Leaf litter characteristics affect colonisation by stream invertebrates and growth of Olinga feredayi (Trichoptera: Conoesucidae)

The influences of leaf characteristics on stream invertebrate communities were investigated to improve the basis for selecting plants for riparian management to enhance stream invertebrate abundance and biodiversity. Invertebrate colonisation of leaves of five native and five exotic riparian plants were compared over 4 months in field experiments in a New Zealand pasture stream and adjacent channels, and laboratory experiments were carried out on the leaf preferences and effects on growth of the larvae of Olinga feredayi. Plastic strips and leaves enhanced average invertebrate species richness on tiles in streamside channels by 35 and 68%, and density by 50 and 140%, respectively, indicating that both food and physical habitat contribute to leaf pack effects of increased invertebrate abundance and species richness. Densities of total invertebrates and collector-browsers on leaf packs after 15 days in the streamside channels were positively correlated with leaf % leaching and microbial respiration, and negatively correlated with leaf carbon : nitrogen (C:N) ratio and toughness. Filter-feeding invertebrates showed opposite relationships. Growth of O. feredayi larvae on conditioned leaves was negatively correlated with initial leaf C:N ratio, and positively correlated with colonisation preferences of larvae presented with a range of conditioned leaves. These findings provide improved guidance as to which riparian plants to select to optimise the benefits of litter inputs for stream invertebrates.