Population Growth of Daphnia Pulex (Cladocera) on a Mixed Diet (Microcystis Aeruginosa with Chlorella or Scenedesmus)

Abstract

We quantified population growth of Daphnia pulex on diets of Mlcrocystls aeruglnosa mixed with Chlorella vulgarts or Scenedesmus acutus (0, 25, 50, 75, or 100% cyanobacteria with either algal species, based on equal biomass (dry weight)). We also evaluated the possible adaptations of D. pulex to cyanobacteria when previously grown on a mixture of M. aeruglnosa and Chlorella or Scenedesmus. When offered alone, M. aeruglnosa did not support the population growth of D. pulex for long, while the two algal species promoted population abundance of the daphniid. In terms of population growth, S. acutus was the better of the two algal species. When mixed with C. vulgaris or S. acutus, M. aeruglnosa supported the population growth of Daphnia better than when offered alone. However, regardless of the proportion of the mixed diet, S. acutus with M. aeruglnosa supported population growth in D. pulex better than did a mixture of Chlorella and Mlcrocystls. The rate of population increase (r) per day obtained for D. pulex varied from 0.003 to 0.21, depending on the type of diet. When cultured on a mixed diet, regardless of the algal species involved, D. pulex showed decreased growth rates with an increasing proportion of Mlcrocystls. D. pulex, previously reared on a mixed diet (M. aeruglnosa with Chlorella or Scenedesmus in different proportions), did not grow when transferred to M. aeruglnosa alone, and even began to decline starting directly from the beginning of the experiment. Our results suggest that, together with a species of green alga, the single-celled, toxic M. aeruglnosa could be used for culturing D. pulex.