Effects of reach-scale canopy cover on trophic pathways of caddisfly larvae in a Japanese mountain stream

Differences in trophic pathways between reaches with and without tree canopy cover above the channel were assessed using stable isotopes in a 1.4-km stretch of the Kamo River, Japan. The trophic pathways of two larval trichopteran species, a grazer ( Goera japonica, Goeridae) inhabiting stone surfaces and a net-spinning filter-feeder ( Stenopsyche marmorata, Stenopsychidae) inhabiting interstices of the stony stream bottom, were estimated using carbon and nitrogen isotopes in reaches with and without canopy cover in winter. The delta C-13 values of G. japonica were similar to those of periphyton at each station, suggesting that G. japonica is a grazer on periphyton. A significant positive correlation between carbon isotope values of S. marmorata and benthic particulate organic matter ( BPOM) indicated that BPOM varied in composition according to the amount of solar energy within a reach. In addition, there was a significant positive correlation between carbon isotope values of filter-feeders and the periphytic algal contribution to BPOM using an isotope mixing model, indicating that the main food source of the filter feeders was derived from the in situ periphytic algae in open reaches and from a terrestrial source in canopy-covered reaches.