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Commonly Asked Questions

Appears in Georgia Aquarium's:
  • Multiple exhibits (Tropical Diver)
General Information
  • Individual coral is called a polyp.
  • Coral polyps are invertebrate animals in the phylum Cnidaria and class Anthozoa.
  • Some species of coral remain a single polyp – others will reproduce and form colonies of identical polyps.
  • Colonies are composed of hundreds to hundreds of thousands of polyps.

Range / Habitat

  • Tropical corals generally require temperatures ranging from 73.4 to 84.2 Fahrenheit (23-29 C).
  • No deeper than approximately 230 feet (70 m) for sunlight, which is required for photosynthesis to occur.
  • Clear water with little sedimentation to allow for feeding and sunlight penetration.
  • Appear in reefs, though are not usually involved in reef-building. (An exception: Heliopora is an octocoral and a reefbuilder that builds a massive skeleton.)

Physical Characteristics

  • All species of soft coral have eight tentacles which provide defense, capture food and clean debris. They are part of the sub-class Octocorallia.
  • Nematocysts in tentacles release an often-fatal toxin into prey or threats.
  • Gorgonians have a protein-based skeleton composed of gorgonin or tightly clustered calcium carbonate spicules. Non-gorgonians have calcium carbonate spicules imbedded throughout their tissue
  • In some cases, polyps will specialize based on their physical position in the colony. For example, central polyps form a supporting structure.
  • Some soft corals do not have zooxanthellae in tissue. However, all species that we currently have represented at the Aquarium contain zooxanthellae.

Diet / Feeding

  • Stomach has one opening – the mouth. It is surrounded by tentacles that capture food. Food enters mouth and leaves mouth once it has been digested.
  • Feeds predominantly at night.
  • Polyp receives nutrients by:
    • Filtering food from water with its tentacles, capturing food by using stinging nematocysts.
    • Mutualistic zooxanthellae (single-celled algae) receive water and carbon dioxide from the polyp, photosynthesizing the latter into oxygen, carbohydrates and lipids.

Conservation Status

  • Varies on a per-species basis, but coral reefs in general face threats from pollution, climate change and other factors.
  • While oceans are absorbing and bearing a large brunt and absorbing excess carbon dioxide in the atmosphere (as much as 30% of the total), the result is acidification at an accelerated rate.
  • Corals are not adapted to the current, increased rate of ocean acidification and face long-term detrimental effects.

Additional Information

  • There are also deep-water/cold-water corals:
    • There are stony and black/horny varieties in deep water ranging to 6561 feet (2000 m).
    • Waters as cold as 39 Fahrenheit (4 C).
    • No zooxanthellae.