Listen to part of lecture of a marine biology class.
And the sea is teeming with tiny organisms, but they don't get as much popular attention as say, whales.
Microsop alge Microscopic algae just aren't as exciting I suppose. And yet those organisms are the foundation of the bog bulk of the marine food chane chain. Without planton plankton wich is the global turn term for this tiny organisms, there would be no whales. planton plankton is found both fresh water and marine evironments. Again it's the term we use for any small organisms that total long float along with a the current, either because they're too small or weak to swim againsted against it, or because they don't have any compacity capacity at all to move by themselves.
Plants and plant-like
planton plankton are called fighto planton phytoplankton, while animals and animal-like planton plankton are called zooplanton zooplankton.
For over a century now researchers have been trying to solve the myster about
You see some species of
zooplanton zooplankton might greate migrate, um, not the way birth's birds do when the seasons change. But daily, in a phenomenon we call Dio Diel Vertical Migration or DVM. In their Dio DielVertical Migration, zooplanton zooplanktonswim up near the surface of the water during the night and swim down to deeper water during the day. Depending on the species and region, this can be a round trip of between 100 and 400 meters.
For a tiny microscopic organism, that's a huge distance! Remember now,
zooplanton zooplanktoncan't swim very well and DVM requires a lot of enery. So there must be an important benefit to this these daily up-and-down commuting. We're not exactly sure what this benefit is. Though there are several compelling theories.
I'll talk about them in a moment, but first I want to talk about what we do know or rather what we are pretty sure we know.
So researchers generally agree that the stimulus for
zooplanton zooplankton DVM is light. zooplanton zooplankton tend to swim away from sunlight into deep water where the sun's rays barely penetrate. At night, when the sun no longer in lulate sha illuminates shallower water, zooplanton zooplankton head back toward the surface.
Now why would light cause
zooplanton zooplankton to expend all that energy and my great migrate?
One popular theory is that
zooplanton zooplankton are hiding during the day from visual predators, um, those animals that hunt by sight. The darkness provides safety during the day.
They at night after migrating upward, they have an opportunity to feed on phytoplankton that float at the surface. Make sense, doesn't?
But what do we do with the data showing that many kinds of
zooplanton zooplankton don't dive deep enough during the day to become invisible to predators or that others dive deeper that it's necessary to escape hunter's eyes. And some zooplanton zooplankton are bioluminescent, which means they have special organs that light up and make them visible even at great depths.
Well, despite all these, we believe predator avoidance is a possible explanation because of studies done in fresh water lakes. It turns out there is a
??? correlation between the pre??? presence or absense absence of vertical migration and the presence or absense absence of fish that find their pray prey by sight.
But what are some other possible explanations?
Some researchers suggest that
zooplanton zooplankton my great migrate to avoid the sun's ultraviolet light.That would explain why some zooplanton zooplankton are found at such great depth. Visible light not penetrate very far down, but ultraviolet light can. And we know that some zooplanton zooplankton have special pigments that protect them from the damage ultraviolet light can cause.
That could be why some
zooplanton zooplankton are able to stay closer to the surface during daylight hours.
And there is a third theory.
Although it takes a lot of energy for the
zooplanton zooplankton to migrate, they conserve energy while floating in deeper colder water. So while they're not feeding, they are quietly digesting in cooler water.
zooplanton zooplankton consist of any number of different organisms. From microscopic worms to crab larvae to tiny fish, and they are found in a large range of marine habitats, cold water, warm water, shallow water, deep water.
So there my be different reasons for different species.
① 第一个理论认为是光线影响，zooplankton白天为了躲避捕食者，所以潜伏在deep water，到了晚上到水面来捕食phytoplankton
might greatemigrate 迁移（草，其实我是听成了my great) DioDiel 迪尔 (我不确定，可能写成dio也是对的）
- teeming 充斥
- tiny 微小的
- organism 生物
- tiny organism 微生物
- Microscopic algae 微观藻类
- plankton 浮游生物
- bulk 块
- term 学期
- global term 全球术语
- capacity 能力
- phytoplankton 浮游植物
- DVM 昼夜垂直移动
- compelling 引人注目的
- stimulus 刺激
- penetrate 穿透
- illuminates 照亮
- shallower 更浅
- predators 捕食者
- bioluminescent 生物发光
- organs 器官
- correlation 相关性
- prey 猎物
- ultraviolet light 紫外光线
- penetrate 穿透
- pigments 颜料
- conserve 养护（这里指浮游生物在deep water保存能量、或体力）
- digesting 消化
- crab larvae 蟹幼虫
- larvae 幼虫
- derive [obtain something from (a specified source)] (直接理解为“获得”也没任何问题）（但是要注意from specified source）
- imply 意味着、暗示 （在TOEFL试题Question里面，正常是指 “暗示、隐喻”，通常用法是 professor 指出了一个fact，然后这imply了什么？）
- a round trip 一套往返路程
- commuting 通勤 （这里特指浮游生物DVM的行为，就跟上班一样）
- illuminates shallower 照得更浅
- compelling theories 令人信服的理论
- expend 花费
- presence 在场
- presence or absence 出席或缺席
Why does the professor mention fish that live in freshwater lakes?
To point out that many aquatic species exhibit diel vertical migration
To give an example of a species of fish that feeds on bioluminescent zooplankton
To make a comparison between fish and zooplankton
√To support one of the theories explaining why zooplankton migrate