Abstract: Reef-associated community such as fish and macrobenthos is an important component of coral reef ecosystems. The information of these communities is essential for a comprehensive assessment of the health status of coral reef ecosystems. Based on video transect method, a survey was conducted to investigate reef-associated fish and macrobenthos at 17 stations of coral reef area in the Yalong Bay, Sanya City, Hainan Province at the end of December 2018. We analyzed the community structure, quantitative distribution and similarity of the fish and macrobenthos, revealed the ecological warning, and put forward the corresponding regulatory suggestions, aiming at protecting and restoring the coral reefs in the Yalong Bay. A total of 35 species, 21 genera and 8 families, mainly composed of families Pomacentridae and Labridae, were recorded at the 12 stations of west bank of the Yalong Bay, Dongpai and Xipai reefs. The average density of fish was 0.20 ind·m^-2. Pomacentrus chrysurus, Stegastes obreptus and Chromis lepidolepis were the dominant species. Fish resource in the Yalong Bay had been declining in the past 15 years and almost exhausted to date. On the other hand, macrobenthos were dominated by soft corals, benthic macroalgae, sea lilies and sea urchins. The quantitative distribution differed across various groups. The abundance of organisms harmful to hermatypic corals, Drupella and Acanthaster planci, were very low and fail to threat the corals. As a whole, the reef-associated fish and macrobenthos community at west bank of the Yalong Bay were quite different from those at Dongpai and Xipai reefs, reflecting differences in the environment features between the shore and offshore reefs. The environmental conditions at the west bank near the mouth of the Yalong Bay may be more similar to the offshore reefs. Due to the relatively higher abundance of benthic macroalgae and the possible eutrophication trend at some stations, keeping the balance between the population of damselfish or other herbivorous fishes and algae is particularly important for restoring and maintaining the health of reef ecosystem in the Yalong Bay. Meanwhile, management of terrigenous nutrients from Qingmei River and other sources was also the key to control the proliferation of macroalgae in the Yalong Bay. Compared with sea cucumber, crinoids were less dependent on benthic macroalgae. There was no significant correlation between hermatypic coral coverage and the quantity of reefassociated macro-organisms, probably due to the severe degradation of coral reefs in the Yalong Bay as well as the relatively low spatial heterogeneity of coral reefs mainly comprising by massive coral species. In order to better protect coral reefs of the Yalong Bay, more attention should be paid on the management of water quality of the Yalong Bay, and the supervision of fishing, diving and other tourism activities. It is necessary to implement a longterm fishing ban for restoration of fish resource immediately and perform a regular monitoring on the population changes of key species.

Key words: Yalong Bay, fish, macroalgae, community structure, ecological balance.