THE CHARACTERISTICS OF SPECIES COMPOSITION AND SUCCESSION OF CORAL REEF FISHES IN XISHA EAST ISLAND

The East Island is the second largest island of Xisha Islands, which is a typical coral reef island, and the coral reef is known as the tropical rain forest in the ocean and high biodiversity. In order to better protect and manage the coral reef fish resources in East Island, we investigated the coral reef fish through underwater video and underwater diving fishing, and systematically discussed the species composition and historical evolution characteristics of coral reef fish in combination with historical research in 2021 and 2022. The results were as follows, at present, 235 species of coral reef fish were found in the East Island, belonging to Osteichthys (222 species) and Chondrichthyes (13 species), which were composed of 16 orders and 55 families, of which Perciformes had the largest number of 181 species, and Chaetodontidae and Scaridae had the largest number of 22 species. The correlation between the number of fish species in the coral reef of East Island and its corresponding maximum total length index decreased significantly with the increase of the maximum total length. Small-sized fish was the most common in East Island, accounting for 38.72% of the total species; the second was medium-sized fish, 34.47%; 26.81% of large-sized fish. According to the type of feeding habits, East Island had the largest number of carnivorous fish, 133 species, accounting for 56.60% of the total species; there was little difference between omnivorous and herbivorous fishes, which were 52 and 50 species respectively. From the perspective of similarity, the similarity index between different time periods was low, which confirmed that fish had undergone great succession changes. The comparison between this study and the historical survey shows that there were 103 species of fish that had not been found, especially carnivorous fish, accounting for 74.76% of the undiscovered fish; in this study, 40 species of undiscovered large-sized fish were almost all carnivorous fish, both of which indicate that fish are overfishing. At the same time, 14 species of fish in the coral reef of East Island were listed in the IUCN Red List. Except for one species, others were not found in this study, and all were large fish, which supported the theory that large fish were easy to be extinct. 70.97% of the undiscovered small fish species were reef fish, and long spined starfish were found, both of which indicate that the coral reef waters of East Island were also affected by habitat degradation. The results of this study provide a basic reference for the succession trend of coral reef fish and basic data for the restoration, protection and management of coral reef ecosystem.