Why are reefs found mostly in shallow, clear water?
Coral reefs are built by tiny animals called polyps, which secrete a hard skeleton of calcium carbonate. Over many generations the skeletons of dead polyps accumulate and form the structure of the reef. Reef-building corals live in partnership with microscopic algae that live inside their tissues. The algae use sunlight to make food and share it with the coral, which is why reefs are found mostly in shallow, clear water where sunlight can penetrate. This partnership is sensitive to temperature: if the water becomes too warm, the corals expel their algae and turn white, a process called bleaching. Although bleached corals can recover if conditions improve, prolonged stress can kill them. Because reefs shelter about a quarter of all marine species, their loss would have effects far beyond the coral itself.
Answer and explanation
Correct answer: D. The algae inside the coral need sunlight
- Step 1: The algae make food using sunlight. Step 2. Sunlight penetrates only shallow, clear water. Answer: the algae need sunlight. Why not the others: the passage gives no support for these reasons.
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More Academic Passages (Set 2) questions
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