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Some corals are targeted by yet more deadly predators. Predators that can crawl in search of their victims.
有些珊瑚被更致命的掠食者当成目标。可以爬行找寻猎物的掠食者。
Crown of thorns starfish, poisonous, invincible eating machines. They also extrude their gut and digest coral wholesale.
棘冠海星，具有毒性的无敌掠食机器。它们也会吐出内脏，将珊瑚整个消化。
But some corals have help. Small crabs living within their branches resist these onslaughts and defend their home.
但有些珊瑚会得到帮助。住在分枝中的小螃蟹抗拒这些突击，保卫它们的家园。
From beneath they launch an attack on the vulnerable underside of the starfish.
它们从海星脆弱的底部发动攻击。
Even the crown of thorns will retreat from such a determined attack, and this coral is left unharmed.
即使棘冠海星也需从如此坚定的攻击中退出，而珊瑚则毫发无伤。
Humphead parrotfish -- nearly a metre and a half in length. Their jaws are so powerful they can bite through rock.
长达1.5公尺的巨头鹦鹉鱼。它们强而有力的嘴能咬破石头。
When they descend to feed the reef itself is under threat. They are indiscriminate feeders, taking both rock and coral alike in their quest for algae.
它们下沉觅食时，就连礁岩也受到威胁。它们无所不吃，为了摄食海藻，他们也能因此吃下岩石及珊瑚。
These fish play a large part in the erosion of the reef.
这些鱼必须为礁岩的腐蚀负极大责任。
The rock and coral they swallow emerges later as a fine sand. On a single reef they can produce tonnes of it every year.
它们吞下的岩石及珊瑚最后变成一堆细沙。它们每年可从单一礁岩中制造许多吨沙。
This soft sand forms the tropical beaches that we find so alluring.
这些细沙组成了令人着迷的热带海滩。
Over time the sand builds up to form an island, which is then colonised by animals and plants.
时间一久，这些沙组成一个小岛，成为动植物的繁衍聚落。
Trees take root, birds arrive.
树木生根，鸟来作伴。
The guano from thousands of terns which have chosen to nest here enriches the sandy soil, which then can support more plants.
成千上万的燕鸥选择在这里筑巢，它们所制造的粪便肥沃了沙土，好让更多植物能在此生长。
But these terns, like other seabirds, depend on the ocean for their food.
但这些燕鸥像其他海鸟一样，靠海中的食物维生。
