An annular coral reef is a unique type of coral reef that is circular or ring-shaped in structure. Some synonyms for this term include circular coral reef, ring-shaped reef, and circular atoll. Another synonym for this type of reef is "atoll," which refers specifically to a ring-shaped reef with a lagoon in the center. Other descriptive phrases for annular coral reefs include "ring-shaped coral ecosystem" or "circular marine habitat." Regardless of the term used, annular coral reefs are important ecological systems that provide habitats for countless marine species and help protect coastlines from erosion and storm damage.