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Coming up next on Jonathan Bird's Blue World, a look alien invaders from other parts of the world.
接下来请收看乔纳森·伯德的《蓝色世界》，来看一种来自地球其他地方的外来入侵生物。
Hi, I'm Jonathan Bird and welcome to my world!
嗨，我是乔纳森·伯德，欢迎来到我的世界！
An ecosystem is a community of organisms living together in balance with each other.
生态系统是一个有机体群落，它们生活在一起，彼此之间获得一种平衡。
In theory, a balanced ecosystem will stay balanced and healthy as long as nothing disrupts the harmony of the inter-relationships between all the organisms.
从理论上讲，只要没有任何东西破坏所有有机体之间相互关系的和谐，一个平衡的生态系统将保持平衡和健康。
Many things can throw the balance of an ecosystem out of whack.
很多事情都会破坏生态系统的平衡。
For example, overfishing can remove certain animals from a reef ecosystem, creating a gap in the food chain that causes the whole ecosystem to suffer.
例如，过度捕捞会使某些动物离开珊瑚礁生态系统，在食物链上造成一个缺口，导致整个生态系统遭受损失。
But another, increasingly common, disruption of ecosystems comes in the form of invasive species.
但另一种越来越普遍的破坏生态系统的形式是物种入侵。
An invasive species is an organism that has been introduced into a ecosystem from somewhere else, often causing a change in the balance of that ecosystem.
入侵的物种是从其他地方引入生态系统的有机体，经常导致生态系统的平衡发生改变
Perhaps one of the most well-known invasive species in North America is the Zebra mussel.
也许北美最著名的入侵物种之一是斑马贻贝。
This harmless-looking mollusk lives in fresh water.
这种看起来无害的软体动物生活在淡水中。
They call them Zebra Mussels because of the Zebra-like pattern on the shell.
之所以叫它们斑马贻贝，是因为它们贝壳上有斑马的图案。
The Zebra Mussel has invaded the Great Lakes, St. Lawrence River, and numerous smaller lakes and ponds around the United States and Canada.
斑马贻贝已经入侵了大湖区、圣劳伦斯河，以及美国和加拿大周围许多较小的湖泊和池塘。
It was brought from Europe as larvae in the ballast water of ships.
它是作为幼虫从欧洲带到船舶压载水中的。
When a cargo ship travels with a proper load, it settles down into the water to the depth for which it was designed.
当一艘货船装载着适量的负荷航行时，它会沉到所设计的深度。
But sometimes on the return journey, there isn't enough cargo and the ship floats too high in the water, which isn't safe.
但有时在返程途中，货物不够，船在水中浮得过高，这样很不安全。
So the ship has tanks called ballast tanks, which are filled with water to weigh the ship down.
所以，船上有一个叫做压载水舱的舱，里面装满了水来给船增加重量。
When the ship arrives at its destination, the ballast tanks are emptied.
当船到达目的地时，压载水舱被清空。
Sometimes the water carries tiny planktonic invaders from another country, which are inadvertently released into the environment.
有时，水舱中的水会携带着来自另一个国家的微小浮游入侵生物，这些入侵生物会在不经意间被释放到环境中。
Since cargo ships go up and down the St. Lawrence on their way from all over the world to the Great lakes, ballast tanks are a big issue.
由于货船从世界各地驶到大湖区，途中在圣劳伦斯河中行驶，压载水舱成为一个大问题。
The zebra mussel was first detected in the Great Lakes in 1988.
斑马贻贝于1988年首次在大湖区中被发现。
Because it reproduces so quickly, within only a few years, everything in the Great Lakes was soon covered in a layer of zebra mussels.
因为它繁殖非常迅速，短短几年内，大湖区中的所有东西很快都覆盖上了一层斑马贻贝。
While the zebra mussel might not seem like much of a threat,
虽然斑马贻贝看起来并不具有威胁性，
they grow so densely that they clog the water intakes of hydro-electric power facilities, the hulls of boats and ships, docks and buoys.
但它们生长得如此密集，以至于堵塞了水电设施的取水口、船只的船体、码头和浮标。
It's estimated that the annual cost to control them in the Great Lakes exceeds 100 million dollars a year!
据估计，每年大湖区中用于控制它们的费用超过1亿美元！
Having never seen a zebra mussel, I head up to Clayton New York, to visit the beautiful thousand island region of the St. Lawrence river.
由于从未见过斑马贻贝，我前往纽约克莱顿，参观美丽的圣劳伦斯河的千岛区。
I join David Doubilet, the famous National Geographic photographer on a shore dive in the river to check out the mussels.
我和著名的国家地理摄影师大卫·杜比莱一起，我们在河岸边潜水，观赏贻贝。
David lives nearby, and this is practically his back yard.
大卫住在附近，这里几乎是他的后院。
We're diving an old wooden-hulled shipwreck called the Islander right near shore.
我们正在一艘名叫“岛民”的旧木体结构的沉船附近潜水。
As soon as I sink beneath the waves, I see zebra mussels attached to the wreck and the rocks on the bottom.
我一潜到浪下，就看到斑马贻贝附着在沉船和底部的岩石上。
Zebra mussels haven't been all bad, at least from a diving point of view.
斑马贻贝并不是一点好处也没有，至少从潜水的角度来看是这样的。
Because they eat by filtering plankton from the water,
因为斑马贻贝靠过滤水中的浮游生物进食，
Zebra mussels have massively improved the underwater visibility in the river and the Great lakes by removing so much of the plankton that clouds the water.
所以它们通过去除大量的浮游生物而大大提高了河流和大湖区的水下能见度。
