Question 2·200 Super-Hard SAT Reading Questions·Information and Ideas
Marine ecologists have often treated greater coral-larval settlement near speakers broadcasting healthy-reef sounds as evidence that larvae swim toward such sounds. To separate movement toward a source from the decision to settle, Nia Patel and colleagues placed speakers playing either healthy-reef recordings or acoustically matched artificial sounds beside settlement tiles. They also installed fine-mesh traps a short distance from each speaker; the traps intercepted larvae carried into the area before those larvae could touch a tile. Although similar numbers of larvae entered traps in the two sound treatments, substantially more settled on tiles near healthy-reef recordings. In laboratory channels, moreover, larvae exposed to healthy-reef sounds began repeatedly contacting the channel floor sooner than did larvae exposed to artificial sounds, but neither group moved preferentially toward its speaker. Taken together, these results suggest that _____.
Which choice most logically completes the text?
For an inference question involving an experiment, identify what each measurement actually tests before interpreting the results. Here, trap counts measure arrival, directional movement measures navigation, and tile settlement and floor contact measure settlement-related behavior. The best inference must account for all these findings without claiming a mechanism that the researchers did not observe.
Hints
Separate two possible effects
Consider the difference between a sound causing larvae to enter an area and a sound changing their behavior after they have arrived.
Combine all three measurements
Compare the trap counts, the settlement-tile counts, and the direction and timing of movement in the laboratory channels.
Step-by-step Explanation
Distinguish arrival from settlement
The traps measured how many larvae entered the area before contacting a tile. Because the two treatments produced similar trap counts, healthy-reef sounds did not appear to increase larval arrival.
Evaluate the navigation claim
In the laboratory channels, neither group moved preferentially toward its speaker. This result provides no evidence that larvae used healthy-reef sounds to navigate toward a source, even at close range.
Identify the supported effect
More larvae settled near healthy-reef recordings, and larvae hearing those recordings contacted the channel floor sooner. Together, these findings support the inference that the sounds affected when nearby larvae began investigating surfaces rather than how they reached the area.