Home > Corals

Updated 7/13/2023


Unattached disc, sandal-like, or conical, with
radiating ribs, unattached
Clumps with a few large polyps
Large tentacles hiding skeleton,
or lack thereof
Tables composed of many branches    
Solid plates with free edges
Branching / Digitate / Columnar
Massive / Hemispherical / Brain-like

There are several hundred species of reef-building corals around the world, 70 of which are known from Hawaii, in addition to many more in very deep water.  It can be difficult to identify some species with certainty, especially underwater, without examining the skeletal structure of the calices (cups inhabited by individual polyps).  Additional work is now conducted using genetic markers.  Hawaii's isolated location and subtropical water temperatures have led to the formation of several endemic species, variations within single species, and intergradations among others.  Most corals are colonies of thousands of polyps (clones) which form the familiar "coral head".  Exceptions include Mushroom or Razor Corals  which are typically a single animal.  Corals receive their distinctive colors from algae cells called zooxanthellae embedded within the animals' transparent flesh.  Oxygen and carbohydrates that zooxanthellae produce by photosynthesis are the principal source of energy for most corals, with zooplankton having little or no importance.  Cup Corals are an exception; lacking zooxanthellae, they feed upon large zooplankton at night.  Many species can be readily identified by color, but there are always exceptions.  Have a look at the photos for some common variations.

Corals may grow as little as 1/4 inch per year and are prone to damage by anchors, swimmers, and divers.  Take care to avoid touching live coral; their delicate flesh may be injured if pressed (even lightly) against the razor-sharp skeleton, allowing infection or algae to take hold, weakening and potentially killing the colony.  Since December 1998 it has been illegal to collect live corals or "live rock" at any time without a scientific collecting permit in Hawai'i: http://hawaii.gov/dlnr/dar/coral_liverock.html

All coral skeletons illustrated are from scientific collections taken prior to 1998.