International Journal of Marine Science, 2025, Vol.15, No.3, 118-129 http://www.aquapublisher.com/index.php/ijms 118 Feature Review Open Access Applications and Prospects of Environmental DNA (eDNA) Technology for Coral Reef Fish Species Identification in Hainan Island Yanlin Wang1, Haimei Wang2 1 Tropical Animal Resources Research Center, Hainan Institute of Tropical Agricultural Resources, Sanya, 572025, Hainan, China 2 Hainan Institute of Biotechnology, Haikou, 570206, Hainan, China Corresponding author: haimei.wang@hitar.org International Journal of Marine Science, 2025, Vol.15, No.3, doi: 10.5376/ijms.2025.15.0011 Received: 10 Mar., 2025 Accepted: 17 Apr., 2025 Published: 08 May, 2025 Copyright © 2025 Wang and Wang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Wang Y.L., and Wang H.M., 2025, Applications and prospects of environmental DNA (eDNA) technology for coral reef fish species identification in Hainan Island, International Journal of Marine Science, 15(3): 118-129 (doi: 10.5376/ijms.2025.15.0011) Abstract Environmental DNA (eDNA) technology has made its mark in biodiversity monitoring in recent years, providing a new means for traditional coral reef fish surveys. This study takes the identification of coral reef fish species in Hainan Island as the core, and systematically reviews the principles, methods of eDNA technology and its application progress in tropical waters. This paper introduces the current status of coral reef ecosystems in Hainan Island and the limitations of traditional fish monitoring methods, explains the background and advantages of the rise of eDNA technology; analyzes the source, characteristics and stability of eDNA, summarizes the collection and preservation methods of water samples and the standard procedures for DNA extraction, amplification and sequence analysis. On this basis, the development and main achievements of eDNA technology in aquatic ecology research are summarized, including fish diversity monitoring cases in typical coral reefs such as Hawaii and Okinawa, Japan, and the adaptability of applications in different sea areas and differences with traditional methods are compared. By reviewing the current research status of fish diversity in coral reefs in Hainan Island, we pointed out the distribution of key protected species and endemic species and the shortcomings in current monitoring. This study believes that eDNA technology has the advantages of high sensitivity and non-invasiveness, which can effectively make up for the shortcomings of traditional methods and has important application value in the protection and management of fish diversity in Hainan Island coral reefs. Keywords Environmental DNA; Coral reef fish; Species identification; Hainan Island; Biodiversity monitoring; Marine protection 1 Introduction Hainan Island is located in the northern part of the South China Sea and is one of the most concentrated distribution areas of tropical coral reefs in China. Coral reef ecosystems are known as "a tropical rainforest in the ocean" because of their high biodiversity and abundant fishery resources. According to statistics, China's offshore coral reef fish species are extremely abundant, with a total of about 2 855 species, of which more than 400 coral reef fish are recorded around Hainan Island (Shi et al., 2022). As one of the centers of global coral reef biodiversity, the South China Sea has more than 1 120 types of coral reef fish, accounting for about one-third of the world's coral reef fish. These fish species include butterflyfish, damselfish, groupers, and the humphead wrasse (Cheilinus undulatus), many of which are key functional species and economically important species. However, affected by climate change and human activities, Hainan Island coral reefs have experienced coral bleaching and habitat degradation in recent years, and the structure of fish communities has also changed (Huang et al., 2024). Traditional fish diversity monitoring mainly relies on methods such as underwater visual census and net sampling, but there are obvious shortcomings in complex coral reef environments. Visual investigations are often limited by visibility, underwater terrain, and can only observe species with a certain size and daytime activity, and insufficient detection of hidden cave fish and nocturnal species (Dugal et al., 2023). For example, traditional surveys are difficult to spot small fish hiding in the cracks of reefs or night-infested species, and these "hidden biota" may account for a considerable proportion of the diversity of coral reef fish. Secondly, artificial diving surveys are time-consuming and labor-intensive, and are subject to manpower and diving time, making it difficult to achieve large-scale and high-frequency long-term monitoring. In addition, the method of obtaining specimens
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