Coral (Zoantharia)

Aggregate and Branching Corals (from Myrtle Beach, South Carolina)

Coral (Zoantharia)

Assorted corals

Encased Polyp

By Patricia B. Mitchell.

The stony or hard corals may exist as individual animals or as members of complex colonies. There are approximately 800 reef-forming species of coral. Coral is a word used for both the soft-bodied polyp and the stony “skeleton” (called a corallite or theca) which it builds. Most corals live at depths of less than 150 feet in tropical seas, though some species can survive as far north as Alaska.

The invertebrate creatures are approximately ¼-1 inch, cylinder-shaped coelenterates which attach themselves to hard surfaces. On the upper, unattached end of the cylinder is a hollow surrounded by a ring of stinging tentacles. This is the “mouth” of the polyp. The coral eats by stunning or killing tiny shellfish larvae or algae with its tentacles, and then drawing them to its mouth.

Coral reefs usually form in shallow, clear, tropical marine waters. A reef is composed of great numbers of deceased and living corals and associated Zooxanthellae (single-celled plants) which reside in the living polyp's tissues. The individual creatures live “shoulder-to-shoulder” or with walls which touch their neighbors' walls. The limestone (calcium carbonate) “houses” of the individual corals can make vast condominiums, like the Great Barrier Reef off the east coast of Australia.

Coral are often found on East Coast beaches, and in the ocean side of the Chesapeake Bay. (Coral which washes in to the beach has broken off the rock or other hard surface to which it was attached.)

As the name indicates, Star Coral “cups” or houses have a pretty star- or flower-like pattern. If the coral was just recently broken off, the pattern will be sharply etched, but if the coral has been battered about by the waves for a while, the cups will be rounded and the pattern less defined.

As many as thirty Star Corals may group together to form an aggregation. This grouping, which looks like a very low-profile blob, can spread five inches in diameter. The color of the lime formation varies from white to brown.

Another type of coral known to the Southeast coast is Ivory Bush Coral, a branching formation which may reach three feet in size. When alive, this coral is red-brown. When dead, it bleaches white.

Red Coral, Corallium rubrum, from the Mediterranean, and Black Coral, Antipathes, of the Pacific, are considered very desirable for use in making jewelry.

Corals, which are kin to Sea Whips, Sea Pansies, and Sea Anemones, reproduce by expelling larvae, which are microscopic zooplankton. These “babies” float around in the sea, maturing, and some eventually come to rest on a hard substrate suitable for habitation.

An interesting note: Once a year all the corals in the Great Barrier Reef spawn at the same time. This action is triggered by the full moon. They “see” the moon's faint blue light by means of a protein in their bodies.


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