Sea trout, the anadromous ecotype of the species Salmo trutta , are subject to multiple threats, including exploitation and aquaculture impacts in the marine environment, habitat fragmentation and pollution in freshwaters, loss of genetic resilience due to interbreeding with hatchery strains and environmental change. Small streams contribute relatively little biomass to European sea trout stocks but are thought to be important...

Body mass–abundance ( M‐N ) allometries provide a key measure of community structure, and deviations from scaling predictions could reveal how cross‐ecosystem subsidies alter food webs. For 31 streams across the UK, we tested the hypothesis that linear log‐log M‐N scaling is shallower than that predicted by allometric scaling theory when top predators have access to allochthonous prey. These streams all contained a common and...

Methane oxidation produces biomass that is a potential source of particulate carbon for consumers, and is in addition to photosynthetic production. We assessed methanotrophy and photosynthetic production under differing conditions of light and methane concentration. We measured methane oxidation and photosynthesis in gravel sediments from adjacent shaded and unshaded stretches of 15 chalk rivers in southern England, and also i...

Temporal variation in the baseline stable carbon isotope ( δ 13 C) value of a well‐studied, productive lake was examined over a 26‐yr period using archived samples of the herbivorous zooplankter Daphnia galeata as a proxy because of its phytoplankton diet. The baseline δ 13 C value was strongly correlated with pH and the concentration of dissolved carbon dioxide in the lake as well as with the δ 13 C value of a predatory zoopl...

Due to a combination of local methanogenesis and high background concentrations in the groundwater, water in the River Lambourn is 51 times supersaturated with methane (162 nmol CH 4 L −1 ). Pore‐water concentrations of methane in the gravels of the riverbed were much lower throughout the year (71 nmol CH 4 L −1 ), suggesting significant methane oxidation. To investigate the potential for methane oxidation as a novel chemosynt...

We measured the δ 13 C values of dominant primary consumers and their potential food sources in a groundwater‐fed lowland river. The δ 13 C of most consumers, such as Gammarus and Simulium , reflected that of the dominant forms of photosynthetic production, whereas the cased larvae of two caddis flies ( Agapetus and Silo ) were consistently 13 C depleted (mean δ 13 C: ‐41.2% and ‐40.4%, respectively) throughout the year. The r...

We tested the hypothesis that low stable carbon isotope (δ 13 C) values commonly observed for zooplankton in humic lakes are due to their feeding on isotopically light methane‐oxidizing microbes, and thus that methane‐derived carbon is important in the food webs of these lakes. In replicate laboratory cultures, Daphnia longispina , a common crustacean zooplankter in humic lakes, were fed microbial suspensions with or without e...

Stable isotope analyses of chironomid trophic interactions have recently indicated the potential importance of isotopically light biogenic methane as a carbon source. Mass balance of isotope ratios suggests that small proportional differences in ingestion of such an isotopically distinct basal resource by individual consumers can result in considerable intraspecific variability. To test this, we collected individual larvae of...

Seasonal variations in the stable isotope composition (d 13 C and d 15 C) of crustacean zooplankton and their putative food sources in oligotrophic Loch Ness were recorded during 1998. Bulk particulate organic matter (POM) showed d 13 C values consistent with a terrestrial plant origin from the catchment and exhibited little seasonal variation, whereas POM d 15 was more variable, probably due to associated microbial action. In...