Response of metazoan zooplankton communities to ecological restoration in a tropical shallow lake

Abstract

The metazoan zooplankton communities were dominated by small cladocerans and rotifers, often lack of large-sized zooplankton in tropical lakes and the controlling factors are not clear. Thus it has been questioned if eutrophic lakes can be restored by reducing fish, increasing large-sized metazoan zooplankton, and the top-down control on phytoplankton in the tropics. South Lake from Jinan University, Guangzhou, is a tropic eutrophic shallow lake. The lake was restored via fish removal and plantation of submerged macrophytes in order to improve water quality. We monitored the water quality, metazoan zooplankton communities and fish before and after restoration in order to study the response of metazoan zooplankton communities to the restoration. The results showed that total nitrogen, total phosphorus and chlorophyll-a concentrations decreased significantly and the transparency increased. The abundance and biomass of cladoceran increased, and high numbers of large-sized cladoceran Daphnia pulex were observed shortly after the restoration. The abundance and biomass of copepods had no significant changes. The density of rotifers decreased,but biomass increased. The sizes of metazoan zooplankton and biodiversity increased. The abundance of Daphnia pulex decreased quickly when fish biomass increased, and increased again when fish biomass was reduced later. Therefore, this study suggests that fish is a key factor controlling the population of large-sized zooplankton in tropical shallow lakes. As controlling fish to maintain high densities of large-sized zooplankton is difficult, it is unlikely to achieve a significant improvement in the restoration of tropical lakes using only biomanipulation.