Characterisation and classification of benthic invertebrate communities in 88 New Zealand rivers in relation to environmental factors

Abstract

Benthic macroinvertebrates were sampled (seven Surber samples per site) in 88 rivers throughout New Zealand in “runs” (velocity 0.4–0.8 m s⁻¹, depth = 0.3–0.6 m), under autumn baseflow conditions (Q < median). Medians and 10–90 percentiles for the following community level characteristics were: taxa richness, 14 and 7–20(0.7 m⁻²); Shannon Diversity (H’), 1.33and 0.80–1.90; total density, 1900 and 230–6700 m⁻²; and total biomass, 0.608 and 0.112–2.932 g AFDW m⁻². Invertebrate abundance and taxonomic richness were lowest in rivers with beds of silt or sand, or cobbles overlain with sand deposits. Comparisons of environmental factors between sites grouped by TWINSPAN indicated that the degree of catchment development to improved pasture, water temperature, and level of enrichment (indicated by increased nutrients and periphyton biomass) are important factors affecting invertebrate community structure in New Zealand rivers. Mayflies, stoneflies, and predatory caddisflies were associated with cooler, less enriched, steeper, and more elevated sites than snails, crustaceans, chironomids, and worms. Stonefly biomass was minimal at sites having mean annual temperatures >13°C. The following community characteristics emerged as useful indicators of the level of water enrichment: the Macroinvertebrate Community Index (MCI) and its quantitative analog (QMCI); the presence of some species (e.g., Zelandoperla decorata and Bereoptera roria), and the densities of some widely distributed taxa (e.g., Deleatidium spp. and Psilochorema spp.); percentage predator biomass; and the number of ephemeropteran, plecopteran, and trichopteran taxa (EPT). Sites did not separate out clearly into ecoregions, although rivers with “clean‐water” faunas were more predominant in the South Island than in the North Island. This is thought to reflect the greater degree of development of the North Island catchments.