Abstract: The ecosystems of South China Sea islands and reefs play a pivotal role in safeguarding national sovereignty and ecological security through their high biodiversity and unique ecological service functions. This paper explores the interaction and ecological functions between seagrass meadows and coral reefs in these regions. Research indicates that under natural conditions, healthy seagrass meadows and coral reefs form a significant pattern of mutualistic coexistence. Seagrass meadows trap suspended particulate matter, provide spawning and nursery grounds for adjacent coral reef fishes, elevate seawater pH, and reduce levels of potential pathogens; these functions effectively mitigate environmental stressors on neighboring corals and enhance ecosystem productivity and biodiversity. Furthermore, the composite ecosystem formed by both provides irreplaceable synergistic effects in dissipating wave energy, preventing coastal erosion, and maintaining the geomorphological stability of islands and reefs. Consequently, it is recommended that the protection and restoration strategies for South China Sea islands and reefs shift from single-target management to a holistic framework of synergistic "coral-seagrass" protection. By protecting and recovering such composite ecosystems, the ecological resilience of the reef systems against global climate change can be significantly enhanced.

Key words: South China Sea islands and reefs, Coral reefs, Seagrass meadows, Mutualism, Synergistic protection