What process forms coral reefs?

• A. Sedimentation in rivers
• B. Erosion of shorelines
• C. Coral polyps settling on hard surfaces and building exoskeletons
• D. Melting polar ice

Answer: (C)

Coral reefs form when coral polyps settle on a hard surface and secrete calcium carbonate to build their tough exoskeletons. As colonies grow, new polyps bud from the originals, stacking up limestone to create the reef’s sturdy framework. In warm, shallow, sunlit waters, the tiny algae that live inside the coral also provide energy through photosynthesis, helping the reef grow. The other ideas describe processes that would bury, wear away, or change the environment rather than build the reef structure: sedimentation can smother corals, erosion breaks them down, and melting polar ice affects climate but doesn’t directly create reef form.