Why do reefs form in lines parallel to the shore rather than in deep water?

Reefs form in lines parallel to the shore primarily because they require shallow, warm, and sunlight-rich waters to thrive. This environment is typically found in coastal areas where the water is not too deep, allowing light to penetrate for photosynthesis by symbiotic algae living within coral tissues. Additionally, the proximity to land provides nutrients and sediment that can support reef growth while protecting the reef from strong oceanic currents found in deeper waters.