IELTS Listening Part 4: a biology lecture on how sea otters protect kelp forests, and what happened when they almost disappeared.
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Names in this sentence:Part Four
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Part Four. You will hear a lecture about sea otters and kelp forests.
You have some time to look at questions thirty-one to forty.
Now listen carefully and answer questions thirty-one to forty.
Good afternoon. Today's lecture is about one of my favourite animals, the sea otter.
Yes, they're adorable. But they're also surprisingly important!
Sea otters live along the coasts of the North Pacific.
They spend almost their whole lives in the water, often floating on their backs.
They even hold hands while they sleep, so they don't drift apart!
Their home is the kelp forest, an underwater forest of giant seaweed.
Kelp can grow up to half a metre in a single day.
So why do otters matter so much to these forests?
The answer is sea urchins.
Urchins eat kelp, and without predators, their numbers explode.
Whole forests can disappear, leaving what scientists call urchin barrens.
Sadly, in the eighteenth and nineteenth centuries, otters were hunted for their fur.
By 1911, only around two thousand were left in the world.
And as the otters vanished, so did many kelp forests.
Fortunately, hunting was banned, and the otters slowly returned.
And wherever they came back, the kelp forests recovered too!
This is why ecologists call the sea otter a keystone species.
A keystone species has a huge effect on its environment, compared to its numbers.
Remove it, and the whole system can collapse.
Next time, we'll ask whether wolves played a similar role in Yellowstone.
Right, that's all for today. Thank you!
That is the end of Part Four.
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