What are large ridges of coral that develop along coastal edges and support various organisms called?

The term that accurately describes large ridges of coral that develop along coastal edges and support a diverse range of marine organisms is "coral reefs." Coral reefs are complex underwater ecosystems held together by calcium carbonate structures secreted by corals. These vibrant biological communities provide habitats for numerous species, making them one of the most productive and diverse ecosystems on Earth.

Coral reefs are formed in warm, shallow waters and play a crucial role in marine biodiversity, supporting everything from fish and invertebrates to algae and other organisms. They also protect shorelines from erosion and impact storm surges.

Other terms listed have distinct meanings: coral atolls refer specifically to ring-shaped reefs that encircle a lagoon, coral cays are small islands made of coral debris, and coral islands are broader and can include other land formations. However, none of these options encompass the broader range of ecosystems and structures represented by coral reefs. Thus, the best answer is indeed that they are called coral reefs.