MICROHABITAT PREFERENCES OF BENTHIC INVERTEBRATES AND THE DEVELOPMENT OF GENERALIZED DELEATIDIUM SPP HABITAT SUITABILITY CURVES, APPLIED TO 4 NEW-ZEALAND RIVERS

Microhabitat preferences of 12 benthic invertebrate taxa were investigated in four New Zealand rivers. Most taxa showed significant habitat preferences. Generally, taxa were more abundant in water less than 0.75 m deep and in gravel or coarser substrates, and no taxa showed a clear preference for fine substrate (sand and fine gravel) or deep water. Coloburiscus humeralis, Zelandoperla spp., and Aoteapsyche spp. preferred coarse substrate and water velocities of more than 0.75 m s-1, whereas Nesameletus spp. and Pycnocentrodes spp. were associated with similar substrate but lower water velocities (0.2-0.8 m s-1). Naididae preferred low (< 0.3 m s-1) water velocities, Potamopyrgus antipodarum and Chironomidae low to moderate velocities (0.0-0.75 m s-1), and all three were associated with a broad range of substrates. Deleatidium spp., Olinga feredayi, Hydrobiosidae, and Aphrophila neozelandica were found in a wide range of habitats. Velocity, depth and substrate suitability curves developed for Deleatidium in each of the four rivers also demonstrated the broad habitat tolerances of this genus. Generalised suitability curves formed by enveloping, rather than averaging, curves from each of the rivers performed favourably when compared to models based on suitability curves developed for each river individually. Correlations between Deleatidium abundance and the joint suitability function, calculated from the generalised velocity, depth, and substrate curves, were significant but poor (r = 0.44-0.69) in each of the four rivers. The intercepts of the linear relationships between Deleatidium abundance and the joint preference factor were not significantly different from zero for three of the four rivers, suggesting that the preference functions are applicable to in-stream flow assessments.