英语听力：自然百科 澳大利亚大堡礁 Great Barrier Reef—17

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Far from killing them, cutting these animals in half actually creates two of them. They have to be physically³ picked off the reef or injected with poison to control their numbers. Today pollution levels have dropped and so has the Crown-of-throne's population, for now anyhow.

 

But there are worse things of the modern world that's doing to the reef. Even the smallest changing climate upsets the natural order here. The turtles are already feeling it. Their eggs are very heat-sensitive. With higher temperatures, fewer eggs are hatching. And the turtle population is in decline. In 40 years, there may be none left.

 

And the coral reef itself is in grave danger, because water temperature is a matter of life and death. A change of just one or two degrees can wipe it out.

 

The scientists are discovering that coral isn’t totally defenseless. It has a protection mechanism⁴ that defies belief. If temperatures get too hot, coral responds by trying to change the weather. It exudes⁵ an invisible chemical, the floats above the water, and encourages clouds to form, providing shade on the hottest days.

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