Spatial variation in the trophic base of the trichopteran filter feeder Stenopsyche marmorata in an intermittent river in Japan

Abstract

Carbon and nitrogen stable isotope analyses were used to determine how a trichopteran filter feeder Stenopsyche marmorata Navas (Stenopsychidae) reflects shifts in food sources (sus- pended particulate organic matter (SPOM), benthic particulate organic matter (BPOM), and periphy- ton) in response to channel drying in the alluvial soils of the Inukami River in Japan. The δ 13 C and δ 15 N values of consumers shifted to a pattern similar to that of BPOM in an intermittent river, which sug- gests that particulate organic matter at each station may play an important role as a food source. More- over, analysis of the upper reaches of the dry channel revealed that both consumers and food sources have enriched δ 13 C values due to physicochemical characteristics in the channel such as a high water temperatures and stagnant water. Conversely, the lower reaches showed more negative δ 13 C values, suggesting either a lack of carbon or a reduced supply of terrestrial dissolved carbon, both caused by channel drying, and higher δ 15 N values, suggesting a high dissolved inorganic nitrogen concentration in groundwater. Our study showed that a dry channel may influence the flow of energy between consumers and their food sources and the flow of nutrients from the upper to the lower reaches.