The most common type of coral reef which forms lagoons.

The most common type of coral reef that forms lagoons is the atoll.

Step 1: Understanding Coral Reefs Coral reefs are underwater structures made from calcium carbonate secreted by corals. Corals are colonies of tiny living animals found in marine waters that contain few nutrients.

Step 2: Types of Coral Reefs There are three types of coral reefs: fringing reefs, barrier reefs, and atolls.

Step 3: Atolls Atolls are often circular or oval in shape, with a central lagoon. Atolls are usually located in the middle of the sea and, as such, do not have a land mass in the center.

Step 4: Formation of Atolls Atolls are formed from the subsidence of volcanic islands. As the island and ocean floor subside, coral growth continues, keeping the reef at or near the sea surface. Eventually, the island subsides below the sea surface, leaving a ring of growing coral with an open lagoon in the center.

So, the most common type of coral reef that forms lagoons is the atoll.