Title Page

ABSTRACT

Contents

Chapter 1. Introduction 9

Chapter 2. Materials and Methods 12

2.1. Sample collection 12

2.2. DNA extraction and amplification 14

2.3. Biochemical properties analyze 16

2.4. Bioinformatics 16

2.5. Data analysis 17

Chapter 3. Results 20

3.1. Seasonal distribution of physical and chemical properties 20

3.2. Community composition of Jinhae Bay through eDNA metabarcoding 27

3.3. Effects of hypoxia on community structure 32

3.4. Effects of biogeochemical factors on dominant phylum 41

3.5. WGCNA network construction and key module identification 43

Chapter 4. Discussion 50

Chapter 5. Conclusion 56

References 57

국문초록 63

Table 2.1. CO1 targeting universal primer sequence and Illumina adaptor used in this Study 15

Table 3.1. Alpha diversity and abundance of each metazoan phylum in research period 29

Table 3.2. The ASV annotation, abundance of Arthropoda, and the number of ASVs per each month at before and after hypoxia period in station 4 bottom 40

Table 3.3. The table of ASV composition for each WGCNA module. A few family (Identity 〈 80%) that has been separately identified is written in italic. 45

Figure 2.1. Map of sampling station in Jinhae bay from May to December in 2021 13

Figure 2.2. Scale independence and mean connectivity of station 4 bottom layer. The red line indicates the point at which the scale free topology model fit is 0.9. 18

Figure 3.1. Seasonal variation in temperature, salinity and dissolved oxygen by station and sampling depth observed during research period 21

Figure 3.2. Seasonal variation in ΔTemperature, ΔSalinity, Δ Oxygen and dissolved oxygen in bottom layer by station and observed during research period (delta(Δ) refer difference between... 23

Figure 3.3. Contour map of seasonal DO distribution in Jinhae Bay. The contour interval is 1 mg/L. Thicker line shows the border of hypoxia (2 mg/L) 24

Figure 3.4. Seasonal variation in biochemical factors observed during research period . (PO₄, NO₃, NO₂, NH₄, SiO₂, POC, DOC, Chl-α) 26

Figure 3.5. Sunburst plot of metazoan composition in Jinhae Bay confirmed by environmental DNA metabarcoding 28

Figure 3.6. NMDS plot of metazoan beta diversity by month, sampling depth and station 31

Figure 3.7. NMDS plot of metazoan beta diversity in station 4 bottom layer 33

Figure 3.8. Sunburst plot of metazoan composition in station 4 bottom confirmed by environmental DNA metabarcoding 35

Figure 3.9. Changes in the number of monthly ASVs of the dominant phylum at station 4 bottom 37

Figure 3.10. Correlation between dissolved oxygen concentration and alpha diversity at the Phylum, Class, and Order level in station 4 bottom. Statistically significant values are marked with... 38

Figure 3.11. Correlation between biogeochemical factors and alpha diversity in major phylum in station 4 bottom 42

Figure 3.12. Dendrogram of each ASV classified cluster through WGCNA 44

Figure 3.13. Heatmap of correlation between each WGCNA module and the biogeochemical factor. Statistically significant values are marked with black square. 47

Figure 3.14. Monthly distribution chart of each WGCNA module 49