Sluggish methane discharge and biological traits of benthic invertebrates in Lake Baikal

The biological traits of invertebrates inhabiting freshwater methane seeps are poorly understood. We analysed the relationship between invertebrate abundance and environmental factors such as methane concentration, location of gas hydrates in sediments, sediment composition, and the total number of microorganisms (TNMs), including methanotrophs. The abundance of invertebrates varied greatly (CV 10–136%) across box core samples and stations. No significant differences ( P > 0.05) in the abundance of invertebrates were found between stations with sluggish methane discharge, methane concentrations, and gas hydrates located deep in sediments (> 70 cm) and the reference stations. The abundance of meio- and macrobenthic invertebrates reached ~ 130,000 ind. m −2 around gas hydrates ~ 30 cm deep in the sediments. The abundance of nematodes significantly depended on the presence of sulfur bacteria and copepod detritus, while oligochaetes were correlated with the TNMs. Amphipod abundance was dependent on the number of methanotrophic bacteria, while ostracods and copepods showed no dependence on the studied biotic factors. Stable isotope analysis of δ 13 C and δ 15 N indicated that oligochaetes and chironomids consumed different proportions of chemosynthetic carbon. Most benthic invertebrates also formed aggregates, possibly enabling the complete utilization of food resources.