When so many oysters died off the coast of Britain that some native species were threatened with extinction, the fact...

on August 19 at 07:48PM

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Can someone please explain this question? Thanks!

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Irina on August 28 at 08:58PM

@Minerva,

The passage tells us that when oysters died off the coast of Britain, the rise in water temperature was thought to be the cause. Later, the cause was determined to be the chemical tributyltin, used to keep barnacles off the hulls of boats. TBT has been nearly eliminated the chemical from the British waters but the endangered oyster population has not grown.

The question asks us to resolve this paradox. The correct answer choice will likely state an alternative reason for why the native oyster population has failed to grow.

Let's look at the answer choices:

(A) The increase in water temperature has slowed in the years since the legislation was passed.

Incorrect. The water temperature is irrelevant since TBT was the true cause of oyster population decline.

(B) Native oysters rely on different sources of food than do the barnacles that live on the hulls of boats.

Incorrect. This fact would suggest that the oyster population should increase even assuming barnacle population has grown since the ban of TBT.

(C) TBT also killed imported varieties of oysters that flourish at the expense of native oysters.

Correct. Since imported oysters directly compete with native oysters, and imported oysters recovered after the ban of TBT, their growing presence explains the fact that the native oyster population has failed to grow.

(D) Other chemicals that are used to remove barnacles seem to have little effect on the oyster population.

Incorrect. If this fact is true, we would expect the oyster population to grow in the absence of any harmful chemicals.

(E) TBT is more deadly to oysters in colder waters than in warmer waters.

Incorrect. TBT is all but eliminated from the waters, and any small amounts that remain are less harmful now since the waters are warmer, thus we would expect the oyster population to recover if this were true.

Does this make sense?

Let me know if you have any further questions.