The macroinvertebrate fauna of a New Zealand forest stream

The distribution, abundance, and life histories of benthic invertebrates were investigated in a small, Nothofagus forest stream in North Canterbury, South Island, New Zealand. The fauna was dominated by Trichoptera and Plecoptera; Mollusca and fish were absent. Large particle detritivores and scrapers were the predominant functional groups found. Larval Philopotamidae (Trichoptera) were the only abundant filter feeders. Nymphs of the stonefly Spaniocerca zelandica and of mayflies, Deleatidium spp., were the most abundant animals on plant detritus; Deleatidium spp. were abundant on stones also. The distribution of invertebrates in riffles, loose stones, pools, and plunge pools was examined using mesh colonisation trays lifted in September, November, February, and May after respectively 88, 69, 98, and 94 days in situ. Most species were widely distributed, and sample densities of the more abundant insect species showed weak positive correlations with the biomass of detritus present in trays in most months. The turbellarian Neppia montana was overrepresented in trays compared with stream samples, but the relative abundance of most other species appeared to be similar to that on the stream bed. A large amount of silt accumulated in trays during a heavy flood, and was colonised mainly by the oligochaete Eiseniella tetraedra. Information on the life histories of 15 species of Plecoptera, Trichoptera, Ephemeroptera, and Coleoptera was obtained from a 1‐year monthly sampling programme, in which 36 taxa were distinguished, and from collections of adult insects made over a 3–4‐year period. Most species had poorly synchronised life histories, in that a wide size range was apparent among individuals in most months. Eight species emerged in at least 4 months; S. zelandica and the philopotamid Hydrobiosella stenocerca were taken in 8 and 9 months respectively.