Official Solution:
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.
Which of the following, if true, most seriously undermines the researchers' reasoning?
A. Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
B. Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
C. In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
D. The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
E. If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.
The researchers conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs, based on the finding that scraped sections had fewer surviving eggs than undisturbed sections. The correct answer provides an alternative explanation for the experimental result that has nothing to do with algae's role in reproduction.
(A) Incorrect. If fish preferentially lay eggs on bare surfaces rather than algae-covered ones, removing algae should have made those sections more attractive for egg-laying - producing more eggs in the scraped sections, not fewer. This is inconsistent with the observed result and does not undermine the researchers' reasoning.
(B) Correct. The scraped sections were prepared by physically removing all algae from the reef surface. If scraping causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site, then the scraped sections may have had fewer surviving eggs not because algae was absent but because the scraping process directly damaged the surface. This alternative explanation undermines the conclusion that algae itself is responsible for the difference.
(C) Incorrect. If algae protects eggs from predators and strong currents, this would explain why undisturbed sections had more surviving eggs - supporting the researchers' conclusion rather than undermining it.
(D) Incorrect. Whether hatching rate is a better measure of reproductive success than egg survival is irrelevant here - the experiment measured egg survival and the conclusion is drawn from that data. Introducing a different metric does not affect the reasoning about algae's role.
(E) Incorrect. The potential for algae to eventually reduce oxygen availability is a long-term concern unrelated to the short-term egg survival measured in the experiment. It has no bearing on whether the experimental result was caused by algae's presence or absence.
Answer: B