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Stony Corals (Hard Corals)

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Pillar Coral / Cmd William Harrigan, NOAA Photo Library

Pillar Coral

Commander William Harrigan, NOAA Corps (ret.), FL Keys National Marine Sanctuary, NOAA Photo Library
Stony corals, also called hard corals (as opposed to soft corals, like sea fans), are the reef-builders of the coral world. Learn more about stony corals - what they look like, how many species there are, and where they live.

Characteristics of Stony Corals:

Stony corals:

  • Secrete a skeleton made of limestone (calcium carbonate).
  • Have polyps that secrete a cup (calyx, or calice) in which they live, and in which it can withdraw for protection. These polyps usually have smooth, rather than feathery tentacles.
  • Are usually transparent. The brilliant colors associated with coral reefs are not caused by the corals themselves, but by an algae called zooxanthellae that lives within the coral polyps.
  • Are composed of two groups: the colonial corals, or reef-builders, and the solitary corals.

Stony Coral Classification:

  • Kingdom: Animalia
  • Phylum: Cnidaria
  • Class: Anthozoa
  • Order: Scleractinia

According to the World Register of Marine Species (WoRMS), there are over 3,000 species of stony corals.

Other Names for Stony Corals:

Stony corals are known by many different names:

  • Hard corals
  • Reef-building corals
  • Hexacorals
  • Hermatypic corals
  • Scleractinian corals

According to the World Register of Marine Species (WoRMS), there are over 3,000 species of stony corals.

Where Stony Corals Live:

Corals aren't always where you think they'd be. Sure, many of the reef-building corals are warm-water corals - restricted to tropical and subtropical areas where the water is salty, warm and clear. The corals actually grow faster when they have more access to sun. They can build large reefs like the Great Barrier Reef in warmer waters.

Then there are corals found in unexpected areas - coral reefs and solitary corals in the deep, dark sea, even as far down as 6,500 feet. These are the deep-water corals, and they can tolerate temperatures as low as 39 degrees F. They can be found around the world.

What Stony Corals Eat:

Most stony corals feed at night, extending their polyps and using their nematocysts to sting passing plankton or small fish, which they pass to their mouth. The prey is ingested, and any waste is expelled out the mouth.

Stony Coral Reproduction:

These corals can reproduce both sexually and asexually.

Sexual reproduction occurs either when sperm and eggs are released in a mass spawning event, or by brooding, when only sperm are released, and these are captured by female polyps with eggs. One the egg is fertilized, a larva is produced and eventually settles to the bottom. Sexual reproduction allows coral colonies to form in new places.

Asexual reproduction occurs through splitting, in which a polyp splits into two, or budding, when a new polyp grows out of the side of an existing polyp. Both methods result in the creation of genetically identical polyps - and the growth of a coral reef.

Asexual reproduction occurs through splitting, in which a polyp splits into two, or budding, when a new polyp grows out of the side of an existing polyp. Both methods result in the creation of genetically identical polyps - and the growth of a coral reef.

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