The distributions of sediments and its relation to reef water turbidities were investigated in three fringing reefs along the east coast of Ishigaki Island and a patch reef named “Shimobishi” in the lagoon of Sekisei Reef. In order to quantify fine particles in sediments, we employed “SPSS (content of suspended particles in sea sediments)” method, which was originally proposed by Ohmija (1987) for quick assessment of land-derived soil distribution in reef sediments. We found highest SPSS values in a moat and channel bottom of the Miyara Bay and along the northern coast of the Todoroki River mouth in Ishigaki Island. In contrast, SPSS values were low in other three reefs including Yasurazaki, Shiraho and Shimobishi areas. Reef water turbidities showed significant correlation with SPSS values, which suggests that the major cause of reef water turbidities is resuspension of fine particles in the sediments. Accuracy and precision of the measurements can be increased by using a portable turbidimeter in the original SPSS method. The modified method has the potential for applying to a study of under-water light environment, which may influence coral-algal competitions in degrading reef conditions.

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In the present study, the applicability of the continuous monitoring of pH and partial pressure of CO₂ (pCO₂) to the investigations of coral reef community metabolism was examined. Of the four measurable parameters of the aquatic carbonate system, pH, pCO₂, total alkalinity (TA), and total inorganic carbon (TIC), only pH and pCO₂ could be continuously monitoring. Although the values of TA and TIC calculated from the pH and pCO₂ data were not more precise than direct measurements, the continuous monitoring data with high time-resolution were shown to provide good estimations of the changes in CO₂-related variables using the least-squares method. A new equation for estimating inorganic carbon metabolism (precipitation and dissolution of CaCO₃: g) with an initial value of TA and a simplified equation for estimating organic carbon metabolism (photosynthesis and respiration: p) also helped to minimize the uncertainty. A simulation analysis showed that the standard errors for the calculations of the rates of g and p were less than ±5μmol kg^-1 h^-1 when pH (±0.005unit) and pCO₂ (±2μatm) were monitored at 1-min intervals for 1h; this error is comparable to that of the calculations made using direct measurements of TA (±4μmol kg^-1) and TIC (±2μmol kg^-1) at the start and end of monitoring. The pH and pCO₂ monitoring, tested in the present study at the Shiraho coral reef (Ishigaki Island, Japan), resulted in estimates for g and p that were equivalent to those calculated from TA-TIC direct measurements. The continuous monitoring of pH and pCO₂ has been shown both theoretically and experimentally to be adequate for the estimation of coral reef community metabolism.

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The feeding habits of juvenile serranids, Cephalopholis urodeta, were examined on the basis of 104 specimens (≤100mm in total length, TL) collected from coral reef areas at Iriomote Island, Ryukyu Islands, Japan, from May to September between 1998 and 2001. Thirtyone (29.8%) of the specimens collected had empty stomachs, the overall mean stomach fullness index being low (0.94). The most important prey comprised small fishes and shrimps, food preferences not differing among three juvenile size classes (≤60, 61-80 and 81-100mm TL).

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[in Japanese]

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