Effects of channel morphology on temporal variation in invertebrate community structure in two North Island, New Zealand rivers

Abstract

Abundance and species composition of benthic invertebrate communities were investigated in two rivers of contrasting channel form, the Tukipo and Waipawa, in the Southern Hawke's Bay, New Zealand. Monthly collections between December 1995 and December 1996 yielded a total of 89 taxa from the two sites; Deleatidium spp. numerically dominating the braided Waipawa whereas Pycnocentrodes spp., Pycnocentria funerea, Aoteapsyche spp., and Elmidae were most common in the constrained Tukipo. Although disturbance frequency was similar between rivers, the streambed substrates were smaller, and hence less stable in the Waipawa. Number of taxa, total abundance, and community composition changed through time in both rivers. The Waipawa community changed least throughout the year; perhaps because of greater numbers of rare taxa at the Tukipo whereas greater resilience of taxa and community dominance by the mobile generalist Deleatidium spp. in the Waipawa lead to greater constancy. At a broader taxonomic scale, invertebrate communities of the Waipawa were also more similar to communities in two South Island braided rivers (Ashley and Rakaia) than the Tukipo. Thus, although braided river communities may show some similarities throughout New Zealand, the community of the constrained channel was clearly different both in taxonomic composition and temporal change of that composition.