A simple and rapid quantification system for zooxanthellae released from corals or existing in environmental waters was developed. Real-time PCR with a primer set designed to amplify the nuclear 18S rRNA gene of any genetic clade of Symbiodinium was used with intercalating dye SYBR^® Green I to enable the low-cost, simple assay of Symbiodinium density in surrounding waters. With the combination of a simple DNA extraction method developed recently by another group that traps cells onto a filter, the utility of the qPCR system was tested by investigating both the diel release pattern of Symbiodinium from Acropora digitifera in an aquarium and the occurrence of cells in field waters. Results showed that the system was fast and could accurately monitor Symbiodinium densities released from coral, and could possibly be applied to the Symbiodinium occurring in the field water —an outcome that could never be matched by conventional microscopic counts.

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In order to investigate the potential effect of algicidal (algae-killing) bacteria on zooxanthellae, some bacterial strains having algicidal properties were isolated from a coral community in the south of Kochi Prefecture (Japan) and their effect on freshly isolated zooxanthellae from Acropora formosa and zooxanthellae in culture (CCMP 2466-Symbiodinium goreaui (Trench et Blank)) was observed. Out of twenty bacterial strains isolated, three strains (strain 4-2DW-1, strain 4-1SW-1 and strain 1B) were found to have strong algicidal activity towards zooxanthellae with considerable cell degradation in up to five different grades (transparent/bleached cells, shrunken cells, swollen cells, necrosis and degradation). In case of freshly isolated zooxanthellae, the algicidal activity of strains 1B, 4-2DW-1 and 4-1SW1 affected 64-86%, 48-67% and 56-75.4% of cells respectively. However, in case of cultured zooxanthellae CCMP 2466-Symbiodinium goreaui (Trench et Blank), only 8-11% of zooxanthellae cells were affected. The results of this study indicate the presence of algicidal bacteria in coral communities, which can influence the health condition of zooxanthellae and suggests that algicidal bacteria might be playing a role in bleaching of corals susceptible to bacterial attack.

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Acropora species richness was studied on the reefs surrounding Siladen Island in North Sulawesi, where a marine park was established in 1991. Direct observation was done at 8 stations, where each station comprised the three topographic reef zones: reef flat, reef crest and reef slope. 46 Acropora species were identified. Among all these species, only Acropora indonesia is endemic to Indonesia, while most of the other Acropora species have widespread Indo-Pacific distribution and a few (Acropora hoeksemai and A. brueggemanni) are limited to the central Indo-Pacific. Acropora palifera was the most wide distributed species, occurring at all the stations observed. 11 species were found on the reef slope that do not occur in the other zones. On the reef crest, the unique species are A. aspera, A. specifera and A. divaricata, while A. palmerae was the only unique representative of the reef flat. Although the composition of Acropora species in each reef zone was not statistically different, we found 38 Acropora species on the reef slope, 27 on the reef crest and 22 on the reef flat. The 46 Acropora species found in 3000 m² of habitat area corresponds to predicted data based on the relationship between Acropora species richness and habitat area. Several Acropora species were only found at a typical side of Siladen Island and were not found at other sides during this study.

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Temperature tolerances of the early development (up to 4-arm pluteus) of Echinometra mathaei were investigated at 16-34°C. The critical lower and higher temperatures for embryonic development were 16 and 34°C, respectively. At these two temperatures, 100% of the embryos showed abnormality within 48h after incubation. The lower and higher temperature for development of healthy embryos and larvae were 19°C and 31°C, respectively. The developmental times from the 2-cell to early larval stages showed significant differences among 19 to 31°C. At 19 and 31°C, the embryos reached in healthy 2-arm pluteus stage in 72 and 26h after incubation, respectively. The larval growth performance and relative growth ratios of the different organs of 4-arm larvae showed that they were able to tolerate a wide range of temperature without any abnormality. The present findings will be useful for elucidating the possible mechanisms of larval dispersal, as well as the distribution of this sea urchin in various marine locations worldwide.

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Many scleractinian corals exhibit intraspecific variation in color and colony morphology. Several color morphs of Galaxea fascicularis have been described in Okinawan populations. Colonies of G. fascicularis have also been divided into types based on the shape of tentacular microbasic p-mastigophore (MpM) nematocysts and the density of the coenosteum. To understand the relationships of color morphs and types based on various characters, we studied color pattern of polyps, shape of tentacular nematocysts, and density of the coenosteum of colonies of G. fascicularis collected at Sesoko Island, Zampa and Teniya, Okinawa. Colonies of G. fascicularis were divided into three morphotypes based on the shape of tentacular MpM nematocysts. In addition to two morphotypes S and H, which were previously reported to possess different types of MpMs, we found mixed-type colonies (morphotype M) whose tentacles possessed both types of nematocysts. Although the average size of skeletal vesicles of the coenosteum of morphotype S colonies was greater than that of morphotype H colonies, the size of skeletal vesicles varied largely among colonies belonging to the same morphotype and appeared to be affected by environmental factors. We could not find clear relationships between the color morphs and the morphotypes based on the shape of tentacular nematocysts in G. fascicularis.

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