Rotifers in relation to littoral ecotone structure in Lake Rotomanuka, North Island, New Zealand

The spatial and temporal dynamics of rotifers in the littoral ecotone of Lake Rotomanuka (37 degrees 55' S, 175 degrees 19' E) were studied from February to November 1994. Rotifers were sampled with artificial substrates at two or three weekly intervals from eight sites chosen with respect to macrophyte species distribution from near shore to deeper water. 58 rotifer species were found, a high diversity in comparison to that of New Zealand limnetic communities, which usually have less than ten species. Rotifers had peak abundances in summer within emergent and submerged vegetation, when shallow regions were dry. Lecane bulla (Gosse) and Testudinella parva (Ternetz) generally had the highest numerical densities. Three major temporal groupings of species were distinguished by cluster analysis and canonical correspondence analysis (CCA): summer-autumn (e.g. Lecane hornemanni (Ehrenberg), L. bulla), winter-spring (e.g. Mytilina mucronata (Muller), Trichocerca porcellus (Gosse)), and late autumn to mid spring (e.g. T. parva, Polyarthra vulgaris (Carlin)). Rotifer species composition appeared to depend on seasonal change of water level and the associated shift from heterogeneous to homogenous physical and chemical conditions across the ecotone. Temporal variability in the abundance of zindividual rotifer species was far greater than their spatial variability. CCA indicated that temperature and pH were the factors most strongly associated with temporal variation in abundances of rotifer species. Macrophytes appeared to play the major role in determining spatial distribution, both because of differences in physical structure between species (affecting microhabitat diversity) and by causing variations in physical and chemical conditions (e.g. oxygen and pH) by inhibiting mixing.