Coral reefs come in three main types — fringing, barrier and atoll — and the difference between them comes down to their relationship with land: how close they sit to it, and whether the land is still there at all.
Schools of pennantfish, pyramid butterflyfish and milletseed butterflyfish on an atoll reef in the Northwestern Hawaiian Islands. Credit: NOAA.
The three types
| Type | How it forms | Its shape |
|---|---|---|
| Fringing reef | grows seaward directly from the shore — the most common type | a border along the shoreline and around islands |
| Barrier reef | borders a shoreline like a fringing reef, but is separated from land by an expanse of water | a lagoon of open, often deep water between reef and shore |
| Atoll | a fringing reef that keeps growing upward after its volcanic island has sunk entirely below sea level | usually circular or oval, with an open lagoon in the center |
Why reefs matter
Coral reefs bring billions of dollars into the economy through tourism, protect coastal homes from storms, support promising medical treatments and are home to millions of aquatic species.
Protecting them
NOAA's Coral Reef Conservation Program protects reefs through research, education and preservation. Many reefs, such as the Virgin Islands Coral Reef National Monument, are part of NOAA's system of marine protected areas.
Sources
Based on "What are the three main types of coral reefs?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from oceanservice.noaa.gov
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