本篇文章共分 6 段，針對珊瑚的結構、珊瑚蟲的生長方式、珊瑚群的擴張原理以及變化成因做有系統的整理與說明。

本篇考題英文原文與對應之中文翻譯整理如下。練習作答解題時若有對語意不清楚之處，請仔細查閱對照，以提升閱讀理解能力。

What is Coral? 珊瑚是什麼？

1. 珊瑚的外觀結構

   Corals belong to a group of animals called cnidarians. This group encompasses hard and soft corals, sea fans, gorgonians, hydroids, jellyfish, and sea anemones. Although the group is remarkably diverse, there are a few features shared by all. They have a free-swimming larval stage and a simple body plan: a central mouth, through which material passes in and out of the body, and a ring of tentacles. The other distinguishing feature of the cnidarians is the presence of nematocysts (stinging cells), which are used to catch prey.

   珊瑚屬於一類被稱為刺胞動物的動物。這個群體包括硬珊瑚和軟珊瑚、海扇、柳珊瑚、水螅、水母和海葵。雖然這個群體非常多樣化，但有幾個共同的特點。它們有一個自由游動的幼蟲階段和一個簡單的身體結構：一個位於中央的嘴，物質通過它進出身體，還有一圈觸手。刺胞動物的另一個顯著特徵是存在線囊（刺胞），用來捕捉獵物。

2. 珊瑚蟲與珊瑚群

   Individual corals are known as coral polyps: each is a single animal. In isolation a coral polyp looks very similar to a sea anemone, but unlike sea anemones, which live separated from each other, corals form colonies. A few species remain solitary, but in most cases, new polyps bud off the initial founding polyp, and gradually colonies of thousands or even millions of polyps will grow, each connected to its neighbors by living tissue. Freed from the limitations of living alone, colonies can grow to immense sizes and live a very long time.

   單個珊瑚被稱為珊瑚蟲：每個珊瑚蟲都是一個單獨的動物。在孤立的情況下，珊瑚蟲看起來與海葵非常相似，但與海葵不同的是，海葵是彼此分開生活的，而珊瑚則形成群落。少數物種保持獨居狀態，但在大多數情況下，新的珊瑚蟲從最初的創始珊瑚蟲上發芽，漸漸地，由數千甚至數百萬個珊瑚蟲組成的珊瑚群將成長起來，每個珊瑚蟲都通過活組織與鄰居相連。擺脫了單獨生活的限制，珊瑚群可以發展到巨大的規模，並能存活很長時間。

3. 硬珊瑚與軟珊瑚

   Corals come in all shapes and sizes, but the basic plan is the same: polyps live as a surface layer on some sort of structure, be it hard and inflexible or rubbery. The hard, or true corals, for which reefs are most famous, build limestone skeletons beneath the living tissue. Soft corals, as their name implies, do not form solid skeletons; instead they secrete limestone crystal structures called sclerites, which are embedded within a jellylike matrix beneath the polyps. When they die, little is left of most soft corals as the limestone element of their makeup is so small and easily breaks up.

   珊瑚有各種形狀和大小，但基本結構是相同的：珊瑚蟲作為表面層生活在某種結構上，不管是堅硬和不靈活的還是有彈性的。珊瑚礁因其而出名的硬珊瑚，或稱真珊瑚，在活體組織下面建立石灰石骨架。軟珊瑚，顧名思義，不形成堅實的骨架；相反，它們分泌的石灰石晶體結構稱為硬石，嵌在珊瑚蟲下面的果凍狀基質中。當它們死亡時，大多數軟珊瑚幾乎沒有留下任何東西，因為它們構成中的石灰石元素非常小，很容易破碎。

4. 黑珊瑚

   By contrast, some sea whips and fans and, notably, the black corals, have such dense skeletons of limestone, protein, and minerals that they are highly durable and are collected and polished for jewelry. The skeleton of black corals is more dense the slower it grows, and it grows more slowly at depth. So it is the very deep, older colonies that are most highly prized.

   相比之下，一些海鞭和海扇，特別是黑珊瑚，具有非常密集的石灰石、蛋白質和礦物質骨架，因此非常耐久，而被採集和打磨成珠寶。黑珊瑚生長速度越慢，其骨架就越緊密，而且在深處生長得更慢。因此，位處深處，年代久遠的群落是最珍貴的。

5. 珊瑚的成長原理

   Coral reefs would not exist if it were not for the ability of coral polyps to secrete limestone or calcium carbonate. Sea water surrounding a coral is very rich in dissolved calcium carbonate, but the fluid inside the polyp cannot retain a large quantity of calcium carbonate, so it is laid down as microscopic needle-shaped crystals beneath and around the polyp. This process occurs in two stages. As the polyp expands to feed with its tentacles at night, it lifts off the skeleton, rather like a glove coming part way off a hand. At this stage, the calcium carbonate crystals form ridges. During the following day (when the coral polyp is retracted and lying on its new structure), the valleys between the ridges fill in with more calcium carbonate and the skeleton takes on a smoother appearance. Because the skeleton of hard corals is made of limestone or calcium carbonate, it is pure white.

   如果不是因為珊瑚蟲能夠分泌石灰石或碳酸鈣，珊瑚礁就不會存在。珊瑚周圍的海水含有非常豐富的溶解性碳酸鈣，但珊瑚蟲內部的液體無法保留大量的碳酸鈣，所以它以微小的針狀晶體的形式沉積在珊瑚蟲的下面和周圍。這一過程分兩個階段進行。當珊瑚蟲在夜間用觸角擴張進食時，它就會從骨架上抬起來，就像手套從手掌上脫落一樣。在這個階段，碳酸鈣晶體形成脊狀物。在第二天（當珊瑚蟲縮回並躺在其新的結構上時），脊之間的山谷被更多的碳酸鈣填滿，骨架呈現出更平滑的外觀。因為硬珊瑚的骨架是由石灰石或碳酸鈣製成的，所以它是純白色的。

6. 珊瑚成長的變化因素

   Each coral species lays down its skeleton in a different way. This gives rise to the extraordinary range of shapes and forms that hard corals take. Some form large boulders, where the polyps live in small, isolated depressions or grooves in the skeleton. Some grow in branches, which can be small and stubby, while others are spreading, treelike structures. Still others grow delicate, leaflike plates or flat tables. The range is huge, and to complicate the matter further, the same species will grow in a different way depending on the physical characteristics of the place in which it finds itself. Although a coral's genetic blueprint is fundamental in determining what it looks like, its appearance is also affected by waves, currents, light, and competition for space on the reef. Such variations in coral form have complicated the matter of identification over the years.

   每個珊瑚物種以不同的方式鋪設其骨架。這就產生了硬珊瑚所具有的非凡的形狀和形式。有些形成大石塊，其中的珊瑚蟲生活在骨架上的小而孤立的凹陷或凹槽中。有些生長在樹枝上，可能是小而粗壯的，而其他的則是平展的、樹狀的結構。還有一些生長在精緻的、像葉子一樣的板塊或平板上。分布範圍巨大，而且使情況進一步複雜的是，取決於其所在之處的物理特徵，同一物種將以不同的方式生長。儘管珊瑚的基因藍圖是決定它長成什麼樣子的基本因素，但它的外觀也受到波浪、水流、光線和對珊瑚礁空間的競爭的影響。多年來，珊瑚形態的這種變化使識別問題變得複雜。