Dietary Effect of Heterotrophic Flagellate on Survival, Somatic Growth and Reproduction of Daphnia

Abstract

To evaluate the dietary effect of heterotrophic flagellates on production of cladocerans, we assessed survival, somatic growth and reproduction of Daphnia pulicaria fed heterotrophic flagellate Kinetoplastid. In addition, for comparison to Kinetoplastid, bacteria and Chlorella vulgaris were used as food sources for D. pulicaria. In the food treatment with Kinetoplastid, D. pulicaria did not mature and died within 8 days. The same result was found in the treatment with pure bacterial diet （bacteria 100%）. To compare the somatic growth of D. pulicaria among the food treatments, we calculated increment rate （mm ind.－¹ day－¹） of body length of D. pulicaria from 0 age （day） to maturation or death （the treatments other than pure Chlorella diet, Chlorella 100%）. The increment rate （mm ind.－¹ day－¹） was low in the food treatments with Kinetoplastid as compared with that in the pure Chlorella diet. Our findings have suggested that Kinetoplastid are not necessarily sufficient food source for production of D. pulicaria. The results might be valuable in plankton ecology because information about dietary effect of heterotrophic flagellates on cladocerans has been lacking. The present study indicates that it might be necessary to consider what kind of cladocerans are useful for target reservoirs of biomanipulation to improve water transparency because the genus Daphnia, which is often used in biomanipulation, sometimes decline in the environments with abundant microbial diets （bacteria and heterotrophic flagellates）.