Common Freshwater Flatworms And Their Potential Effect On Cladocera Community In Reservoirs Of South China

To know common species of freshwater flatworms in South China and their potential effect on Cladocera community, flatworms in diverse water bodies in Guangzhou were sampled from April to September in 2014, and an enclosure experiment was carried out in Liuxihe Reservoir(South China), in which 12 enclosures were used in two groups: six for control and six for nutrients addition, respectively.In total, thirty-one species of flatworms was identified from Tricladida, Macrostomida,Rhabdocoda, Catenulida and Prolecithphora. Gyratrix Hermaphroditus and Macrostomum tuba were the common species in urban lakes, Dugesia in pond, Stenostomum in wetlands,Mesostoma cf. productum and Stenostomum in the Liuxihe Reservoir. According to the observation of flatworms feeding and dissection, we found that flatworms are able to feed on cladocerans, rotifers and copepods, but they preferred to prey cladocerans. Flatworms affected zooplankton community mainly by predating on cladoceran, especially, on some easily handled(or eatable) those species with large body and low swimming speed, for example, species in Daphnia and Moina in the present experiment. Some rotifer species in high density can be captured but are able to escape evenly inside the flatworms. Mesostoma cf. productum was the dominant planktonic species in the experimental enclosures, and it was more abundant in the six nutrient addition enclosures than in the control enclosures. In the nutrient addition enclosures,Mesostoma cf. productum predated selectively on Daphnia galeata, Ceriodaphnia cornuta and Moina micrura, and offered a chance for rotifers to be abundant. In the control enclosures, when Mesostoma cf. productum depressed the eatable Cladocera and increased the uneatable Cladocera abundance instead of the abundance of rotifers, but in some cases the abundance of rotifers increased when the uneatable Cladocera more or less decreased. As population of pelagic flatworms can rapidly increase to high density and their occurrence and density appeared very randomly in all the experimental enclosures, the significant flatworm effect was found but with low explanatory proportion of the total variation of Cladocera community using pooled data of all enclosures. When the flatworms at a high density, however, they strongly effected Cladocera population and zooplankton community.