This image of a giant sea fan was taken by NOAA photographer LCDR Eric Johnson on the Great Barrier Reef off the eastern coast of Australia. Sea fans are one of the most common coral structures found in this area. Sea fans belong to a group of coral known as gorgonians. These structures are build by thousands of tiny animals known as polyps. They secrete a substance that builds the coral into a crisscrossing lattice of interlacing filaments. Sea fans can often be seen waving in the current on a coral reef. They can grow to be several feet in diameter.