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Question

Difficulty: HardWeaken

Marine Biologist: Over the past decade, coral cover in the Pelican Shoals marine reserve expanded by 28 percent following the introduction of artificial calcium-carbonate reef structures. During the same period, nearby unmanaged reefs without these structures experienced a 12 percent decline in coral cover. Because artificial structures provide optimal substrate for coral larvae settlement and stabilization, the installation of these structures was clearly the primary cause of the coral recovery in Pelican Shoals.

Which of the following, if true, most seriously weakens the marine biologist's argument?

  1. A
    Surveys conducted by independent oceanographers revealed that coral cover on the unmanaged reefs actually remained stable rather than declining by 12 percent.
  2. B
    Laboratory trials demonstrate that coral larvae settle on artificial calcium-carbonate substrates at rates significantly higher than on the natural seabed substrates found in Pelican Shoals.
  3. Concurrent with the installation of the artificial structures, authorities enforced an exclusive ban on commercial fishing in Pelican Shoals, triggering a surge in parrotfish populations that graze away coral-suppressing macroalgae.Answer
  4. D
    Artificial calcium-carbonate structures deployed in deep-water oceanic zones never sustain any species of branching stony coral.
  5. E
    The operational cost required to transport and submerge artificial reef modules exceeded the original budget allocated by the marine conservation authority.

Answer

The statement showing that a concurrent fishing ban caused an increase in algae-eating fish that protect young coral.
The biologist concludes that artificial calcium-carbonate structures were the primary cause of coral recovery based solely on a correlation between their introduction and an increase in coral cover. The correct answer undermines this causal claim by introducing a significant confounding factor: a concurrent commercial fishing moratorium that boosted populations of algae-grazing parrotfish. Because macroalgae compete with and suffocate young corals, the surge in herbivorous fish offers a robust alternative explanation for the coral expansion in Pelican Shoals, casting substantial doubt on the claim that the artificial structures were the primary driver.

Step-by-Step Solution

1
Analyze the structure of the argument
Premises: Coral cover in Pelican Shoals increased by 28% after artificial structures were introduced, while unmanaged reefs declined by 12%. Artificial structures offer good substrate for larvae. Conclusion: The installation of artificial structures was the primary cause of coral recovery in Pelican Shoals.
Deconstructing the argument into premises and conclusion is essential for identifying the logical gap.
2
Identify the logical flaw and underlying causal assumption
The author commits a correlation-to-causation fallacy by assuming that because the coral recovery followed the deployment of artificial structures and did not happen in unmanaged reefs, no other confounding variables or simultaneous initiatives were responsible for the improvement.
Weaken questions targeting causal claims are most effectively undermined by providing an alternative cause or showing a confounding variable.
3
Evaluate the answer choices for an effective weakener
The statement detailing the concurrent fishing ban and subsequent surge in herbivorous parrotfish provides an independent, highly plausible alternative explanation for the coral rebound, directly undermining the claim that the physical structures were the primary cause.
Demonstrating that another major causal factor occurred simultaneously in the managed reserve breaks the exclusive attribution to the artificial structures.

Key Concept

Causal Reasoning and Alternative Explanations
Estimated Time:1m 45s
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Topics

Weaken

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