Litter patch types determine macroinvertebrate assemblages in pools of a Japanese headwater stream

摘要

In forested streams, litter patches are important microhabitats for macroinvertebrates, and the nature of litter patches can affect structure and function of macroinvertebrate assemblages. We examined whether litter patch types with different characteristics could be predicted by their location within stream pools (pool middle, alcove, edge) and, if so, whether patch types had different macroinvertebrate assemblages. Mean mass of leaves per unit area of streambed was 2 to 3x higher in edge patches than in other patches, whereas mean mass of wood and small litter particles was 2 to 6x higher in middle patches. Densities of nemourid stonefly taxa were higher in edge patches than other patches, with density of Nemoura being highly correlated with leaf mass, whereas densities of lepidostomatid caddisfly taxa were higher in middle patches, with density of Goerodes complicatus being highly correlated with mass of small litter particles. Mean biomass and annual secondary production of shredders, collectors, and predators were 1.6 to 4x higher in middle patches than in other patches. Our results indicate that macroinvertebrate community structure and production may differ within and among forested streams according to relative composition of litter patch types, even if overall litter abundance is similar.