The inhibitory effect of mixotrophic Ochromonas gloeopara on the survival and reproduction of Daphnia similoides sinensis

Mixotrophs account for a high proportion (occasionally up to 80%) of the phytoplankton biomass. Chrysophyte is one major component of mixotrophs. Because of their possible toxicity and linkage between microbial community and higher trophic levels, the effect of mixotrophic golden algae on potential grazers received much attention. The present study investigated the effect of Ochromonas gloeopara at different proportions in diet (combined with Scenedesmus obliquus ) on the life history of Daphnia similoides sinensis . Results showed that osmotrophically grown O. gloeopara in light produced fish toxins and hemolysins, and negatively influenced the survival and reproduction of D. similoides sinensis . The mortality of the cladoceran increased as the proportion of O. gloeopara in food increased. The D. similoides sinensis could not reproduce throughout the life when Ochromonas comprised above 35%. When fed foods containing 15% of Ochromonas , the time to first brood of D. similoides sinensis was prolonged, together with the reduced number of offspring in first brood and total number of broods. Replacement by 100% S. obliquus delayed the time to death, but did not improve the reproduction of Daphnia . The present study indicated the strong inhibitory effect of O. gloeopara on D. similoides sinensis , and underlined the importance of evaluating its ecological role in aquatic ecosystems.