An Enclosure Experiment Study of Daphnia galeata Grazing Effects on Phytoplankton in a Subtropical Reservoir
南亚热带水库中盔形蟤牧食对浮游植物群落影响的围隔试验

In order to understand the possibility of suppression of Daphnia on phytoplankton in tropical and subtropical reservoirs,we carried out a fish-free enclosure experiment in Liuxihe Reservoir,southern China from March 6 to April 18,2010,lasting for 6 weeks.The experiment had one control(C) group without adding D.galeata and three treatment groups(L,M,H) with adding low,middle and high density of D.galeata.The adding density of D.galeata was 0 ind./L in C,0.3 ind./L in L,0.6 ind./L in M and 1.0 ind./L in H.Each treatment had 3 replicates.The results showed that the density of D.galeata increased rapidly in all the treatments,and there was no significant difference between the control and treatment groups.The density of D.galeata reached the peak in the third week and then decreased quickly.Correspondingly,the biomass of phytoplankton decreased in the first two weeks and had significant shift on community structure.The biomass of the size class with diameter < 30 μm decreased with the increased of D.galeata.The size class with diameter > 30 μm increased towards the end of the experiment.These results indicate that when D.galeata appears abundantly in the tropical and subtropical deep and oligotrophical reservoirs,it is possible to suppress phytoplankton by means of manipulating density of planktivorous fish.