本研究以東沙環礁潟湖區之珊瑚群聚為對象，探討珊瑚群聚空間分布的差異，並針對兩個假說進行驗證，第一是東、西邊海水溫度不同，第二是地點間深度的不同。為了驗證假說，以潟湖區內的塊礁 (Patch reef) 為調查、採樣的單位，分別為較淺、約1-3米深的礁頂 (reef top) 和較深、約10-15米深的礁底 (reef base)，並系統性的規劃東、西兩邊各五組塊礁，比較珊瑚的生長、小珊瑚、珊瑚生殖、珊瑚類型分布與覆蓋率、溫度及珊瑚病蟲害。潟湖區內的微孔珊瑚，在礁底的生長速率顯著的比礁頂高；在東邊的生長速率顯著的比西邊的高。平均而言，微孔珊瑚的生長率為每年0.9公分。小珊瑚一共記錄到了十科，但以菊珊瑚科 (61.6%)、蕈珊瑚科 (16.6%) 及微孔珊瑚科 (9.7%) 佔大多數；各調查點的小珊瑚密度在每平方公尺0.1-3.0株之間，礁底的小珊瑚密度顯著比礁頂為高，同時多樣性指數也是礁底較礁頂高；蕈珊瑚科群體直徑的比較則是有潟湖東邊顯著大於西邊的現象。珊瑚生殖的部分，於2009六月中在各地點採集了珊瑚樣本共五科，軟組織經解剖及組織切片並未發現生殖組織，很可能在採集時東沙珊瑚生殖季節剛過。珊瑚類型分布與活珊瑚的覆蓋率、死珊瑚覆蓋\\率及死珊瑚比例分析，針對十組塊礁，僅在死珊瑚覆蓋率一項發現環礁西邊顯著的比東邊大，其他以及礁頂與礁底之比較均無顯著差別。活珊瑚覆蓋\\率從0.3-46%，死珊瑚覆蓋率從8%-76%，死珊瑚比例從10%-100%。若將礁頂與礁底的資料合併，十個樣點內，樣點6、7、9、10主要是競爭型的形態群為主，屬於保育等級2；樣點1、2、3主要以耐壓型的形態群為主，屬於保育等級1。樣點4、5、8，屬於保育等級4，具有較高的珊瑚生長型多樣性。海水溫度在2009年六月中至九月中期間，礁頂平均有36%的時間超過30℃，而礁底只有13%；平均95%的時間，礁頂溫度比礁底高，差值約攝氏一度；潟湖區西邊水溫平均有29%時間超過30℃，東邊只有9%時間超過30℃。在整個調查過程中，除了五隻零星的棘冠海星，並沒有發現其他珊瑚病蟲害。本研究發現環礁內潟湖區的珊瑚群聚有明顯的水平及垂直空間變異，同時不同區域的水溫也有不同，高水溫區，如礁頂及潟湖區西邊，珊瑚生長狀況較差。針對兩個假說，東、西邊水溫及深度差異，兩者皆對東沙環礁潟湖區的珊瑚群聚分布有影響。

The purpose of this study is to investigate the factors that are responsible for the distribution of coral communities in the lagoon of the Dongsha Atoll. Previous surveys proposed that there was significant difference of coral cover between the east and west sides of the lagoon. Two hypotheses, seawater temperature and water depth, were proposed to explain the spatial variation of coral distribution. In addition, the growth rate of poritid corals, coral recruits, sexual reproduction, and the occurrence of coral predators and diseases were also studied. Ten patch reefs 5 on the west and 5 on the east sides in the lagoon were selected and the corals on reef tops (1-3 m) and deep reef bases (10-15 m) were investigated. The growth rates of poritid corals on reef tops were higher on reef bases than those on reef tops, and higher in eastern lagoon than those in western lagoon. On average, the growth rate is 0.9 cm/year. A total of 10 families of small corals were recorded in which Faviidae (61.6%), Fungiidae (16.6%) and Poritidae (9.7%) constituted the majority. Diversity index comparisons indicated that reef bases have higher diversities than reef tops. The densities of small corals, ranging between 0.1-3.0 ind./m2, are higher on reef bases than on reef tops. In fungiids, individuals in the eastern lagoon were larger than those in the western lagoon. Tissues of corals were sampled in June 2009 for examination of gonads. However, no reproductive tissues were found after decalcification and histology. The morphological classes, live-coral coverage, dead-coral coverage and dead-coral ratio among the comparisons of reef bases vs reef tops and western vs eastern lagoons, only dead-coral coverage was found to be higher in eastern than in western lagoon. The live-coral coverage was 0.3-46%, dead-coral coverage was 8%-76% and dead-coral ratio was 10%-100%. Among the 10 patch reefs, patch reefs 6, 7, 9 and 10 are represented by mostly K type competitors and belongs to Conservation Class 2, patch reefs 1, 2 and 3 are presented by mostly S type stress-tolerated corals and belongs to Conservation Class 1. The remaining 3 patch reefs 4, 5 and 8 belong to the highest Conservation Class 4 and are represented by diverse types of corals. The water temperature exceeded 30°C in 36% of the time at reef tops, and 13% of the time at reef bases, during the summer period, i.e., between June and September, 2009. And the water temperatures were found in 95% of the time to be ~ 1°C higher at reef tops than at reef bases. The water temperatures were also higher in the west than in the east of the lagoon that 29% of the time exceeded 30°C in the west and 9% in the east only. No coral diseases or pests were found that may pose a large-scale threat in the near future. The variations of coral fauna found among habitats in the lagoon are consistent with the temperature patterns, i.e., the higher the temperature the poorer the coral condition. To the two hypothesis, in the eastern or western lagoon and the different depth are the factors of coral distribution in the lagoon.

壹、前言 1
貳、材料與方法 5
參、結果 9
肆、討論 14
參考文獻 24

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