【英语时差8，16】垂直迁移

 Imagine if the only way for you to eat were to trek¹ twenty-five miles on foot to a restaurant and then trek all the way back home afterwards.   Imagine that this restaurant is a buffet², so you can't carry anything home in a doggie bag--you carry only what you can pack into your stomach. You burn so much energy making this trip that you have to make the same trek every single day of your life or else you starve. How well would you fare if this were your life?

For many of the ocean's smallest creatures, a meal is a very long journey away--all the way to the surface waters of the ocean. Millions of deep-sea creatures, such as krill, survive on plant material called phytoplankton. Because plants require sunlight in order to live, they're absent deep in the ocean where the light of day never reaches.

Yet the darkness of the deep is precisely³ why so many of the ocean's smallest creatures make it their home. It's safer down there where there isn't any light to make them visible to their predators⁴.

So these animals have to travel from the ocean's depths toward its upper layers to feast on the phytoplankton growing there. We call this the vertical⁵ migration⁶. Among these migrators are creatures so tiny we can't see them without a microscope. Larger migrators include the shrimp-like krill, animals that resemble small shell-less snails⁷ and jellyfish, and other fascinating creatures.

Not only do they have to make their journey quickly before the sun returns and exposes them as potential meals to larger animals, but they make this journey night after night after night.  

1 trek   

vi.作长途艰辛的旅行；n.长途艰苦的旅行

参考例句：

• We often go pony-trek in the summer.夏季我们经常骑马旅行。
• It took us the whole day to trek across the rocky terrain.我们花了一整天的时间艰难地穿过那片遍布岩石的地带。

2 buffet   

n.自助餐；饮食柜台；餐台

参考例句：

• Are you having a sit-down meal or a buffet at the wedding?你想在婚礼中摆桌宴还是搞自助餐？
• Could you tell me what specialties you have for the buffet?你能告诉我你们的自助餐有什么特色菜吗？

3 precisely   

adv.恰好，正好，精确地，细致地

参考例句：

• It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
• The man adjusted very precisely.那个人调得很准。

4 predators   

n.食肉动物( predator的名词复数 )；奴役他人者（尤指在财务或性关系方面）

参考例句：

• birds and their earthbound predators 鸟和地面上捕食它们的动物
• The eyes of predators are highly sensitive to the slightest movement. 捕食性动物的眼睛能感觉到最细小的动静。 来自《简明英汉词典》

5 vertical   

adj.垂直的，顶点的，纵向的；n.垂直物，垂直的位置

参考例句：

• The northern side of the mountain is almost vertical.这座山的北坡几乎是垂直的。
• Vertical air motions are not measured by this system.垂直气流的运动不用这种系统来测量。

6 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。

7 snails   

n.蜗牛；迟钝的人；蜗牛( snail的名词复数 )

参考例句：

• I think I'll try the snails for lunch—I'm feeling adventurous today. 我想我午餐要尝一下蜗牛——我今天很想冒险。 来自《简明英汉词典》
• Most snails have shells on their backs. 大多数蜗牛背上有壳。 来自《简明英汉词典》