Spatial And Temporal Pattern Of Zooplankton Communities In Sub-lakes Of The Poyang Lake,China

Zooplankton is an important group of aquatic organisms in aquatic ecosystems,which play a key role in the aquatic food web.Zooplankton directly feeding phytoplankton,bacteria and organic debris,and for high trophic predators,zooplankton is its important source of food.Poyang Lake is the largest freshwater lake in China,and list in list of the Ramsar wetlands of international importance,and it`s the largest freshwater fishery producing areas in China.Therefore,protect the health and stability of the Poyang Lake ecosystem is necessary and signality.It is of great practical significance to study the temporal and spatial dynamics of zooplankton community in Poyang Lake by providing a guide to the ecological protection of Poyang Lake and the rational exploitation and utilization of resources.Under the seasonal water level,the Poyang Lake will form a number of independent shallow lakes in the dry season,which plays an important role in maintaining the integrity and species diversity of the Poyang Lake wetland ecosystem.In order to understand the seasonal dynamics,annual variation and spatial distribution characteristics of the zoooplankton community structure,the zooplankton of 9 sub-lakes in the Poyang Lake National Nature Reserve were sampled by month and seasonal in the period of 2012 to 2015.Besides,the spatial distribution of zooplankton community of 9 sub-lakes were studied.The main results are as follows:1.During the period of four-year study,156 species of zooplankton found in Poyang Lake National Nature Reserve.Belonging to 25 families and 65 genera,including rotifers 13families 39 genera 116 species,cladocerans 6 families 13 genera 21 species,and copepods 6families 13 genera 19 species.Compared with the results of other lakes,it found that the connectivity with Yangtze River and lakes is great significance to maintain the high species diversity of zooplankton in Poyang Lake.2.The species composition,density and biomass of zooplankton showed obvious seasonal variation.The number of species in zooplankton was the lowest in spring and the species diversity in spring was significantly lower than that in other seasons.The density has a peak in both summer and autumn,and varied in different years.The biomass of zooplankton had high value in spring,summer and autumn.Density and biomass in winter are the lowest.3.Dominant species of zooplankton have obvious seasonal variation and a certain degree of interannual difference.Keratella cochlearis and Copepod nauplii were dominant in four seasons;Conochilus unicornis was dominant in spring,autumn and winter,and bloom in some special years of spring.Bosmina longirostris is the most dominant species of cladocerans,and has the advantages in spring,summer and autumn.Microcyclops varicans was dominant species in summer,autumn and winter.In addition,the Daphnia pulex,Sinocalanus dorrii,Macrocyclops fuscus dominant in spring only.Small rotifers were mainly composed of the dominant species in summer and autumn.Such as Brachionus,Keratella,Polyarthra and Asplanchna priodonta has a greater dominance in the autumn.In winter,Synchaeta oblonga and Polyarthra dolichoptera were main dominant species.4.The community structure of zooplankton has significant seasonal variation.The results of non-metric multidimensional scale?NMDS?analysis showed that the community structure of zooplankton could be roughly divided into spring community,summer and autumn communities and winter communities.The species composition,density and biomass of zooplankton in spring were different among years,alone clustered in spring community.The zooplankton community structure has high density and high biomass in summer and autumn,and had similar structure among years.The characteristic of zooplankton community in winter was low density and low biomass,and had similar structure among years.5.The zooplankton community structure had obvious interannual variation that associated with the interannual fluctuations variation of water level.There were significant differences in species composition,density and biomass of zooplankton in different years,and Conochilus unicornis bloom occurred in the spring of 2014,that may have been associated with the continuous storage of dry season.In spring of 2015,the density of zooplankton was the lowest due to inflow by the rise of Yangliujin River.In summer,zooplankton has a higher density in high-water years?2012 and 2015?than in low-water years?2013 and 2014?,which are mainly caused by rotifers,and the density of cladocerans and copepods showed contrary changing trend of rotifers.In the autumn,the zooplankton density and biomass in the years of high water level were lower than the low water level,which may have been associated the more fish predator in the lake at high water level.In winter,the interannual variability of water level did not cause changes in species composition,density and biomass of zooplankton.6.Annual zooplankton community study found that different hydrological period has a different zooplankton community structure.Zooplankton communities were similar in high water level?September-October 2014 and June-June 2015?.The low-water-period?January-March 2015?zooplankton had similar community structure,and the community structure was similar in the water-rising period?April-May 2015?and the water-falling period?Novembe-December 2015?,respectively.Monte Carlo test showed that water level,water temperature,dissolved oxygen,turbidity,conductivity,pH and NO₃-N had a significant effect on the community structure of zooplankton?P<0.05?.Redundancy analysis?RDA?indicates that water temperature,water level and turbidity were the principal factors.7.There were significant spatial differences in zooplankton communities between the sub-lakes in summer and autumn.In summer,the sub-lakes were connecting with each other through rivers,and the distribution of zooplankton communities in sub-lakes were main influenced by the rivers.NMDS analysis and community clustering analysis showed that the zooplankton community in the Shahu lake and the Benghu lake which locate in the west bank of the Xiu river were clustered into one group.The other zooplankton communities group including Dahuchi Lakes and Zhonghuchi Lake,which were affected by the Xiu river and Ganjiang river.Changhuchi Lake,Zhonghuchi Lake,Meixihu Lake and Xianghu Lake were main affecting by the Ganjiang River clustered into one group.In the autumn,the sub-lake is isolated from each other,and the zooplankton community structure is not similar to the summer distribution pattern.The Dachahu Lake was directly connecting with the main lake area,and the community structure is significantly different to other sub-lakes.Redundancy analysis showed that the turbidity and water depth were principal factors influence on the zooplankton community in the lake,while the aquaculture behavior in lake has a certain impact to zooplankton community.