## 3 Results
### Comparative Estimation of Coastal biota between eDNA Metabarcoding and CMI
By comparison, the CMI samples showed different proportion in species richness (Figure 3b). The main composition (64%) of zooplankton comprised Cladocera (e.g., _Evadne_ spp. and _Podon leuckart_) as well as Copepoda (e.g., 15 calanoid species and three cyclopod species). Conversely, a limited number of phytoplankton was identified in the CMI samples, compared to the eDNA samples. The identified phytoplankton were mostly dinoflagellates which were mainly _Noctiluca scintillans_. Crustacea occupied 11% of species richness. Similar to the identified species from the eDNA samples, they were primarily composed of Amphipoda, Cirripedia, and Decapoda. However, most of them were in forms of larvae which was unable to be identified specifically in the CMI samples. Other specific groups were observed \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**June**} & \multicolumn{3}{c}{**September**} \\ \cline{2-7}  & \multicolumn{2}{c}{**eDNA**} & \multicolumn{2}{c}{**CMI**} & \multicolumn{2}{c}{**eDNA**} & \multicolumn{2}{c}{**CMI**} \\ \hline
**Site** & **Richness** & **Diversity** & **Richness** & **Diversity** & **Richness** & **Diversity** & **Richness** & **Diversity** \\ \hline GY1 & 28 (6) & 1.01 & 23 & 2.37 & 54 (9) & 1.99 & 20 & 1.62 \\ GY2 & 28 (7) & 1.65 & 23 & 2.43 & 59 (10) & 2.39 & 17 & 1.54 \\ GY3 & 20 (5) & 1.08 & 23 & 2.55 & 34 (5) & 1.50 & 12 & 1.34 \\ GY4 & 23 (6) & 1.35 & 22 & 2.46 & 72 (11) & 2.66 & 16 & 1.70 \\ GY5 & 25 (7) & 1.18 & 22 & 2.36 & 44 (7) & 1.65 & 13 & 1.35 \\ GY6 & 22 (6) & 0.72 & 20 & 2.33 & 62 (8) & 2.13 & 19 & 1.55 \\ GY7 & 29 (8) & 0.87 & 12 & 1.96 & 13 (3) & 0.24 & 18 & 1.78 \\ GY8 & 33 (10) & 1.08 & 18 & 2.24 & 29 (6) & 1.91 & 23 & 1.90 \\ GY9 & 35 (11) & 1.59 & 22 & 2.48 & 58 (8) & 2.31 & 24 & 1.61 \\ GY10 & 27 (8) & 1.05 & 20 & 2.37 & 48 (10) & 2.44 & 18 & 1.41 \\ GY11 & 36 (11) & 1.50 & 16 & 1.92 & 72 (11) & 2.69 & 18 & 1.72 \\ GY12 & 34 (10) & 0.56 & 18 & 2.31 & 35 (4) & 2.02 & 20 & 1.61 \\ GY13 & 31 (8) & 0.73 & 18 & 2.38 & 46 (8) & 1.57 & 23 & 1.81 \\ GY14 & 24 (6) & 0.64 & 18 & 1.75 & 45 (9) & 1.96 & 22 & 1.99 \\ GY15 & 24 (7) & 0.70 & 19 & 2.05 & 64 (12) & 2.20 & 20 & 1.66 \\ Mean & 27.9 (7.7) & 1.0 & 19.6 & 2.3 & 49.7 (8.1) & 2.0 & 18.9 & 1.6 \\ S.D. & 5.0 (1.9) & 0.4 & 3.1 & 0.2 & 17.8 (2.7) & 0.6 & 3.5 & 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Richness and Shannon diversity of the samples between water eDNA and conventional microscopic identification (CMI) in Gwangyang Bay. The numbers in the brackets indicate the number of unidentified groups. in a small proportion (3%: Annelida, Chaetognatha, Cnidaria, and Echinoderma, and 5%: Fish and Mollusca, see Figure 3b). Nevertheless, in a finer resolution, there was some commonality of species groups between eDNA and CMI samples (Table 2). In both samples, several genera including _Acartia, Acropora_ and _Centropages_, were commonly observed. At the Gwangyang Bay, _Acartia_ spp. were commonly predominant in early summer, while _Centropages_ spp. were relatively predominant in late summer. _Acropora_ spp. were primarily observed from the eDNA samples around the inner bay in early summer. At the outer bay, including at site 14 and site 15, a dinoflagellate group of _Hematodinium_ was relatively abundant, especially in the eDNA samples. In contrast, _Hematodinium_ was not detected by CMI in the same area. Moreover, _Oithona_ spp. were most predominant in this area, but were relatively less abundant in the outer bay, compared to the inner bay. Figure 3: Community composition from the samples between (**a**) eDNA metabarcoding and (**b**) conventional microscopy identification (CMI). The scatter plots indicate the relationships between species richness and Shannon–Weaver diversity on (**c**) eDNA, (**d**) CMI, and those (**e**) between richness and (**f**) between diversity of the two methods, respectively.