Wildlife Fact Sheet

Hard Coral

Hexacorallia

Lifespan | Some can live for more than 4,000 years
Habitat | Shallow areas less than 150 feet deep
Range | Around the world, in tropical and subtropical waters
Preferred Food | From symbiotic algae called zooxanthellae, and sometimes from zooplankton that drift by

About

Hard corals are known for being the building blocks of colorful reefs in tropical waters around the world. Although they look like small plants, they’re made of tiny animals called coral polyps. Coral polyps are soft-bodied but secrete limestone skeletons for support. Coral reefs are formed when many polyps come together and build on one another. The result is a colony of polyps that act as one organism. Then, many colonies of different types of coral make up the coral reefs we know and love.

Coral polyps are actually see-through, and get their colorful hues from algae called zooxanthellae. Polyps and zooxanthellae have a symbiotic relationship, meaning both organisms benefit—coral polyps get food from the algae, and in exchange provide protection with their hard limestone skeletons. When corals get stressed out by pollution or high temperatures, they kick the zooxanthellae out. This is called coral bleaching and can kill the corals if it goes on for too long.

Did You Know?

Coral polyps’ hard calcium carbonate skeletons contain bands, like tree rings, that record environmental changes in temperature, water chemistry and water clarity. These records help scientists reconstruct what past ages were like before humans kept records.

Get Ocean Updates in Your Inbox

Sign up with your email and never miss an update.

This field is hidden when viewing the form
Name(Required)
By providing your email address, you consent to receive emails from Ocean Conservancy.
Terms & Conditions and Privacy Policy


This field is hidden when viewing the form
Email Opt-in: Selected(Required)

Fast Facts

  • Hard Coral
  • Hard Coral