Biodiversity of stream invertebrate faunas in a Waikato hill-country catchment in relation to land use

Abstract

Stream invertebrates were collected from 24 sites surrounded by a mixture of native forest and pasture in the Mangaotama catchment near Hamilton, Waikato, between 1992 and 1999. Sampling methods used included Surber sampling for benthic invertebrates, pump sampling, freeze coring and colonisation baskets for hyporheic invertebrates, and light, sticky and Malaise trapping for winged adults.A total of 188 stream invertebrate taxa were identified during the course of this work, the greatest number reported for any catchment in New Zealand. Of these, 85% were insects comprising largely Trichoptera (68 taxa or 36%), followed by Diptera (40 taxa, 21%) and then Ephemeroptera (23 taxa, 12%). Light-trapping in summer on four occasions coupled with benthic sampling once in summer yielded 81% of total recorded taxa. Streams that drained catchments entirely in pasture or native forest had similar percentages of total invertebrate taxa, and of the Coleoptera, Diptera and Ephemeroptera faunas. However, native forest sites had lower percentages of Mollusca and “other” taxa, and more Trichoptera, Plecoptera and Crustacea taxa than pasture sites. Stream invertebrate distributional patterns in the Mangaotama catchment suggest changes in community composition and loss of some species adapted to forest cover in catchments converted entirely to pasture.