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Narrator: Listen to part of a lecture in a Marine Biology class.
听一段海洋生物学课程。
Professor: We've been talking about the decline of coral reefs in tropical areas all over the world...um... how natural and man-made stresses are causing them to degrade, and in some cases, to die.
我们之前提到了世界各地热带区域中珊瑚礁的衰落......即自然和人为（造成的）压力是怎样造成珊瑚礁退化的，某些情况下，死亡。
So now let's focus on a specific example of a natural predator that can cause a lot of damage to coral reefs—the Crown of Thorns, or CoT starfish.
让我们注意一下珊瑚礁自然天敌的一个具体例子，这种天敌能对珊瑚礁造成巨大伤害——刺冠海星，或COT海星。
The Cot starfish is found on coral reefs in the tropical Pacific Ocean and it eats coral.
刺冠海星生活在太平洋的热带区域中的珊瑚礁里，而且以珊瑚为食。
Now, in small numbers, the starfish don't affect coral reefs dramatically.
数量较小时，海星不会对珊瑚礁产生重大影响。
But periodically, starfish population explodes.
但海星数量有周期性地暴增。
And when that happens, the reefs can become badly damaged or even destroyed, something we are trying very hard to prevent.
当这种事情发生的时候，珊瑚礁会严重受损，甚至毁于一旦，而这正是我们费尽心力要避免的。
For example, during the 1960s, there was an outbreak of CoT starfish in the Great Barrier Reef, off the east coast of Australia.
例如，在20世纪60年代，在澳大利亚东海岸的大堡礁，刺冠海星数量暴增。
Luckily, the CoT starfish population gradually declined on its own and the reefs recovered.
幸运的是，刺冠海星的数量渐渐地自发减少了，珊瑚礁恢复了。
But we were left wondering—what cause the population to increase so suddenly?
但我们感到不解——是什么造成了刺冠海星数量突然暴增？
Well, over the years, we've come up with a few hypotheses, all still hotly debated.
这些年来，我们都提出了好几种假说，人们仍然争论不休。
One hypothesis is that it's a natural phenomenon, that the starfish naturally undergo population fluctuations following particularly good spawning years.
一种假说认为，这是自然现象，在特别适合产卵的那几年，刺冠海星自然会经历种群数量的波动。
There are also several hypotheses that suggest some sort of human activities are partly responsible, like fishing.
还有一些假说认为，一些人类活动也要负一定责任，比如钓鱼。
There are fish and snails that eat starfish, particularly the giant triton snail, which is the main predator of the starfish.
有鱼和蜗牛以海星为食，特别是巨型法螺蜗牛，是海星的主要天敌。
These fish and snails have themselves experienced a decline in population because of overfishing by humans.
由于人类过度捕捞，这些鱼和蜗牛的种群数量随之减少。
So with a decline in starfish predators, the starfish population can increase.
所以，海星天敌数量减少，海星数量就会增加。
