A high sedimentation event caused by dredging and dumping of sediment was recorded on Xiaodonghai Reef in Yulin Bay, southern Hainan Island, China. Significantly high sedimentation and constant light shading were observed during the sediment dumping event (SD Event). Using long-term video transects, we quantified coral community changes and responses to the SD Event between 2008 and 2010. The SD Event caused severe coral mortality on Xiaodonghai Reef at a depth of 6 m, while corals at 3 m were less affected. Total live coral cover at 6 m decreased from 54.3% to 14.8%, and Diploastrea heliopora replaced Galaxea fascicularis as the dominant coral species at 6 and 9 m. The density of juvenile corals also declined after the SD Event, especially for the genera Galaxea and Platygyra. However, the density of juvenile Porites and Pocillopora spp. slightly increased. Monitoring for 11 months after the SD Event indicated no recovery of coral communities on Xiaodonghai Reef. Long-term video transect data also revealed that mean live coral cover dramatically declined, from 30.5% in 2008 to 9% in 2010, while the dominant corals in Yulin Bay shifted to more tolerant coral species, such as massive Porites spp. and D. heliopora. The rapid coral community degradation in Yulin Bay between 2008 and 2010 was probably caused by high sediment deposition resulting from intensive dredging and land-clearing activities. These results highlight the necessity for an integrated watershed management to control sediment deposition on near-shore coral reefs. Of the 704 scleractinian coral species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction [3]. Scleractinian coral communities are sensitive to many disturbances, such as thermal stress [4,5], ocean acidification [6], outbreaks of crown-of-thorns starfish (COTS; Acanthaster planci) [7,8], overfishing [9], typhoon damage [9] and terrestrial pollution [10]. Coral bleaching and ocean acidification resulting from climate change have become the main threats to coral reef on a global scale, whereas on regional scales, terrestrial pollution (especially heavy sedimentation) has become the main threat to inshore coral reefs [6,11,12]. Heavy sedimentation may result in light shading, sediment abrasion on the coral surface, smothering of coral tissues and may eventually lead to its death [13,14]. Heavy sedimentation results in fewer coral species, less live coral, lower coral growth rates, reduced coral recruitment, decreased calcification, decreased net productivity of corals, and slower rates of reef accretion