Seasonal abundance of small cladocerans in Lake Mangakaware, Waikato, New Zealand

The seasonal changes in the dynamics and life histories of the Cladocera in Lake Mangakaware, North Island, New Zealand, were studied over 19 months b y sampling at weekly or 2-weekly intervals. Lake Mangakaware is a 13.3 ha p olymictic lake with high nutrient status, low Secchi disc transparencies, a nd an unstable thermal regime. The four planktonic cladoceran species (Bosm ina longirostris, B. meridionalis, Ceriodaphnia pulchella, and C. dubia) ex hibited disjunct population maxima. Only B. longirostris was perennially pr esent. All species exhibited low fecundities and low lipid content, indicat ing that food resources were limited and that competitive interactions and resistance to starvation were probably important in determining species suc cess. Increases in body size in cooler seasons were unrelated to clutch siz e, giving further support for the view that available food was limited. The se results are consistent with previous experimental findings that subtle d ifferences in life history can determine seasonal success and the outcome o f competition between similar species.