Hydroecology of a New Zealand glacier-fed river: linking longitudinal zonation of physical habitat and macroinvertebrate communities

In comparison to European glacier-fed catchments, the hydroecology of New Zealand glacier-fed rivers has received limited attention, despite the Southern Alps markedly different maritime climate, a more precipitation dominated flow regime and an endemic species assemblage. This study linked longitudinal patterns of the physicochemical habitat and macroinvertebrate community along a New Zealand glacier-fed river and compared and contrasted these with understanding of European alpine river systems. Habitat variables and benthic macroinvertebrates were sampled over two consecutive summer melt periods at three sites along the Rob Roy stream, a tributary of the Matukituki River, in Mt Aspiring National Park near Wanaka, South Island. Although habitat stability increased downstream from the glacier terminus (Site R1), disturbance remained a limiting factor of macroinvertebrate abundance and species richness at the lower sites (R2 and R3). An average water temperature increase of 2 degrees C over 3.3 km (from R1 to R3) was observed downstream with habitat heterogeneity and species richness highest at the downstream site (R3). The ephemeropterans Deleatidium cornutum and Nesameletus dominated at the upper two sites with the chironomids Eukiefferiella and Maoridiamesa, but became co-dominant at R3 with Deleatidium angustum, where other plecopteran and trichopteran taxa were also observed. Distributions were predominantly limited by temperature, thought to be due to adaptation to disturbance observed in taxa of New Zealand alpine streams. However, the plecopteran Zelandobius, although tolerant of cool temperatures, appeared limited to areas and periods when channel stability was higher. Modification of the conceptual model of the longitudinal zonation of macroinvertebrate taxa (Milner et al., 2001a) is proposed to account for the different species assemblage of New Zealand glacier-fed rivers. Copyright (C) 2010 John Wiley & Sons, Ltd.