Response Of Mete-zooplankton Communities To The Ecological Restoration In A Tropical Shallow Lake

Eutrophication is the main problem of lake ecosystems,and one of the main phenomenons of Lake Eutrophication is the proliferation of phytoplankton in a large scale.Meta-zooplankton,especially those large-sized cladocerans are in great expectation and interest in controlling algae.The theory of ecological restoration of lakes which based on the traditional biomanipulation has been widely used in water quality management of lakes in Europe and the United States.At present,the successful cases mainly were found in the temperate regions,the research and exploration of this theory in tropical areas is still in its infancy. Zooplankton in tropic regions is relatively small,and the abundance of large individuals is relatively low,which can not control the phytoplankton efficiently.In temperate regions,fish predation pressure is considered as one of the main reasons for the lower abundance of large individuals and a result of small meta-zooplankton.The abundances of large zooplankton,especially large cladocerans increased significantly after ecological restoration of temperate lakes,which maintained the clear water state of the lake effectively.There is less research about whether the effect of ecological restoration in the tropical regions on the meta-zooplankton is similar to that in the temperate regions.To explore the successions of the meta- zooplankton communities occurred in the ecological restoration of tropical shanllow lakes,in this paper,variations of species composition,abundance,dominant species, and body length changes in frequency of meta-zooplankton communities were investigated in the process of ecological restoration which was carried out in a tropical shallow lake - a subset of Huizhou West Lake-Nanhu Lake.The results are as follows:With the reduction of fish predation pressure,the species of meta-zooplankton in Nanhu Lake increased markedly,the abundance of meta-zooplankton increased rapidly after the removal of fish,but then declined rapidly,thereafter fluctuated at levels lower than before;After the removal of fish in whole lake,the abundance of rotifers declined sharply,some relatively large-sized individuals of cladocerans and copepods appeared,and the body size of the meta-zooplankton community get larger,but compared with temperate lakes,and the abundance is still relatively low,also,no large cladocerans such as Daphnia which can control the algae efficiently appeared.The missing of Daphnia after biomanipulation may be able to explain why the application of the traditional biomanipulation in tropical shallow lakes often fails.The improvement of water quality in Nanhu Lake may not be the result of biomanipulation,but more likely to thank to the reduced disturbance by removal of fish and the restoration of the submerged macrophyte community.Effect of biomanipulation is limited,the combination of pollution controlling,fish manipaltion and restoration of submerged macrophyte community is an effective way to improve water quality of the tropical shallow eutrophication lakes.