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.
LI XiuBaoHUANG HuiLIAN JianShengYANG JianHuiYE ChengCHEN YongQiangHUANG LiangMin
Endosymbiotic dinoflagellates in the genus Symbiodinium are among the most abundant and important group of photosynthetic protists fotmd in coral reef ecosystems. In order to further characterize this diversity and compare with other regions of the Pacific, samples from 44 species ofscleractinian corals representing 20 genera and 9 families, were collected from tropical reefs in southern Hainan Island, China. Denaturing gradient gel electrophoresis fingerprinting of the ribosomal internal transcribed spacer 2 identified 11 genetically distinct Symbiodinium types that have been reported previously. The majority of reef-building coral species （88.6%） harbored only one subcladal type of symbiont, dominated by host-generalist C1 and C3, and was influenced little by the host＇s apparent mode of symbiont acquisition. Some species harbored more than one clade of Symbiodinium （clades C, D） concurrently. Although geographically isolated from the rest of the Pacific, the symbiont diversity in southern Hainan Island was relatively low and similar to both the Great Barrier Reef and Hawaii symbiont assemblages （dominated by clade C Symbiodinium）. These results indicate that a specialist symbiont is not a prerequisite for existence in remote and isolated areas, but additional work in other geographic regions is necessary to test this idea.
