定量PCR (real-time PCR) 手法を応用し, 環境水中に存在する褐虫藻の定量を可能にするシステムを開発した. 全クレードのSymbiodinium の核18S rRNA遺伝子をターゲットとするPCRプライマーと, SYBR^® Green Iを用いたインターカーレーター法により, 安価で簡単・迅速なアッセイシステムを構築した. フィルター上にトラップしたSymbiodinium 細胞からの簡便なDNA抽出方法とのコンビネーションにより, 水槽で飼育したAcropora digitifera によるSymbiodinium 細胞排出の日周性や, 天然海水中に出現するSymbiodinium 細胞の定量を試みた. Symbiodinium は細胞が小さく, 形態的な特徴に乏しいために, 従来の顕微鏡観察ではその同定・計数がほぼ不可能であったが, 上記の定量PCR法により, 環境水中のSymbiodinium 細胞の出現密度が簡便にモニターでき, また, その応用によって新たな知見が得られることが期待された.

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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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イシサンゴには色彩や群体型に種内変異を示すものが多い。沖縄のアザミサンゴでは数種の色彩変異型が報告されている。アザミサンゴは、触手のmicrobasic p-mastigophore (MpM) 型刺胞の形や共骨の密度によっても種内変異型に分けられている。色彩変異型や上記の形質に基づく変異型を詳しく記載し、それらの間の関係を調べることを目的とし、沖縄の瀬底島、残波、天仁屋の3カ所から採集されたアザミサンゴの色彩パターン、触手の刺胞の形態、共骨密度を調べた。アザミサンゴは触手の刺胞形態により3タイプに分類された。異なる形態のMpMを有する2タイプ (S, H) に加え、今回両タイプのMpMを有する群体 (タイプM) を発見した。タイプSの群体の共骨はタイプHより大きな泡状構造を有するため共骨密度は低いが、泡状構造の大きさはタイプ内でも大きく変異し、光強度などの環境により影響されると考えられた。刺胞形態に基づくタイプと色彩型の明確な対応は観察されなかった。

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