Explore The Distribution Of Fish Of Major Rivers In Beijing With EDNA Metabarcoding

Biodiversity is a hot topic in ecological research.The Living Planet Report 2020 states that global populations of several species have declined by an average of 68 % in less than half a century due to over-activity,with freshwater biodiversity being lost more rapidly than in other ecosystems.As an important component of freshwater organisms,fish have significant ecological and economic value.The conservation of fish diversity is beneficial to the health and stability of water ecosystems.Fish resources are also in sharp decline due to various factors such as water pollution,overfishing,climate change and invasive species.Beijing,as the capital of the country,has a high population density,rapid social and economic development and a high rate of urbanization.And the urbanization which can lead to habitat loss and fragmentation,resulting in the genetic,species and functional homogenization of organisms in the local area,making it urgent to take measures to conserve biodiversity.The prerequisite for conversation is monitoring.Whereas fish diversity was surveyed by destructive habitat and biologic methods previously,such as nets,ground cages and electrofishing.Environmental DNA(eDNA)technology is now used in combination with high-throughput sequencing(eDNA Metabarcoding)to survey fish diversity in water bodies.eDNA technology is used for surveying of rare and endangered species,invasive species,biodiversity and biomass estimation,due to its efficiency,harmless to habitats and organisms,and no need of biometric capabilities.This study investigated fish diversity of three water systems in Beijing in two seasons by eDNA metabarcoding technology.Evaluated the feasibility of using eDNA technology to investigate fish diversity in Beijing.Analyzed the distribution characteristics of fish in three water systems in Beijing.Discussed the main factors affecting fish diversity and distribution in combination with the environmental factors measured.The main study contents and results are as follows.(1)A comparative analysis of the results of the eDNA metabarcoding and ground cage was carried out.It was confirmed that a significantly higher diversity of fish was detected by eDNA metabarcoding than the traditional method.eDNA metabarcoding identified 55 species of fish compared to 35 species by the traditional method.The fish species composition was predominantly Cypriniformes and Perciformes.(2)The correlation between the relative abundance of sequences and the relative abundance of individual fish was carried out.Results of eDNA metabarcoding and capture results of ground cage were correlated.The eDNA metabarcoding technique was found to be viable for surveying fish diversity in Beijing,and subsequent analyses were based on the results of the result of eDNA.(3)The fish diversity and composition of the three water systems were analysed and compared.There were no significant differences in the biological composition and the αdiversity of fish of the three water systems.The dominant species in the three water systems differed obviously.The Beiyun River dominated by pollution-tolerant species and the Chaobai and Daqing River systems dominated by clearwater fish.Further analysis revealed that the abundance of clearwater fish was significantly higher in suburban rivers than in urban rivers.(4)The analysis compared the fish diversity and composition of the two seasons.There was no significant difference in fish species diversity between the two seasons.But fish family diversity was significantly higher in autumn than in summer,and all cold-water fish identified by eDNA metabarcoding were in autumn.Both indicating that the eDNA metabarcoding technique can be used to assess seasonal changes in fish communities in Beijing.(5)Analysis the effects of environmental factors on fish diversity and distribution.The environmental factors measured did not have a significant effect on the overall fish diversity.However,the distribution of clearwater fish is more influenced by total dissolved solids and conductivity in summer,and mainly by altitude and temperature in autumn.And the fish are distributed in areas of high dissolved oxygen and high altitude in both seasons.Exploring the correlation between the richness of clearwater fish and environmental factors and the night light index.It was found that the diversity of clearwater fish decreased significantly with the increase in total dissolved solids and human activities.Those indicate the impact of urbanization and human activities on the decline of clearwater fish diversity.This study determined the feasibility of using eDNA metabarcoding technology for surveying fish diversity in Beijing.eDNA metabarcoding technology was used to analyse the distribution and seasonal variation of fish diversity in major rivers of Beijing.It provides new proof on the impact of urbanization on biodiversity.A methodological reference for monitoring the biology and a data reference of fish in Beijing also be offered.