Stream faunas and ecoregions in South Island, New Zealand: do they correspond?

Water chemistry and benthic invertebrate communities of 100 headwater streams within 10 South Island, New Zealand, ecoregions were examined to assess the usefulness of ecoregions as a basis for stream classification. Water chemistry did not vary in a systematic manner among ecoregions and showed considerable variation within some of them. In contrast, invertebrate communities differed among ecore­ gions in a much more consistent way. Taxonomic richness, numbers of endemic spe­ cies, species dominance and summer faunal densities all differed among ecoregions, but little discrimination was possible using functional feeding groups. Stream faunas were generally similar between forested ecoregions, whereas the alpine (Southern Alps) ecoregion had the most distinct fauna. Geographically distinct areas that have been deforested and are dominated by tussock grassland and improved pasture now have very similar stream faunas with few regionally distinct elements present. Our results provide qualified support for the use of ecoregions as a basis for stream classi­ fication in New Zealand.