Corals, related to jellyfish, are soft, tubular polyps with a crown of tentacles used to grab plankton from the water. The most familiar are the hard corals of tropical reefs: colonies of tiny polyps in elaborate skeletons made of calcium carbonate. Off the Georgia coast, though, the common corals are soft corals. These colonial polyps live in a fleshy matrix embedded with calcareous spicules. The soft corals are also known as octocorals because each little polyp has eight tentacles. A variety of colorful soft corals brighten the marine gardens on the rocky substrate of Gray's Reef off Sapelo Island.
Photo of orange-colored coral gobie fish on an orange soft coral. Source=Own work by uploader |Author=Nhobgood Nick Hobgood |Date=11/28/06 licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Two species of soft coral also grown on sandy bottoms close to shore, and can be found washed up on the beach.
One of these is the sea whip, Leptogorgia virgulata. Sea whips grow in clumps of whip-like strands on shelly sand. They are host to a community of little shrimps, fish, and snails that live on and around the corals. These communal creatures often assume the red, yellow, orange, or purple hue of the particular sea whip that they inhabit. After a sea whip dies, the covering of coral polyps erodes away, leaving a flexible black inner core, or whip. The dead whip is a favorite site for the growth of bryozoans, and sometimes is completely covered with white lacy crusts or rubbery dead man's fingers.
Sea Pansy. by Andrea Westmoreland from DeLand, United States —
License CC BY-SA 2.0 via Wikimedia Commons -https://www.dnr.sc.gov/marine/sertc/ octocoral%20guide/ Renilla%20_reniformis.htm
The other common soft coral found offshore is the sea pansy, Renilla reniformis. The sea pansy looks nothing like a coral; it is a round purple leathery pad one to two inches in diameter on a short stalk. Close inspection, though, reveals lighter-colored polyps scattered over the upper surface of the pad. In a container of seawater, each of the polyps extends eight tiny tentacles. Colonies of sea pansies grow on sandy bottoms close to the beach; at very low tides, patches of these soft purple octocorals are sometimes exposed. A small black-and-white-striped nudibranch, which is a shell-less gastropod similar to a terrestrial slug, is a specialized predator of sea pansies. At night, sea pansies put on a light show of green bioluminescence. The chemicals the sea pansy produces to make its light are similar to the chemicals that fireflies use to glow. These light-producing chemicals have been studied since the 1960's by researchers at the University of Georgia and elsewhere, and have become important in medical biochemistry research.