Three species of corals of the family Pocilloporidae, Pocillopora damicornis Linnaeus 1758, Seriatopora hystrix Dana 1864 and Stylophora pistillata Esper 1797 are known to planulate throughout a year in Palau (Atoda 1947a, b, 1951). They are also known to planulate in many other places and their planulation period tends to be longer in the tropical areas than in the areas at higher latitude. This trend was regarded to be regulated by sea water temperature, but also other factors were claimed to work (Harrison and Wallace 1990). We tried to study if temperature is main factor regulating planulation period of the Okinawan population of these species. We made two series of experiments with the coral specimens from Sesoko (26°40′N, 127°50′E), Okinawa, culturing three species from September, 1993 to May, 1995 and S. pistillata from May, 1995 tJune 1996. During these periods P. damicornis was cultured in the first series, and S. pistillata in the second series at both ambient and constant (26°C) temperatures. In order to see the effect of lower temperature than the ambient, P. damicornis was studied at 20°C, 22°C and 24°C. The results showed that planulation of these corals are regulated with temperature and that planultion of P. damicornis takes place at temperatures above 20°C and that of S. hystrix and S. pistillata above 24°C. According to Nishihira and Veron (1995), the northern-most limit of distribution of P. damicornis is Kushimoto (34°N, mean sea water temperature: 22.0°C), that of S. hystrix is Amami Oshima (28°N, 24.5°C) and that of S. pistillata is Amakusa (32°N, 13-27°C) (Ministry of the Environment and Japanese Coral Reef Society 2004). Sea water temperature is cited from Yeemin et al. (1990).

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The relationship between genetically different zooxanthella types and their physiological functions in scleractinian corals has been studied extensively, because decrease in coral abundance is a growing concern at the present and possibilities of changing symbiotic algal partner by corals with more adaptive zooxanthella types against perturbed environment and survival of coral species harboring particular zooxanthella types after environmental changes were suggested. Distribution patterns of algal genotypes have been examined using molecular phylogenetic methods also in the North-West Pacific region, which exhibits a wide latitudinal range (tropical, subtropical, and temperate areas) of scleractinian coral distribution and is an appropriate field to understand adaptive patterns of coral-algae relationship in response to latitudinal changes of environmental factors (e.g. temperature and light intensity). Main clade in the North-West Pacific region is clade C, while clades A and B are dominant in the Caribbean. At a subtype level, several subtypes within clade C are dominant in the North-West Pacific region. Some different algal genotypes have also been found within the same colony or the same species of corals at both clade and subtype levels in the North-West Pacific region. However, some problems have been pointed out in the DGGE (Denatured Gel Gradient Electrophoresis) analysis, which has often been used to determine algal genotypes at a subtype level. Thus the distribution patterns of algal genotypes should be examined further by using the sequence data.

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To investigate the influence of urbanization and coastal development on estuarine and coastal environments in tropical and subtropical settings, sedimentological and geochemical analyses were conducted on river and marine sediments from the Naha City area, the most populated area of Okinawa Prefecture, Japan. Sedimentological and geochemical characteristics of surface sediment samples collected from Naha Harbor and the Kokuba and Asato rivers were compared with those of basin soils and strata to determine the sediment source and contaminant level. Analytical results showed high mud content in the port and lower stream samples, as well as the soil and strata samples, but low mud content in samples from upper stream and offshore sites. The abundance of organic matter was closely related to the mud content. Contents of carbonate and metals characteristic of carbonate minerals were positively correlated with sand content and were enriched in upper stream and offshore samples. Contents of metals characteristic of silicate and clay minerals were high in the port, lower stream, soil, and strata samples; these samples were characterized by high mud contents. Particularly high heavy metal concentrations were found in the port and lower stream samples. Based on principal component analysis, the samples in the study area could be divided into two clear groups: offshore and upper stream samples, which were mainly derived from carbonate minerals, and lower stream, port, soil, and strata samples, which were mainly derived from silicate and clay minerals. The carbonate sediments in the upper stream may reflect the mixing of limestone, used for construction, into river sediments. Sediments from the lower stream and port sites originated from silicate and clay minerals but also contained abundant organic matter and heavy metals, possibly produced by human activity. This result suggests the accumulation of contaminants in the sediments of urban rivers and coastal zones from various sources. Sediments in the offshore sites were predominantly composed of carbonate minerals produced by reef calcifying organisms. There, the inflow of terrigenous muddy sediments was overwhelmed by the in situ production of biogenic carbonate sediments.

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Rapid degradation of coral reefs is a key issue of global concern. Monitoring coral health has been conducted based on observations by divers in various areas. In order to provide a simple instrument to those divers for monitoring coral health, we developed a remote-sensing-based monitoring method that could detect concentrations of symbiotic algae in coral colonies. The spectral reflectance of partly bleached coral colonies were measured in situ by a fiber spectrometer. The normalized difference vegetation index for coral (NDVIc) and the normalized difference coral index (NDCI) were calculated based on the reflectance at red/infrared and blue/infrared wavelength regions, respectively, from various part of colonies. Photosynthetic capacity, measured by the pulse amplitude fluorometer (Diving-PAM) showed a good correlation with NDVIc and NDCI. Then, by using a commercially available digital camera, which can take both visible and near infrared images, NDVIc and NDCI pseudo color images were visualized from the images obtained with appropriate optical filters. NDCI was proved better to be used for checking the degree of health in coral colonies in deeper water due to the high spectral sensitivity at the blue region of the camera.

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From August 2006 to December 2007, the concentrations of silicate (Si(OH)₄), phosphate (PO₄), and dissolved cadmium (Cd) were monitored in the surface water at three stations in the coastal zone off Miyara River, Ishigaki Island and the mouth of the Miyara River. The distances of offshore stations from the shoreline were approximately 1800, 2700, and 3900 m, respectively. From the results of the surface-water temperature and salinity, offshore sites were classified into three seasonal water mass groups, namely, from December to May, June to October, and November. From December to May, the surface-water temperature was relatively low, and the surface-water salinity was relatively high. On the other hand, from June to October, the water temperature increased, and the salinity scattered in a wide range towards the low salinity zone due to the influence of relatively large precipitation in this season. In November, the T-S diagram intermediated between those two groups. The concentrations of Si(OH)₄, PO₄, and Cd at the offshore sites were extremely small (the maximum concentrations observed were 7μM, 0.13μM, and 32 pM, respectively) and showed little seasonal variations, suggesting that the influences such as eutrophication and heavy metal pollution upon the adjacent coral reef ecosystem could not be recognized in the present day.

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[in Japanese]

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[in Japanese]

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