Coniferous needle litter acts as a stable food resource for stream detritivores

Abstract

We investigated the diets of stream detritivores in a coniferous plantation and a deciduous-coniferous mixed forest using stable isotope (δ13C and δ15N) mixing models. In summer, collector-gatherers (Ephemera japonica, McLachlan, and Paralichas sp.) and a shredder (Lepidostoma crassicorne, Ulmer) utilized coniferous needle litter but not broad-leaved deciduous litter as their food resource because coniferous litter was persistent and remained on the streambed in both the forests even in summer. In early spring, L. crassicorne in the mixed forest utilized both coniferous needle litter and broad-leaved deciduous litter because both were abundant and available. However, coniferous needle litter was the only dominant food source available for the shredder species in the plantation where deciduous trees were less abundant. E. japonica and a collector-filterer (Hydropsyche sp.) in the forest possibly utilized fine materials derived from coniferous needle litter but not those derived from broad-leaved deciduous litter as their food resource. Although previous studies have indicated that coniferous needle litter is less nutritious than broad-leaved deciduous litter, persistence of the coniferous needle litter provides a stable basal food resource for shredders, collector-gatherers, and collector-filterers in forested streams that receive litter inputs from neighboring conifers.