Distribution of rotifer assemblages in North Island, New Zealand, lakes: relationships to environmental and historical factors

1. The geographical distribution of planktonic rotifer species was investigated in 31 lakes in the North Island of New Zealand. 2. A total of 78 species was recorded. Species richness, previously thought to be low in New Zealand, was found to be comparable with that of northern temperate lakes with an average of 21.1 species found per lake. The large, deep oligotrophic Lake Taupo had the lowest richness and the artificial reservoirs the highest. 3. The distribution of species, investigated using multivariate techniques [Cluster analysis, canonical correspondence analysis (CCA)], was most strongly associated with trophic state gradients. For example, Conochilus unicornis, C. dossuarius and Ascomorpha ovalis were associated with more oligotrophic conditions, and Brachionus budapestinensis, B. calyciflorus and Keratella tropica with more eutrophic conditions. Inorganic turbidity was also of importance in determining rotifer distributions in some shallower lakes. 4. Some species, for example K. australis and C. exigus, appear to be limited in distribution by poor dispersal abilities.