On the maintenance mechanisms of scleractinian coral community in a peripheral area.

与冲绳Sesoko岛的珊瑚群落(在珊瑚礁区域)相比。1)尽管海岸线很长，但适宜珊瑚生长的浅水区比珊瑚礁区要窄。然而，在阿马库萨的几个地区，珊瑚覆盖率有时达到75%，与冲绳没有太大差异。然而，在Amakusa产卵的总数量比冲绳少得多。2)可能是由于这个原因，阿马库萨的幼虫定居密度很低，只有Sesoko的1/10000。3)Echinmetra等食草动物的影响似乎是幼年珊瑚的一个明显的死亡因素。这种食草动物在Amakusa的密度比Sesoko低。因此，两个地区的差异相对缩小，Sesoko的幼年珊瑚密度是。只达到了阿马库萨的5倍。4)在生长季节，Sesoko的珊瑚生长速度是。是…的1.5倍比在阿马库萨更多。如果继续保持5倍的密度，预计Sesoko IS的覆盖率将迅速增加。然而，覆盖范围如此迅速的变化还没有报道。这一事实表明，一些强大的捕食者，如棘鸟和其他影响死亡的因素，导致了密度的下降。然而，这种降低密度的影响因素在阿马库萨相对较少。根据1990年用螳螂法进行的珊瑚分布普查，在阿马库萨很少有觅食的疤痕和部分死亡的群体。5)据报道，阿马库萨的大部分珊瑚在1962/63年冬季的严寒中死亡。在阿马库萨，桌型珊瑚的直径有时可达2米。如果本研究测量的直径为9毫米的年增长率持续30年，目前桌型珊瑚的最大尺寸与上述报告一致。这一事实表明，寒潮过后，阿马库萨的珊瑚在良好的条件下生长。孤立木的个体大小频率数据呈现出从小到大的连续格局。这种连续的大小结构表明年轻群体的不断定居。6)在没有强大捕食者的阿马库萨，有效的死亡因素似乎是冬季低温、夏季高温和台风季节的波浪作用。许多与珊瑚有关的钻孔虫似乎也是台风期间珊瑚减少的原因。较少

In comparison with the coral communities of Sesoko Island of Okinawa (in coral reef area). some features of the coral communities in Amakusa have been made clear.1) In spite of the long coast line, suitable shallow area for coral growth is narrower than that of coral reef area. However in several areas in Amakusa, coverages of corals sometimes reached 75%, and were not so much differed from that of Okinawa. However, total number of eggs spawned in Amakusa was quite fewer than in okinawa. 2) Presumably for this reason, density of larval settlement in Amakusa was quite low, only 1/10000 of Sesoko Is. 3) Effect of grazer such as Echinometra seemed as a distinct mortality factor of young corals. Density of this grazer is lower in Amakusa than Sesoko. Consequently, the discrepancy of both areas decreased relatively and the density of young corals in Sesoko Is. reached only 5 times of that in Amakusa. 4) During the growing season, the growth rate of corals in Sesoko Is. was 1.5 times higher … More than in amakusa. If the 5 times density is continuously maintained, rapid increment of coverage is expected in Sesoko Is. However, such rapid change in coverage have been not reported. This fact shows that some powerful predators such as Acanthaster and other influential mortality factors cause the reduction in the density. However, such influential factors lowering the density were raltively rare in Amakusa. According to the general survey on the distribution of corals by manta-method carried out in 1990, feeding scars and colonies partially died were rare in Amakusa. 5) It reported that most of corals in Amakusa died during the severe cold wave of 1962/63 winter. Diameter of table type corals, such as Acropora soliataryensis, sometimes reaches up to 2 m in Amakusa. If annual growth rate of 9 mm in diameter, measured in the present study, continues for 30 years, the maximum size of table type corals now present agree with the above report. This fact shows that scleractinian corals in Amakusa are growing under good conditions after the cold wave. Size frequency data of A. solitaryensis showed a successive pattern from small to large size. This successive size structure suggests a continuous settlement of young colonies. 6) In Amakusa where there is no powerful predator, effective mortality factors seem to be low temperature in winter, high temperature in summer and wave action during typhoon season. Many borers associated with corals also seems to contribute this reduction of corals during typhoon. Less