INFLUENCE OF THE FILAMENTOUS CYANOBACTERIUM PLANKTOTHRIX AGARDHII ON POPULATION-GROWTH AND REPRODUCTIVE PATTERN OF THE ROTIFER BRACHIONUS-CALYCIFLORUS

The population dynamics of B. calyciflorus was investigated using a gr een alga, Monoraphidium minutum, and a blue-green alga Planktothrix ag ardhii as food sources, separately and as mixtures. Growth rate (r), e gg ratio (ER), and juvenile development time (D-J) were measured in th e laboratory and mortality rate and embryonic development time (D-E) W ere calculated. With M. minutum, Brachionus showed a typical growth cu rve ('Monod-kinetics') dependent on food concentration. In contrast B. calyciflorus did not grow well on P. agardhii. With all food concentr ations the measured growth rates were about r=0. At low food concentra tions r was low with both food types, but the ER of B. calyciflorus wa s significantly higher with P. agardhii as food source. Furthermore th e relative egg volume of females carrying one egg was higher with Plan ktothrix than with Monoraphidium. An addition of P. agardhii to M. min utum led to increasing growth rates. Highest growth rates were found w ith complementary food sources. High food concentrations of M. minutum shortened the juvenile development (D-J) time, but D-J was uneffected by different P. agardhii food concentrations. A mixture of both algae did not shorten D-J compared with M. minutum as single food. The calc ulated D-E was not effected by different food qualities but the calcul ated mortality was nearly 3 times higher with P. agardhii as food.