Narrator: Listen to part of a lecture in a Marine Biology class.

旁白：听一段海洋生物学的演讲。

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.

教授：我们讨论了在世界各地热带地区珊瑚礁的数量的下降，额……大自然和人为压力是怎么使他们退化的，在有些情况下，死掉。

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.

现在让我们着眼于会对珊瑚礁产生很多危害的一种捕食者——棘冠星鱼，或者说CoT海星。

The Cot starfish is found on coral reefs in the tropical Pacific Ocean and it eats coral.

在热带太平洋的珊瑚礁上，可以发现CoT海星，它食用珊瑚。

Now, in small numbers, the starfish don't affect coral reefs dramatically.

数量不多的情况下，海星并不会严重地影响到珊瑚礁。

But periodically, starfish population explodes.

但是周期性的，海星的数量会激增。

And when that happens, the reefs can become badly damaged or even destroyed, something we are trying very hard to prevent.

当那个发生的时候，礁石会被严重地损害或者破坏，这是我们想尽力去阻止的。

For example, during the 1960s, there was an outbreak of CoT starfish in the Great Barrier Reef, off the east coast of Australia.

比如，在二十世纪60年代，在澳大利亚东海岸的大堡礁，CoT海星激增了。

Luckily, the CoT starfish population gradually declined on its own and the reefs recovered.

幸运的是，CoT海星的数量渐渐地下降了，并且礁石也恢复了。

But we were left wondering – what cause the population to increase so suddenly?

但是，我们想知道——是什么使得数量突然增加的？

Well, over the years, we've come up with a few hypotheses.

经过许多年，我们有了一些假设。

All still hotly debated.

所有的都有争议。

One hypothesis is that it's a natural phenomenon, that the starfish naturally undergo population fluctuations following particularly good spawning years.

一种假设就是：这是一种自然现象，在经历非常好的产卵年的时候，海星很自然地经历了数量的波动。

There are also several hypotheses that suggest some sort of human activities are partly responsible, like fishing.

也有一些假设说人类的一些活动负有一部分的责任，比如渔业。

There are fish and snails that eat starfish, particularly the giant triton snail, which is the main predator of the starfish.

有一些鱼和腹足类动物是吃海星的，尤其是那些大的法螺，他们是海星最主要的捕食者。

These fish and snails have themselves experienced a decline in population because of overfishing by humans.

这些鱼类和腹足类由于人类的过度捕捞，数量减少。

So with a decline in starfish predators, the starfish population can increase.

所以随着海星捕食者的数量减少，海星的数量增加了。

Another hypothesized human-related cause is fertilizer runoff.

另外一个被假定的和人类相关的原因是肥料的流出。

People use fertilizer for their crops and plants and a lot of it eventually makes its way from land into the seas.

人们对农作物和植物施肥，并且其中很多的肥料会达到海洋。

It's fertilizer, so it has a lot of nutrients.

这是肥料，所以它有很多营养成分。

These nutrients have an effect on the starfish, because they cause an increase in the growth of phytoplankton.

这些营养成分对海星有影响，因为他们使得浮游植物的生长增加了。

Phytoplankton are microscopic plants that grow in the ocean.

浮游植物是那些在海里生长的微小的植物。

Larval CoT starfish eat phytoplankton in their first month of life, so more fertilizer in the ocean means more phytoplankton, which means more starfish, bad for the reefs.

幼小的CoT海星在他们生命的第一个月是吃浮游植物的。所以海洋里化肥越多也就意味着浮游植物越多，而海星也会越多，这个对礁石是不利的。

Now, the final hypothesis has to do with storm events.

最后一个假设是关于暴风事件。

If some reefs are destroyed by storms, starfish populations that inhabited those reefs would have to condense and concentrate on the reefs that are left.

如果一些礁石被暴风破坏，在这些礁石上栖息的海星群体就会密集地聚集在在还尚存的礁石上。

So this can cause a kind of mass feeding frenzy.

这也会引起某种大量地的疯狂喂食。

So we have ideas, but no real answer.

所以说我们有想法，但是没有真正的答案。

And because we aren't sure of the causes for starfish population increases, it's difficult to prevent them.

因为我们不是很确定到底是什么引起海星数量增加的，要防止它就很困难了。

I mean, some progress has been made.

我的意思是，还是有一些进展的。

For example, new survey techniques have enabled us to detect population increases when the starfish are quite young, so we can be ready for them.

比如，新的研究技术使得我们可以在海星还很小的时候，就侦测到数量的增加，这样我们就可以为此做好准备。

But meaningful progress requires much better evidence about the cause.

但是更有意义的进展还需要更多关于原因的证据。

On the bright side, in all the research being done on causes, we have discovered something related to how starfish populations might affect coral reef diversity.

从好的一面来看，在所有关于原因的研究中，我们已经发现了一些关于海星数量可能怎么影响珊瑚礁的多样性的。

We think that when reefs are damaged, after a few years, the fastest-growing corals repopulate the areas.

我们认为，当礁石被破坏了，过一些年以后，最快速增长的珊瑚会重新注入这个地区。

And these fast-growing species can grow over the slower-growing species of coral, denying them light and preventing them from recovery.

并且这些快速增长的物种的生长会超过慢速生长的珊瑚，使得他们无法获得修复所需的阳光。

However, the faster-growing species are the preferred food of the CoT starfish.

然而，快速生长的种类是CoT海星偏爱的食物。

So when an outbreak of CoT starfish occurs, they thin out the fast-growing coral and may give the slower ones a chance to reestablish.

所以，当CoT海星数量增长的时候，他们会削减快速增长的珊瑚的数量，并且给那些慢速增长的珊瑚以恢复的机会。

So without the outbreak, the diversity of coral would be reduced.

所以，如果没有数量的激增，珊瑚的多样性就会减少。