Diversity of Fish Species in Xixuan Island Coastal Waters Based on Environmental DNA Metabarcoding

Global biodiversity loss is one of the most serious environmental crises of the 20th and 21st centuries. Fish diversity, an important component of biodiversity, is also in decline. The conservation of fish diversity is therefore essential for ecosystem management and the sustainable use of resources. Most current aquatic biodiversity surveys rely on conventional methods. The emergence and application of environmental DNA (eDNA) technology has triggered unprecedented innovations in aquatic organism investigation and monitoring. eDNA metabarcoding refers to the selection of appropriate universal primers for different target taxa and the identification of multiple target species in environmental samples via PCR amplification combined with high-throughput sequencing. The Zhoushan Archipelago, located in the northeastern waters of Zhejiang Province, consists of 2 085 islands with a total area of 22 216 square kilometers. Located at the confluence of the Yangtze River, the Qiantang River, the Yongjiang River, and the Taiwan Warm Current, the Zhoushan Archipelago forms a unique and complex hydrological environment, which provides a rich source of nutrients and a suitable habitat for fish. In recent years, the large-scale exploitation of marine resources and marine pollution have led to a serious loss of fish diversity near the Zhoushan Archipelago. To restore fish diversity, conservation efforts have been implemented by the government and researchers, including stricter fishing bans and ecological fish stock enhancement and release. However, the lack of reliable tools to understand the species and assess biodiversity is the most critical issue in conservation efforts. Trawl sampling and morphological identification are the primary fish diversity assessment methods. However, these conventional methods are often inefficient, time-consuming, selective, and destructive. The extensive rocky reefs in the Zhoushan Archipelago make it difficult to use conventional fishery resource survey methods efficiently. Therefore, simple and accurate methods for species diversity monitoring are needed. In this study, Xixuan Island, an offshore island in Zhoushan, was taken as a reference. Four different sampling stations were designed, and a total of 12 water samples were collected in February, May, and November 2019. The species composition and diversity characteristics of offshore fish communities around Xixuan Island were described, and the spatial and temporal differences in fis