Question

Coral reefs provide crucial habitats, yet their extensive calcium carbonate skeletons create dense structures vulnerable to bioerosion by organisms like parrotfish and sponges, which can break down reef frameworks. However, researchers discovered that parrotfish grazing on algae within reef crevices also scrape away sediment, improving water flow and nutrient access for corals, while sponges, though eroding, also filter nutrients from water. At reef edges, parrotfish grazing can destabilize the structure, leading to fragmentation, suggesting that the grazing activity of parrotfish ______
Which choice most logically completes the text?
A) is always detrimental to the structural integrity of coral reefs.
B) has complex, contrasting impacts on reef health, benefiting corals in some areas while harming reef structure in others.
C) is more significant in shallow, high-light zones compared to deeper reef environments.
D) primarily functions to remove excess algae, with structural impacts being a secondary, minor effect.

Answer 1

B

The passage describes both beneficial effects (scraping sediment from crevices, improving flow and nutrient access) and harmful effects (destabilizing edges and causing fragmentation), so parrotfish grazing has complex, contrasting impacts.