Differential assimilation of methanotrophic and chemoautotrophic bacteria by lake chironomid larvae

Abstract

Bacteria play an important role in the nutrition of many lake-dwelling detritivorous macroinvertebrates, yet few studies have investigated the roles of differing groups of bacteria in freshwater systems. Recent stable carbon isotope analyses have revealed that methanotrophic bacteria help fuel lake food webs. We analysed individual larvae of co-existing Chironomus plumosus and C. anthracinus for stable sulphur isotopes as an alternative tracer for bacterial assimilation, and compared them with existing stable carbon isotope data. The combination of these 2 isotopes suggests that there are large inter-and intraspecific differences in the incorporation of bacteria rather than algae in the diet of both species. C. anthracinus appears to assimilate a greater proportion of chemoautotrophs relative to its congener, which is consistent with classical descriptions of C. anthracinus feeding mode relative to bacterial stratigraphy in the sediments. The higher intraspecific isotope variability of C. plumosus indicates variable proportions of methanotrophs, chemoautotrophs and phytoplankton to the diets of individuals.

Field Exploration of Methane Seep Near Atqasuk

“…This level is considerably lower than the δ 13 C of the total organic carbon content of the sediment (-30‰) and is in keeping with values that have been taken to indicate consumption of biomass derived from methane oxidation in other lake systems (i.e., Grey et al 2005). Radiocarbon analysis of these live chironomid larvae from the same seep also produced a 14 C "age" of 1,760 years, which supports the role of "old" methane in the diet of these modern benthic invertebrates.…”

The Incredible Lightness of Being Methane-Fuelled: Stable Isotopes Reveal Alternative Energy Pathways in Aquatic Ecosystems and Beyond

“…Hence, the addition of further stable isotopes such as δD [e.g., (Deines et al, 2009;Belle et al, 2015;van Hardenbroek et al, 2016), δ 34 S (Grey and Deines, 2005), and to a certain extent δ 15 N (Stephen et al, 2002;Grey et al, 2004a); see later discussion], have proved useful in ascertaining the use of MDC. Radio isotopes might offer some support under certain situations; for example.…”

Nitrous oxide emission by aquatic macrofauna

“…These worm-shaped larvae often dominate benthic invertebrate communities of freshwater ecosystems and can reach levels of abundance from several hundred to thousands of individuals per square meter (12). The larvae live in U-shaped burrows in the sediment and feed on suspended and settled particulate organic matter, thereby ingesting large numbers of bacteria (13). Our investigation of larvae, dissected guts, dissected gut epithelia, and pupae of C. plumosus unambiguously demonstrated nitrate-dependent denitrification activity and nitrous oxide production associated with bacteria coingested with particulate organic matter (Fig.…”