Stream food web fueled by methane-derived carbon

Abstract

Food webs driven by energy from the oxidation of methane are now recognized to be omnipresent in terrestrial and freshwater ecosystems (e.g. lakes, soils and peat bogs), as well as in deep-sea hydrothermal vents and cold seeps. However, the incorporation of methane-derived carbon into stream food webs has never been reported. Here we present the first circumstantial evidence from stable carbon and nitrogen isotope ratios that a stream food web composed of aquatic macroinvertebrates is partly sustained by methanotrophs or chemoautotrophs that gain carbon respired by methane-oxidizing bacteria. Methane-derived carbon seems to enter stream communities around anoxic habitats such as backwater pools and hyporheic zones. Because these reductive habitats exist in many streams, food webs partly sustained by methane-derived carbon are likely to be ubiquitous in lotic ecosystems.

Differential assimilation of methanotrophic and chemoautotrophic bacteria by lake chironomid larvae

“…The stable sulphur isotope data suggest that C. anthracinus may actually be rather reliant on chemoautotrophic bacteria, reflected in the lighter δ 34 S values exhibited by this species. In that case, light δ 13 C values may not represent such an important dietary contribution from methanotrophic bacterial biomass, as previously suggested by Kelly et al (2004), but simply reflect assimilation of respired carbon (sensu Kohzu et al 2004). The isotope data do not preclude assimilation from methanotrophs, rather, that relative to its congener, C. anthracinus assimilates a greater dietary proportion from chemoautotrophs.…”

“…However, rather than assimilating carbon partly from a methanotrophic source and partly from an algal or detrital source, as assumed in the mixing models used by Kelly et al (2004), chironomids and zooplankton could exhibit isotopic signatures between -50 and -40 ‰ via consumption of chemoautotrophs that have assimilated respired carbon, as outlined by Kohzu et al (2004). Briefly, this results either from the oxidation of methane (Hollander & Smith 2001) or indeed in high respiration dominated systems, where δ 13 C values of dissolved inorganic carbon may approach -20 ‰, then further fractionation by chemoautotrophs such as sulphur oxidising bacteria results in bacterial δ 13 C between -50 and -40 ‰ (e.g.…”

Possible sources of methane-derived carbon for chironomid larvae

“…The larval δ 13 C signatures of -46 to -55 ‰ in Holzsee in August 2003 (Eller et al 2005) indicate a methanederived carbon source, because CO 2 recycling in general usually results in δ 13 C signatures not lower than -40 to -45 ‰ (Freeman et al 1990, Hollander & Smith 2001. However, this methane-derived carbon source does not need to be MOB biomass, but could also be biomass of autotrophic bacteria, which assimilate the CO 2 released by MOB (Kohzu et al 2004). These autotrophic microorganisms growing close to MOB on the 13 C-depleted methane-derived CO 2 should have a more negative biomass δ 13 C than would be expected for autotrophic bacteria growing on recycled photosynthetic CO 2 .…”

“…Especially larvae of the species Chironomus plumosus showed strongly 13 C-depleted signatures, with values ranging from -40 to -75 ‰ (Grey et al 2004a,b, Kelly et al 2004, Deines & Grey 2006, Deines et al 2007). For larvae with δ 13 C signatures below -45 ‰, biogenic methane is the only component hitherto known to be depleted enough in its 13 C content to be a possible food source for these larvae (Freeman et al 1990, Hollander & Smith 2001, Kohzu et al 2004). Thus, carbon stable isotope analysis led to the hypothesis that these larvae assimilated a dietary food source based on biogenic methane, indicating an unexpected importance of methane-derived carbon for freshwater food webs.…”

Dual processes for cross-boundary subsidies: incorporation of nutrients from reef-derived kelp into a seagrass ecosystem

“…Terrestrial-derived litter drives secondary production in many streams (e.g. Wallace et al 1999, Kohzu et al 2004) and contributes to food webs in fjords (McLeod & Wing 2007), while marinederived macrophytes can drive production on beaches and islands (Polis et al 1997) and in surf and intertidal zones (e.g. Bustamante et al 1995, Crawley et al 2009).…”