Abstract: Several parameters including species biodiversity, coverage, diseases, and recruitment of corals were investigated in Houhai waters, Sanya, Hainan, by the manta tow and line intercept transect methods to assess the health status of coral reef ecosystems, and the main factors affecting the health status of coral reef ecosystems were analyzed. The results showed that there were 54 species of scleractinia corals in Houhai waters and the mean coverage of corals reached more than 50%. Few coral diseases and low mortality were observed. The recruitment of corals was very high, up to 4.5 ind·m^-2. The condition index of coral reef ecosystems ranged from 1.75 to 2.27, indicating that the coral reef ecosystems in Houhai waters were in a healthy status. Analysis showed that seagrass bed and seaweed in the shallow area, abundant grazers and the upwelling in summer should be mainly responsible for the healthy status of coral reef ecosystems. Massive seagrass and seaweed distributed in shallow water can absorb the landsourced nutrients and stop the eutrophic water directly into coral reefs in Houhai waters. Abundant grazers such as Diadema setosum mediate the competitive interaction between reefbuilding corals and seaweeds, preventing the seaweed from threatening the growth of corals and preempting the space for coral settlements. The existence of the upwelling in summer maintains the suitable water temperature in Houhai water in summer, avoiding the coral bleaching. Accordingly, the interactions of multiple factors ensure the health of the coral reef ecosystem in Houhai waters.

Key words: ISSR, Isaria cicadae, enzootic, genetic structure