Comparative population dynamics of three species of cladocera in relation to different levels of Chlorella vulgaris and Microcystis aeruginosa

We conducted population growth experiments for 22-30 days using three species of cladocerans measuring (adult mean length (Am) standard error): Daphnia pulex (2413 +/- 129), Moina macrocopa (1286 +/- 49) and Ceriodaphnia dubia (951 +/- 57) fed the green alga Chlorella vulgaris and cells separated by ultrasonic waves of the Cyanobacterium, Microcystis aeruginosa, offered in three densities (0.75 x 10(6), 1.5 x 10(6), and 3.0 x 10(6) cells ml(-1)). An increase in the availability of Chlorella and Microcystis resulted in an increase in the abundance of D. pulex. The response of the other two species to Chlorella and Microcystis differed greatly. M. macrocopa showed increased population abundance with increasing Chlorella levels but crashed completely when fed Microcystis on day 2. On the other hand, the population densities of C. dubia showed an inverse relation with Chlorella levels but increased with increasing levels of Microcystis aeruginosa. C. dubia reached a peak density of 37 +/- 1 ind. ml(-1) at 3.0 x 10(6) cells ml(-1) of Microcystis. Under the same food conditions, D. pulex reached 10 +/- 0.5 ind, ml(-1). The rate of population increase per day (r) was similar (0.24) for D. pulex and M. macrocopa on Chlorella vulgaris at 3.0 x 106 cells ml(-1). No statistically significant differences were detected for r values and the peak population densities between D. pulex fed Chlorella or Microcystis, but the differences were significant for Moina and Ceriodaphnia. We found no clear relation between the body size of cladocerans and their ability to consume Microcystis cells, although D. pulex consistently grew well on either Chlorella or microcystis.