Background Sub-lakes are important for the maintenance of the ecosystem integrity of Lake Poyang, and zooplankton play an important role in its substance and energy flow. Methods A seasonal investigation of zooplankton was conducted in spring (April), summer (July), autumn (October) and winter (January of the following year) from 2012 to 2016 in a sub-lake of Lake Poyang. The aim of the present study was to understand the seasonal dynamics and interannual variation of zooplankton communities and their relationship to environmental factors. Results A total of 115 species were identified in all samples in the four years, which comprised of 87 Rotifera, 13 Cladocera and 15 Copepoda. Rotifera was the dominant group in terms of quantity, and its species richness and abundance were significantly higher when compared to Cladocera and Copepoda (P < 0.05), while Cladocera dominated in terms of biomass. The species richness of Rotifera exhibited a significant seasonal difference (P < 0.05). Both the density and biomass of zooplankton revealed significant seasonal differences (P < 0.05). In general, the density and biomass of zooplankton were higher in summer and autumn, when compared to winter and spring. Biodiversity indices were dramatically lower in spring than in the other seasons. The non-metric multidimensional scaling (NMDS) analysis suggested that these zooplankton communities can be divided into three groups: spring community, summer-autumn community, and winter community. The seasonal succession of zooplankton communities did not have interannual reproducibility. In high water level years, the dominant species of zooplankton (Cladocerans and Copepods) in the wet season had a lower density, and the result in low water level years was exactly the opposite. The redundancy analysis revealed that water temperature (WT), conductivity, pH and dissolved oxygen (DO) had significant effects on the zooplankton community. Conclusions The community structure of zooplankton has a significant seasonal pattern, but has no interannual repeatability. In high water level years, the dominant species of zooplankton (Cladocerans and Copepods) in the wet season had a lower density, and the result in low water level years was exactly the opposite. The density, biomass and diversity indices of zooplankton were significantly different in different seasons. The present study was helpful in the further understanding of the ecosystem stability of lakes connected with rivers, providing scientific guidance for the protection of lake wetlands.

Shallow lakes are important for the maintenance of Lake Poyang ecosystem integrity, and zooplankton play an important role in its substance and energy flow. We investigated zooplankton in spring (April), summer (July), autumn (October) and winter (January of the following year) from 2012 to 2016 in a sub-lake of Lake Poyang with seasonal water level fluctuations. The study aims to understand their seasonal dynamics and interannual variation of zooplankton community in relation to environmental variables. A total of 115 species were identified in all samples of the 4 years, comprising 87 Rotifera, 13 Cladocera and 15 Copepoda. Rotifera was the dominant group in quantity and its species richness and abundance were significantly higher than Cladocera and Copepoda (P<0.05, by ANOVA), while Cladocera dominated in biomass. Species richness of Rotifera showed a significant seasonal difference (P<0.05 by ANOVA). The clear decline of zooplankton species richness in spring was mainly due to the dramatic decrease of Rotifera species. Furthermore, both density and biomass of zooplankton showed significant seasonal differences (P<0.05). Generally, the density and biomass of zooplankton were higher in summer and autumn than in winter and spring. Biodiversity indices e.g., Shannon-Wiener index and evenness were dramatically lower in spring than in other seasons. Non-metric multidimensional scaling (NMDS) analysis suggested that the zooplankton communities can be divided into three groups: spring community, summer–autumn community and winter community associated with distinct indicator species. The results of species richness and community analysis showed that the seasonal succession of zooplankton communities did not have interannual reproducibility. Redundancy analysis revealed that water temperature (WT), conductivity, pH and dissolved oxygen (DO) had significant effects on the zooplankton community. In addition, water level fluctuations, disturbance by wintering waterbirds and artificial water level control during dry season have potential effects on zooplankton community structure too. This study is helpful to further understand the ecosystem stability of lake connected with rivers and provide scientific guidance for protection of lake wetlands.

Shallow lakes are important for the maintenance of Lake Poyang ecosystem integrity, and zooplankton play an important role in its substance and energy flow. We investigated zooplankton in spring (April), summer (July), autumn (October) and winter (January of the following year) from 2012 to 2016 in a sub-lake of Lake Poyang with seasonal water level fluctuations. The study aims to understand their seasonal dynamics and interannual variation of zooplankton community in relation to environmental variables. A total of 115 species were identified in all samples of the 4 years, comprising 87 Rotifera, 13 Cladocera and 15 Copepoda. Rotifera was the dominant group in quantity and its species richness and abundance were significantly higher than Cladocera and Copepoda (P<0.05, by ANOVA), while Cladocera dominated in biomass. Species richness of Rotifera showed a significant seasonal difference (P<0.05 by ANOVA). The clear decline of zooplankton species richness in spring was mainly due to the dramatic decrease of Rotifera species. Furthermore, both density and biomass of zooplankton showed significant seasonal differences (P<0.05). Generally, the density and biomass of zooplankton were higher in summer and autumn than in winter and spring. Biodiversity indices e.g., Shannon-Wiener index and evenness were dramatically lower in spring than in other seasons. Non-metric multidimensional scaling (NMDS) analysis suggested that the zooplankton communities can be divided into three groups: spring community, summer–autumn community and winter community associated with distinct indicator species. The results of species richness and community analysis showed that the seasonal succession of zooplankton communities did not have interannual reproducibility. Redundancy analysis revealed that water temperature (WT), conductivity, pH and dissolved oxygen (DO) had significant effects on the zooplankton community. In addition, water level fluctuations, disturbance by wintering waterbirds and artificial water level control during dry season have potential effects on zooplankton community structure too. This study is helpful to further understand the ecosystem stability of lake connected with rivers and provide scientific guidance for protection of lake wetlands.