International Journal of Marine Science, 2025, Vol.15, No.2, 65-74 http://www.aquapublisher.com/index.php/ijms 66 This study will explore the research progress on the biodiversity characteristics and ecological functions of fish species in Hainan Island and coral reefs in the South China Sea. This study will analyze the species composition patterns, community distribution patterns and their functional roles in maintaining the homeostasis of coral reefs, and identify natural and anthropogenic driving factors such as habitat heterogeneity, water quality parameters and fishing pressure. This study aims to analyze the latest research findings, clarify the fundamental role of fish diversity conservation in the sustainable management of coral reefs, provide scientific basis for the construction of regional ecological protection networks and the restoration of degraded habitats, and through interdisciplinary data integration, guide policy-making and protection practices to achieve the long-term maintenance of coral reef ecosystem service functions. 2 Research Progress on the Biodiversity of Coral Reef Fish 2.1 A multi-functional group composed of 800 species of fish The sea area between Hainan Island and the South China Sea is rich in coral reef fish resources. Existing data indicate that more than 800 species of coral reef fish are distributed in this area (Xi et al., 2022; Zhang et al., 2023). These species cover multiple functional groups such as herbivorous species, carnivorous species, planktonic carnivorous species and omnivorous species, and maintain the homeostasis and resilience of coral reef systems through niche differentiation (Luo et al., 2023). Taking the coastal area of Hainan Island as an example, the study has identified 363 species of fish belonging to 114 families and 24 orders. Among them, the Perciformes occupy the dominant group, confirming the taxonomic diversity characteristics of this area. This diversity feature not only represents the regional ecological value, but also supports the complex interaction network of coral-fish communities. Coral reef fish significantly affect system health and productivity levels through key roles such as nutrient regeneration, algal regulation, and habitat construction (Xi et al., 2022; Huang et al., 2024). Empirical studies have shown that the diversity index of fish communities is significantly correlated with the complexity of coral base structures, further verifying the ecological necessity of biodiversity conservation. 2.2 Spatial heterogeneity characteristics of diverse distribution The fish diversity of coral reefs in Hainan Island and the South China Sea shows significant spatial differentiation, which is reflected in the gradient differences between the nearshore and the open sea and between the north and south sea areas. DNA barcoding studies have shown that there are significant differences in the composition of fish communities in the northern and southern sea areas of Hainan Island, with common species accounting for only a minority (Zhang et al., 2023). Synchronous monitoring shows that the fish biomass and community abundance in the nearshore waters of southwestern Hainan are higher than those in other areas, and there are seasonal and spatial dynamic fluctuations (Luo et al., 2023). The eDNA survey on the coral reefs of Xi Island detected 41 species of fish belonging to 16 families, revealing the regulatory effect of local habitat conditions on diversity distribution (Xi et al., 2022). This spatial pattern is driven by multiple factors such as the complexity of coral structure, water quality parameters and the intensity of human activities, resulting in the formation of characteristic fish combinations in different reef areas. 2.3 The combined effect of environmental disturbances and human activities Marine environmental parameters (such as water temperature fluctuations, salinity gradient changes and upwelling events) have a significant regulatory effect on fish diversity. Take the Qiongdong upwelling as an example. Although the special water mass environment formed by it provides a thermal refuge for some species, the algal outbreak and the simplification of habitat structure have led to a sharp decline in fish abundance and community reconfiguration (Zhu et al., 2022). The degradation of coral skeletons caused by large-scale bleaching events further reduces habitat heterogeneity and reef-dwelling species richness (Huang et al., 2024). Human activities such as high-intensity fishing operations, coastal engineering construction and pollution emissions are the main causes of biodiversity decline. The disturbed area shows a trend of community
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