Atolls
From coraldigest
Atolls
Atolls are circular reefs formed around volcanoes. After the volcano has submerged, a ring of coral 1-20 miles in diameter is left. [1]
Characteristics and Corals
There are two sides to an atoll. The outer edge facing the ocean slopes steeply to the ocean floor. Here, calcareous algaes flourish. The seaward margin faces into the center of the circle and drops much more gently. Here, you may find coral spurs or sediment-filled canyons.[1]
Location
Atolls are much more prevalent in the Indo-Pacific than in the Caribbean because of the relative abundance of submarine volcanoes. The few that are exhibited in the Caribbean are surrounded by fire coral instead of algal ridges. [1]