Trophic position and growth stages of Caddisfly (Stenopsyche marmorata Navas) larvae in the Echi River, Japan

We investigated the trophic position of the larval filter-feeding caddisfly species—Stenopsyche marmorata Navas in the Echi River (Japan) using δ¹³C and δ¹⁵N measurements by instar growth stage. We also analyzed δ¹³C and δ¹⁵N of food sources (periphyton and suspended and benthic POM) along the course of the river. The larvae showed some degree of spatial variation in δ¹³C and δ¹⁵N values with a downstream increase in δ¹³C and δ¹⁵N values. Our results demonstrate that the trophic structure of S. marmorata of different larval stages were spatially varying, depending on food sources. Small-sized instars displayed a higher trophic position than larger instars, confirming that their non-selective feeding behavior leads to consumption of items with high δ¹⁵N values according to the spatial distribution of food sources in the riverine system.