International Journal of Marine Science, 2025, Vol.15, No.2, 65-74 http://www.aquapublisher.com/index.php/ijms 67 homogeneity, and the proportion of small and low economic value fish has increased significantly (Lu et al., 2020; Luo et al., 2023; Yu et al., 2024). It is worth noting that some areas still maintain a relatively high ecological integrity, highlighting the effectiveness of targeted conservation measures in alleviating environmental stress. 3 The Ecological Functions of Coral Reef Fish 3.1 Multiple nutritional levels synergistically support energy transfer and structural homeostasis Coral reef fish cover multiple trophic levels from primary consumers (such as herbivorous species) to top predators, forming the basic framework of energy transfer in the ecosystem. Take herbivorous fish as an example. They constitute the main biomass components, drive biomass turnover and nutrient regeneration, and are the core elements for maintaining the fishery productivity and nutrient cascade effect of coral reefs (Robinson et al., 2023). The dynamic balance of multiple nutrient groups ensures the stability of the ecosystem. When coral coverage fluctuates or the environment is disturbed, it will trigger the biomass and structural reorganization of the groups, thereby affecting the overall health status of the system (Russ et al., 2020). The nutritional structure characteristics of fish are closely related to the health of coral substrates. High integrity coral cover areas support higher diversity and biomass levels, while disturbances such as whiteout events or overfishing will disrupt the nutrient network, resulting in decreased energy transfer efficiency and weakened system resilience. Therefore, maintaining the diverse combination of fish at multiple trophic levels is the key to achieving the structural and functional integrity of coral reefs. 3.2 Clean symbiosis and algal regulatory functions maintain the health of corals Coral fish directly promote coral health and enhance interspecies interactions through specialized ecological functions. The cleaning behavior is manifested as specific fish eliminating parasites, necrotic tissues and mucus on the body surface of the host. This process not only provides nutritional supplementation for the cleaners, but also improves the survival rate of the host and enhances the stability of the community (Dunkley et al., 2018). Such interactions have highly selective characteristics. Some cleaning species specifically serve specific hosts or adjust the cleaning strategy according to the environmental gradient (Wu et al., 2024). Parrofish, spiny fish and other herbivorous fish regulate algal biomass through continuous feeding to avoid competition for light resources between corals and algae (Clements et al., 2016; Topor et al., 2019). Such grazing behaviors create substrate conditions for the attachment of coral larvae, while nest-building activities promote biodiversity through microhabitat modification. The functional synergy supports the stress resistance of corals and maintains the complex interspecies interaction network. 3.3 Nutrient cycling and carbon sink functions enhance ecological connectivity Coral fish dominate the nutrient cycle process through metabolic activities. Its excreta are rich in macronutrients and micronutrients. The excretion characteristics of species at different trophic levels vary significantly. These nutrients play a decisive role in the physiological metabolism and systemic productivity of corals. Species diversity guarantees the heterogeneity of nutrient supply and meets the metabolic requirements of corals and other organisms (Figure 1) (Van Wert et al., 2023; Robinson et al., 2023). Fish activities also promote carbon storage and ecological connectivity through cross-habitat migration. Its feeding and migration behaviors accelerate the transreef transport of energy and matter, while the processes of nutrition and carbon cycling directly affect the succession direction of benthic communities and the system's anti-interference ability (Pellowe et al., 2024). Therefore, scientific management of coral reef fish communities is of core value for maintaining their ecological functions. 4 Threats to the Functions of Coral Reef Fish 4.1 Ecological damage effects of illegal fishing operations Illegal operations such as blast fishing and cyanide fishing pose a devastating threat to coral reef systems. Such methods directly damage the coral skeleton structure, dismantle the fish habitats, and lead to the acute extinction of both target and non-target species. Cyanide not only causes momentary coma or death of fish, but also the
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