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 speci es of cladocerans measuring (adult mean length (Am) standard error): Daphni a pulex (2413 +/- 129), Moina macrocopa (1286 +/- 49) and Ceriodaphnia dubi a (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 a n increase in the abundance of D. pulex. The response of the other two spec ies to Chlorella and Microcystis differed greatly. M. macrocopa showed incr eased population abundance with increasing Chlorella levels but crashed com pletely when fed Microcystis on day 2. On the other hand, the population de nsities of C. dubia showed an inverse relation with Chlorella levels but in creased 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 Micro cystis. 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 p eak population densities between D. pulex fed Chlorella or Microcystis, but the differences were significant for Moina and Ceriodaphnia. We found no c lear relation between the body size of cladocerans and their ability to con sume Microcystis cells, although D. pulex consistently grew well on either Chlorella or microcystis.