A total of 279 specimens belonging to nine species of soft corals of the genus Sarcophyton were subjected to chemical study for the diversity of cembrane diterpenes. Following morphological identification, each specimen was examined for metabolites using gradient HPLC, NMR, and other tools. The S. glaucum and S. cinereum species complex was found to be the most abundant and to contain the most diverse metabolites in the Ryukyu Archipelago, Japan. S. trocheliophorum and S. ehrenbergi were moderately abundant and diverse in metabolites, while other all species seemed to be scarce and restricted in metabolites. During this research we encountered two new compounds (7, 12), whose structures are described in this report.

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Effects of short-term sedimentation on common coastal coral species, Goniastrea aspera, Porites lobata and Pavona frondifera, from the reef flat southeast of the Ryukyu Islands, Okinawa, Japan were investigated in laboratory experiments using oxygen uptake respirometers. The O₂ consumption rate was significantly different among species and between sediment treatments (20 and 200mg l^-1 red soil suspension, P<0.05). In dark experiments, Goniastrea showed higher respiration rates (0.020±0.002ml O₂ cm^-2h^-1) than did Pavona (0.017±0.003mL O₂ cm^-2h^-1) and Porites (0.010±0.001ml O₂ cm^-2h^-1). In light experiments, Goniastrea also showed higher O₂ consumption rates (0.021±0.003ml O₂ cm^-2h^-1) than did Porites (0.010±0.004ml O₂ cm^-2h^-1) and Pavona (0.007±0.001ml O₂ cm^-2h^-1). Zooxanthellae densities were 6.53±0.13, 3.12±0.05, and 4.37±0.07 (×10⁶cells cm^-2; mean±SE, n=8) in Goniastrea, Porites, and Pavona, respectively. Coral respiration rate increased proportionally with zooxanthellae density in Goniastrea and Pavona. High zooxanthellae density may increase the O₂ production that contributes to colony respiration; however, in Porites, the relationship between zooxanthellae density and coral respiration rate was not clear. The massive corals, Goniastrea and Porites, are more resistant to sediment stress than is the plate-like coral, Pavona. Goniastrea showed high tolerance and adaptation to stress conditions in all experiments, at all times (12h), with similar trends in both dark and light conditions. Porites was affected only within the first 3h under light conditions, while Pavona was the most affected species. These results help us to understand coral damage caused by red soil sedimentation, as well as coral mortality and potential shifts in community structure related to prolonged or repeated elevated levels of sedimentation on coastal reefs.

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The Pleistocene Ryukyu Group consisting mainly of reef-complex deposits is exposed in Maeda-misaki area, central part of Okinawa-jima, Ryukyu Islands, southwestern Japan. The Pleistocene sequence, unconformably overlying pre-Tertiary phyllite of the Nago Formation, comprises the Quaternary Ryukyu Group and Holocene beach and alluvial deposits in this area. The Ryukyu Group consists of the Sobe Formation which is unconformably overlain by younger limestones. The Sobe Formation, the main body of the group, reaches 35m in thickness and crops out at elevations of up to 90m. Five lithologic units have been identified in the carbonate sequence of the Sobe Formation in the neighboring area Yomitan and are numbered sequentially from the base upwards (Units 1-5). Of these, four units (Units 2-5) extend in the study area. Unit 2 is composed chiefly of conglomerate and sandy to gravelly limestone. Each of Units 3 and 4 consists of shallow-water coral limestone grading upward into deep-water deposits (rhodolith, Cycloclypeus-Operculina, and detrital limestones). Unit 5 is composed exclusively of coral limestone. The younger limestones are less than 4m in thickness, rest unconformably on the Sobe Formation, and include detrital and coral limestones. These limestones are found at 3 sites at elevations of <-30m on the coast of the study area. The stratigraphic relationship between the detrital and coral limestones remains unknown due to their limited occurrences. Nannofossil biostratigraphy indicates the sandy limestone of Unit 2 of the Sobe Formation ranges in age from 0.41 to 1.65Ma.

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Degradation of coral reef ecosystems are recognized in many areas around the world. Increase of seawater turbidity due to terrigenous sediments is regarded as one of the major cause of the degradation. We investigated levels and temporal variability of the turbidity during a two-year period at Urasoko Bay, a fringing coral reef of Ishigaki Island, Japan. At the near shore station, the median value of the turbidity was 2.26 NTU with the maximum of 92.9 NTU. At the two stations, 150m and 370m offshore, the median values of the turbidity were 0.58 NTU and 0.36 NTU, respectively. Correlation of the turbidity with the precipitation was weak, but wind showed significant correlation with the turbidity. Especially, the wind of the northwestern direction tended to increase the turbidity. These observations suggested that re-suspension of the bottom sediments by the wind driven turbulence and the wind-current with high turbidity and low salinity affected the variability of the turbidity in the Urasoko Bay.

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[in Japanese]

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