Zoological Studies

Leaf Breakdown in a Subtropical Stream Riffle and Its Association with Macroinvertebrates

Sen-Her Shieh, Chorng-Bin Hsu, Chiao-Ping Wang, and Ping-Shih Yang (2007) The relationships between the quality of leaves of 3 trees (Machilus thunbergii, Schefflera octophylla, and Ficus erecta) and the assemblages of macroinvertebrates were studied at a riffle section of a 3rd-order subtropical forest stream in northern Taiwan. Macroinvertebrate taxon richness and density that colonized bags of leaves of the 3 tree species did not significantly differ. Macroinvertebrate assemblages were dominated by collectors, such as non-Tanypondinae Chironomidae, Prosimulium spp., and Baetis spp., which constituted > 79% of the total fauna. Results of a principal component analysis (PCA) showed that the macroinvertebrate assemblages were associated with the incubation time of the litter bags in the stream and the fine particulate organic matter (FPOM) trapped by the leaf bags, but not with the variables of leaf litter quality. Shredders, predominantly small nemourids, accounted for only 5.7%, 7.1% and 10.8% of the total macroinvertebrate assemblages on M. thunbergii, S. octophylla, and F. erecta, respectively, suggesting that macroinvertebrates played only a minor role in leaf litter breakdown in this subtropical 3rd-order stream. However, the density of shredders on F. erecta, as a function of the weight of the leaf litter remaining, was significantly higher than that of M. thunbergii, possibly because of the preference of shredders for high-quality food resources. In a comparison with the temperate zone systems, the dominant taxa of shredders that colonized the leaf litter were similar, but their relative abundances were much less in this subtropical forest stream riffle.