth) of, but rather a strong food quality effect, independent of MOB addition. Our findings support view that methane is an important carbon source to pelagic ecosystems and thus have implications for qualitative and quantitative assessments of carbon recycling pathways in ecosystems