International Journal of Marine Science, 2025, Vol.15, No.3, 118-129 http://www.aquapublisher.com/index.php/ijms 121 at present, it can be foreseen that as the methods become more mature, more eDNA monitoring cases will appear in the future for fish diversity in Hawaii coral reefs. 3.1.2 Monitoring of fish community structure in coral reefs in Okinawa, Japan Okinawa is located in the Ryukyu Islands in the Western Pacific and has a subtropical coral reef ecology similar to Hainan Island. As early as the late 2010s, Japanese scholars had conducted eDNA research on fish in coral reef lagoons in Okinawa. Oka et al. (2021) conducted eDNA monitoring in a small coral reef lagoon in the northern part of Okinawa's main island and detected 291 species of fish (including bony and cartilage fish), far exceeding the 217 species recorded in traditional fishing surveys, adding dozens of species that had not been recorded before. This study is the world's first case of using eDNA for fish biodiversity surveys in tropical coral reef lagoons, demonstrating that eDNA metabarcoding technology can achieve good results in highly species-rich coral reef environments. The study also found significant differences in the composition of eDNA species at different sampling points, indicating that there may be microhabitat differentiation within the lagoon, such as higher proportion of reef fish detected near coral-rich areas, while the proportion of oceanic migratory fish appearing near the outsea channel increases (Oka et al., 2021). Another Japanese team used eDNA to monitor reef-making corals on the slopes of Okinawa's coral reefs. Yoshida et al. (2022) reported the identification of the presence of multiple coral genus using eDNA around the main island of Okinawa, partly a hidden species not recorded in traditional investigations, indicating that eDNA also has potential in the monitoring of the diversity of corals itself (Yoshida et al., 2022). 3.2 Analysis of the adaptability of technology in different sea areas Environmental DNA technology has been applied in various waters from tropical to temperate zones, and the environmental characteristics of different sea areas have an impact on the effect of eDNA detection. In areas with gentle water flow and strong enclosure (such as lagoons and lagoons), eDNA can often retain local information better, and species detection is highly corresponding to on-site communities. On the contrary, in the open sea, currents and tides will rapidly dilute and spread DNA, reducing the sensitivity of local detection. Therefore, the application of eDNA in different sea areas requires consideration of the influence of hydrodynamic factors. Gelis et al. (2021)'s study in the coral triangular area of Indonesia showed that in coral reef bays with relatively stable water flow, the fish community structure detected by eDNA is highly consistent with the survey results of traditional fish fried fish, and can reflect the diversity and dominant species composition of the reef area; while on the outer slopes of the reef with high waves and rapid flow, the number of sampling times is needed to capture instantaneous species signals (Gelis et al., 2021). For Hainan Island, strong water flow disturbances caused by summer typhoons and monsoons may temporarily reduce the eDNA detection rate, while calm seasons are conducive to DNA accumulation and detection. In terms of cross-sea comparison, Mathon et al. (2022) analyzed eDNA monitoring of multiple coral reefs in the Atlantic and Indo-Pacific Oceans and found that although the species composition varies greatly in different regions, the biogeographic pattern revealed by eDNA is consistent with the understanding of traditional diving surveys. This shows that eDNA technology has consistent applicability across regions and can reveal large-scale biodiversity patterns. It is worth mentioning that in some special sea areas such as the deep sea and the polar regions, the application of eDNA is also being explored. For shallow sea ecosystems such as coral reefs, there is sufficient evidence that eDNA can adapt to conditions of different water temperatures, salinity and habitat complexity (Malik et al., 2025). 3.3 Comparison between traditional survey methods and eDNA technology As application cases increase, researchers began to systematically compare the similarities and differences between eDNA and traditional surveys to evaluate the advantages and limitations of new technologies. Overall, most studies have found that the number of species detected by eDNA methods is no less than that of traditional methods, and the detection rate for certain occult and rare species is higher. Gold et al. (2021) compared eDNA with diving surveys in the protected areas of the Channel Islands in California, USA, and found that the eDNA method captured about 76% of the species in visual surveys, and also detected 23 additional fish that were not observed in the naked eye but existed in historical records (Gold et al., 2021). This suggests that eDNA can
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