FLOW PREFERENCES OF LARVAL CHIRONOMIDAE (DIPTERA) IN TONGARIRO RIVER, NEW-ZEALAND

Flow preferences of five major chironomid taxa (Cricotopus, Orthocladiinae sp. a, Eukiefferiella, Tanytarsus vespertinus, and Maoridiamesa) were investigated in December 1990 at three sites in Tongariro River, central North island, New Zealand. Exponential polynomial preference curves indicated that most taxa were found predominantly in water less-than-or-equal-to 0.5 m deep when data from all sites were combined (range of conditions sampled = 0. 1- 1.5 m). Cricotopus and Orthocladiinae sp. a appeared to have broad velocity preferences over the range sampled (0.1-1.8 m s-1). In contrast, T. vespertinus had a velocity optimum of 0. 1 m s-1, and Maoridiamesa had an optimum > 1.0 m s-1 at all sites. Abundances of Eukiefferiella were greatest over an intermediate range of velocity conditions (0.7-1.5 m s-1). Mechanisms leading to differences in velocity optima amongst chironomid taxa may include differential oxygen requirements, and changes in food supply. When determining optimal minimum flows for benthic chironomid communities, it may be sufficient to focus on the requirements of taxa such as Maoridiamesa and Tanytarsus vespertinus which appeared to have well-defined and disparate velocity preferences in the main river.