Associations between environmental variables and zooplankton body masses in a regulated Australian river

An exploratory study was made to investigate the association between mean zooplankton body mass and river environmental variables and also zooplankton biomass in the Hawkesbury-Nepean River over a year. Simple correlation showed that the mean body masses of three zooplankton populations (protists, rotifers and copepods) and of the community (including cladocerans) were correlated significantly with one to three examined variables that tended to intercorrelate. Partial correlation showed that the mean body mass of the zooplankton community was significantly positively correlated with only the community biomass when the effects of other predictor variables were controlled. On a population basis, the mean body mass of rotifers showed a similarly positive correlation with the biomass. The mean body mass of protists was negatively correlated with temperature, whereas the mean body mass of copepods was negatively correlated with fiver flow rate and chlorophyll a concentration. The mean body mass of cladocerans showed no significant correlation with any of the examined variables in both simple and partial correlations. Although the results of this study should be regarded as exploratory, the differing associational patterns indicate that there may be no single mechanism regulating the body sizes of populations and communities of river zooplankton.