Study On The Zooplankton Resting Eggs Community Structure In Yangtze River Estuary

The Yangtze River Estuary is the richest biodiversity region in the mid-latitude Pacific.Benefiting from masses of nutrients which brought by surface runoff,monsoon climate and diversified salinity gradients,and zooplankton living in this region consists of complex population,various species and frequently changing dominant species.Among them,most studies on zooplankton in the Yangtze River Estuary focus on community structure and spatio-temporal distribution,and revealing the zooplankton community structure change under the estuary habitat.These studies not only promote the understanding of what zooplankton's role in material circulation and energy transport,also suggest that zooplankton are facing a highly dynamic environment in estuaries.In addition to this,zooplankton community structure influenced by various organisms and non-organisms in different seasonal and spatial,and the number of organisms often increases rapidly,or decreases fleetly or even disappears,and will reappear in a few months late.Resting eggs is one of the survival strategies for zooplankton and other aquatic invertebrates,which avails to survive in adverse environment and stability maintain the long-term population.The production of resting eggs may be induced by high temperature or low temperature,photoperiod or reduction of available food.Further more,about resting eggs studies will help us more comprehensively to understand the structure and function changes of zooplankton community in the Yangtze River Estuary.It was therefore the aim here to explore the species and population structure characteristics of zooplankton resting eggs on time scale in the Yangtze River Estuary,and whether the distribution of resting eggs is related to the sediment and water environment,and if there are differences in the hatching of resting eggs under salinity gradient.Besides,we also analyse the genetic structure of specific species resting eggs and discusses the population structure formed resaons.Focusing on the above scientific problems,this paper has done the following research.Initially,in order to obtain the resting eggs species information,this study adopts single egg DNA barcode classification method,then establish the resting eggs illustration data.Counting of resting eggs in horizontal sediments and sediments cores samples were carried out to obtain the species diversity index of the study community.A total of 19 species of resting eggs were identified,and the results of population analysis of similarity showed that there was no difference in population structure between seasons.The species and density of resting eggs decreased with the increase of offshore distance and sediment depth,and distributed in a specific regional.The density of resting eggs was the highest in winter,and the abundance changed from summer to autumn to winter with increasing-decreasing-increasing fluctuation characteristics.Labidocera rotunda is the dominant resting eggs,which highest density reaching 1.68 ind.g^-1.Secondly,for explore whether the distribution and hatching of resting eggs are related to the physical properties of water environment and sediments,the study region are divided into estuary and outer sea areas,and analyzed from vertical and horizontal aspects respectively.The results demonstrated resting eggs distribution characteristics are affected by a series of environmental parameters and drastic water flow changes.Accordingly,significant environmental factors affecting the distribution of resting eggs are slightly different in different seasons.Among them,environmental factors such as water chlorophyll?,dissolved oxygen content and sediment chlorophyll?have significant indication,and the total interpretation degree of environmental parameters is between 36.5%and 95.2%.Salinity change,as the most obvious environmental factor in estuarine ecosystem,does not affect the distribution characteristics of resting eggs.It may be that resting eggs in the region has a wide range of salinity.Simultaneously,hatching experiment also showed that the correlation between hatching rate and environmental factors in resting eggs was not significant,and the sampling points with high hatching rate gathered at 122.5°E where the light salt water met,and the water depth was 10-30m,with obvious difference in water layer temperature.Finally,the research of resting eggs genetic structure difference adopted by the resting eggs of L.rotunda COI sequences.Whether the unique estuarine ecological environment caused the zooplankton population differentiation in the niche was discussed.The results revealed environmental factors or geographical distance not caused populations difference.Simultaneously,there are high haploid diversity and high nucleic acid diversity in the population.The results of haploid network diagram and pedigree geography analysis show that there is no obvious geographical population distribution structure of Labidocera rotunda,and it is predicted that there are a large number of haploid individuals with differences in the Yangtze River estuary.AMOVA showed that there was no population differentiation in three population combination modes,and the difference of F_ST value among populations was generally small.Neutral detection showed that the population was in a state of rapid expansion,and gene flow communication among populations was frequent.COI diversity of L.rotunda may be caused by two theoretical reasons:the storage effect of resting eggs and individual differences of species.This paper provides basic data for zooplankton resting eggs in the Yangtze River Estuary from three aspects:the distribution,hatching and genetic structure of resting eggs,and reveals the influence differences of environmental factors at different time and space scales.Among them,the contents of resting eggs and genetic structure in cores sediments supplement the research deficiency,but also provide valuable information and new ideas for marine ecosystem research.