Combined effects of colonial size and concentration of Microcystis aeruginosa on the life history traits of Daphnia similoides.

Microcystis colonial size and concentration have detrimental effects on life history traits of Daphnia, but their detailed interactions have remained unclear so far. Our experiments show that the interaction between Microcystis colonial size and concentration on maturation time, life expectancy, net reproductive rate and innate capacity of increase in Daphnia similoides was significant. In all groups, the survival rate of D. similoides was 100% within 8 days. This value then declined quickly in the large-colony groups and in the SH group of Microcystis. Colonial M. aeruginosa significantly reduced the maturation time and body length at maturity of D. similoides. The number of offspring at first reproduction per female in the SH group of Microcystis was significantly higher than those in other groups. Net reproductive rate of D. similoides in the SL group of Microcystis was significantly higher than those in other groups of Microcystis. The innate capacity of increase of D. similoides in small-colony Microcystis groups was significantly higher than that in the large-colony groups. The results suggested that the effect of smallcolony Microcystis on the reproduction of Daphnia was positive under lower concentration, while their toxicity was intensitied under higher concentration when small-colony Microcystis were by Daphnia as food.