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喜欢科学,偏爱自然科学。也喜欢技术,儿时喜围观打锡壶的和锔盆锔锅的。当过工人,当过兵,第二故乡是湖南、广西和广东。

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海洋中的雨林——珊瑚  

2014-03-31 15:25:39|  分类: 环境与农业 |  标签: |举报 |字号 订阅

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(1)

珊瑚礁覆盖着世界海洋面积的不足千分之一,却支持着超过所有海洋生物的25%。它们是海洋中的“雨林”。不幸的是全世界的珊瑚礁都遇到了麻烦,比如说大堡礁在1985年到2012年间的27年中面积减少了一半。如果这种趋势继续下去的话,到2020年它将会丢失剩下来的面积的一半。大堡礁位于昆士兰州海岸外约2600千米,有2900多个礁和900多个岛。

这个巨大的结构是由数以万亿计的微小的动物——珊瑚虫建造而成。每一个珊瑚虫是一个圆筒形的动物,通常直径只有几毫米,长度仅有几厘米。它们座落在石头或先前珊瑚的残留物上,分泌碳酸盐的外骨骼作为它们的基础。

(00m23s)

Coral reefs cover less than one tenth of one percent of the area of the world’s oceans. But they support more than twenty-five percent of all the creatures that live in the oceans. They are the rainforests of the seas. Unfortunately coral reefs worldwide are in trouble. For example, the Great Barrier Reef has lost half of its coral cover in the twenty-seven years between nineteen eighty-five and two thousand and twelve. And if the trend continues it will lose half of what is left by the year twenty twenty-two. The Great Barrier Reef stretches some two thousand six hundred kilometers off the coast of Queensland with over two thousand nine hundred individual reefs and some nine hundred islands.

This enormous structure is made of and was build by trillions of tiny animals, animals known as coral polyps. Each polyp is a cylindrical animal usually only a few millimeters in diameter and a few centimeters long. They sit on rock or on the remains of previous coral and they excrete a carbonate exoskeleton as their base.

(2)

但是它们不能自己独立生存。它们与一种藻类生活在非常舒适的互惠互利的关系中,这种藻类就是动物黄藻,或更通俗的叫法是虫黄藻。它们的关系是如此之密切,虫黄藻实际上生活在它的宿主——珊瑚虫的肉体之中。珊瑚虫给它们二氧化碳和铵,而作为回报虫黄藻给予珊瑚虫必需的碳水化合物营养品,它们因此得以生长。的确,虫黄藻为它的宿主提供了超过95%的代谢需求。

虫黄藻确实很不可思议。与其他任何生命形式都不同,它们携带的DNA数量是我们人类的100倍,我们不知道为什么。它们也进行光合作用,不过其方式却与其他任何生命体都不同。它们还是珊瑚色彩的来源之一,因为它们天生带有棕黄色。

当珊瑚处于某种压力之下,比如不正常的高水温时,珊瑚虫会把它的朋友虫黄藻排出体外,这时珊瑚虫也就失去了它们的颜色,这种情形称为珊瑚白化。如果在几天之内它们不再引入虫黄藻的话,它们的幸福婚姻就此终结,珊瑚虫也就死亡了。世界范围的珊瑚白化在1970年代末开始发生,那是当大气二氧化碳水平达到约320ppm (百万分之)时出现的。

(01m38s)

But they cannot survive by themselves. They live in a very cosy mutually beneficial relationship with some microscopic algae known as zooxanthella, or more commonly as symbiodinium. The relationship is so close that the symbiodinium actually live inside the flesh of the host, coral polyp. The polyps give them carbon dioxide and ammonium, and in return the symbiodinium give the polyps essential carbohydrates in nutrients so that they can grow. Indeed, the symbiodinium provides more than ninety-five per cent of the metabolic needs of the coral polyps inside which they live.

The symbiodinium are really quite weird. And unlike any other life form they have one hundred times more DNA than we humans have. And we have no idea why. They do photosynthesis but by a completely different process from all other life harvesting organisms. They are also one of the sources of color of coral thanks to they inherent brown-yellow coloration.

When coral is under stress, for example, due to abnormally high temperatures in the water, the polyps actually expel their friends, symbiodinium, from their body. The polyps lose their coloration and this event is called coral bleaching. If they don’t take up some symbiodinium within a few days their happy marriage is doomed and the coral dies. Worldwide coral bleaching began happening in the late nineteen seventies, which is when atmospheric carbon dioxide levels reached around three hundred and twenty parts per million.

(3)

我前面说过近期研究显示大堡礁在27年间失去了它的一半珊瑚。其中约10%直接由珊瑚白化造成;约48%是风暴的损失;约42%是由声名狼藉的长棘海星(刺冠星鱼,棘冠海星)造成的。

毫无疑问,由于全球气候变暖升高了大气和海洋的温度,大气系统中拥有了更多的能量,预计未来风暴的损失会更多。而随着大堡礁周围环境的变化,长棘海星的数量也增加了,它们爬到珊瑚虫上,把自己的胃翻出来,把珊瑚虫的肉质液化并吸吮一空。

(03m25s)

Now as I said recent researches have shown that the Great Barrier Reef lost half of its coral in a twenty-seven year window. About ten percent of that was directly due to coral bleaching; about forty-eight per cent was caused by storm damage; about forty-two percent was due to attack by the infamous crown of thorns (or crown-of-thorns) starfish.

Certainly with global warming raising the temperature of both the atmosphere and the oceans, there is more energy in those systems and we would expect more storm damage. And as the environment along the Great Barrier Reef has changed the crown of thorns starfish has increased in numbers. They sit on top of the coral polyps turn their stomach inside out and then liquefy and absorb the flesh of the coral.

(4)

我们需要珊瑚礁。一方面,通过食物链它们是亚洲10多亿人的蛋白质的主要来源;另一方面,潜水旅游仅在加勒比海一地就产出达每年一千多亿美元;在澳大利亚,到大堡礁的国际旅游收入约为70亿美元每年。

不幸的是,珊瑚虫在对付急剧变化的环境方面完全不在行。它的生命周期很长,并且常常是通过克隆来进行无性繁殖,因而后代具有与父母完全相同的特性。有性繁殖的后代与父母是不同的,因而在对付变化方面的机会就多一些。

因此,如果珊瑚虫不能马上改变它们的生活方式,我们人类可能就不得不马上行动了。

——《卡尔博士的科学伟大时刻》/《目标2050:寻常堡礁?》,ABC 2014/3/19

(04m40s)

We need our coral reefs. On one hand they are a major source of protein for over one billion people in Asia via the food-chain. And on the other hand, diving tourism in the Caribbean along generates over one hundred billion dollars each year. In Australia the income from international tourism to the Great Barrier Reef is around seven billion dollars each year.

Unfortunately the coral polyp has exactly the wrong characteristics to deal with the rapidly changing environment. It has a very long life cycle and often reproduces asexually by cloning. So the babies have exactly the same properties of their parents. In sexual reproduction the babies are different from their parents and have a better chance of dealing with changes.

So if the coral polyps can’t change their ways in a hurry, maybe we have to.

-- Dr Karl’s Great Moments in Science / Destination 2050: the Mediocre Barrier Reef? ABC 2014/3/19

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