## 3 Results  
### Comparative Estimation of Coastal biota between eDNA Metabarcoding and CMI  
A variety of plankton communities were observed through the two identification methods in Gwangyang Bay. There were differences in the number of identified communities between the two methods (Table 1). In terms of quantity, eDNA metabarcoding seemed to be capable of detecting more species. The average numbers of observed (identified and unidentified) species from the eDNA samples were 27.9 (min to max: 20-36) in June and 49.8 (min to max: 13-72) in September, while those from the CMI were 19.6 (min to max: 12-23) and 18.9 (min to max: 12-24), in June and September, respectively (Table 1). Albeit comparing only with the identified species, we found that the number of species was higher in the eDNA samples than the CMI. On the other hand, in terms of the capability of identification of the eDNA metabarcoding, the unidentified species groups comprised 38% in June and 19% in September (Table 1). Accordingly, in Gwangyang Bay, the eDNA samples identified more species in a higher proportion in September. In the eDNA samples, the richness values in September were as twice high as those in June (Table 1). The number of identified species was lower in June (mean \(\pm\) S.D. : 20.2 \(\pm\) 3.3) than in September (\(41.7\pm 15.6\)), which was quite consistent across the study sites. In addition, this pattern was similarly observed from diversity values of the eDNA samples (averages: 1.0 in June and 2.0 in September). The spatial variation of the richness was also lower in June (coefficient of variation: ca. 15%) than in September (ca. 40%). Namely, the heterogeneity of plankton distribution became large in late summer. On the contrary, in the CMI samples, the species richness did not differ between early and late summer; the values of mean and S.D. were 19.6 \(\pm\) 3.1 in June, and 18.9 \(\pm\) 3.5 in September. Notably, the level of diversity was comparatively higher in June (2.3 \(\pm\) 0.2) than in September (1.6 \(\pm\) 0.2), which was counter to the diversity pattern from the eDNA samples. Considered as a whole, the temporal changesof biological communities seem to be more distinct, compared to their spatial variation. Nonetheless, we also note some discrepancy of the results in diversity between the two identification methods. To evaluate the consistency of detection and identification of marine plankton groups, we compared the differences of community composition between eDNA and CMI samples (Figure 3a,b). Although various groups were detected by eDNA metabarcoding, the community composition was based on the identified groups in eDNA samples, in comparison with those from the CMI samples. In the higher rank of taxonomical classification (>phylum), the eDNA samples comprised 28% of phytoplankton (i.e., algae) and 15% of zooplankton (i.e., Copepoda) (Figure 3a), whereas the CMI samples showed 64% of zooplankton (Figure 3b). In the eDNA samples, the dominant groups in phytoplankton were diatoms (e.g., _Thalassioira_ spp.) and dinoflagellates (_Hematodinium_ spp.). In zooplankton, the dominant groups were marine calanoid copepods such as _Acartia_ spp. and _Centropages_ spp. in Gwangyang Bay. Crustacea occupied 17% of the identified species, and were primarily comprised of Amphipoda (e.g., _Carpella_ spp. ), Cirripedia (e.g., barnacles), and Decapoda (e.g., _Caroplium_ spp.). Cnidaria and Mollusca also engaged species richness of 24% in our study area (Figure 3a). The former consisted mainly of small polyp stony coral, such as _Acropora_ spp., and the latter mostly comprised bivalves, such as _Crassostrea_ spp. and _Musculista_ spp. In addition, several groups, which were relatively low proportionally in CMI, were also well identified, including Annelida (5%), Chaetognatha (4%), Echinorma (3%), and fish (4%). Particularly for fish, the identification of fish species was quite limited in the eDNA samples, and hence only three genera were identified (_Arnoglossus_, _Engraulis_, and _Oryza_ spp.).