Species composition and succession of coral reef fishes in Huaguang Reef, Xisha Islands

A list of coral reef fish species of Huaguang Reef was compiled in 2023 using hand fishing, diving fishing, underwater video, and eDNA detection, combined with historical data from 1979 and archival records from the South China Sea Fisheries Research Institute of the Chinese Academy of Fisheries Sciences for the years of 1998, 1999, 2003, and 2005. Successional characteristics of coral reef fishes through time were also explored. The findings revealed: (1) A total of 299 coral reef fish species were identified in Huaguang Reef, categorized into 2 classes, 16 orders, and 56 families, with Perciformes exhibiting the highest species count (234), constituting 78.26% of all species. (2) In comparison to the period of 1979–2005, there was a reduction in the number of species at the order and family levels in 2023 at Huaguang Reef. Both the average taxonomic distinctness (Δ+) and the variation in taxonomic distinctness (Λ+) exhibited a declining trend, indicating disturbances in the fish ecosystem. (3) The proportion of herbivorous fish at Huaguang Reef remained relatively stable in 2023 compared to the 1979–2005 period. Notably, the similarity coefficient of herbivorous fish was the highest among different feeding types, signifying a degraded state of the Huaguang Reef habitat. (4) In contrast to the 1979–2005 period, a significant decline was observed in large-sized and carnivorous fish species at Huaguang Reef in 2023. The low similarity coefficients for both categories, with undiscovered fish species accounting for 58.49% and 45.76% of their respective taxa in the total list, respectively, suggested a notable impact of overfishing on coral reef fishes. The succession patterns revealed in this study provide a theoretical foundation for advancing the sustainable development of coral reef fish resources in the Xisha Islands and offer valuable insights for the protection and management of coral reef fishes.