Spectacular Facts About Sea Fans (Gorgonians)

What are sea fans?

Sea fans are a type of soft coral that are often found in warm waters and around reefs. There are also soft corals that live in deep waters. Sea fans are colonial animals that have a beautiful, branching structure that is covered by soft tissue.​ This image shows sea fans around a shipwreck.

Gorgonians are in the class Anthozoa, which also includes other soft corals (e.g., sea whips), sea anemones, and stony or hard corals. They are in the subclass Octocorallia, which are soft corals that have eightfold radial symmetry. 

Sea fans have feathery polyps.

Like other corals, gorgonians have polyps. The polyps have tentacles arranged as a pennate, which means they have one main tentacle with branches off of it, like a feather. They can withdraw into the leathery tissue of the coral.

Feeding

Sea fans use their polyps to trap small food particles, such as phytoplankton and bacteria. The sea fan usually grows so that it is best oriented for the prevailing water current to flow over the polyps for food to be easily trapped.

The polyps are connected by fleshy tissue. Each polyp has a digestive cavity, but it is connected by tubes in the tissue. The whole sea fan is supported by a central axis (which looks a bit like the stem of a plant or trunk of a tree). This is made of a protein called Gorgon, the root of the name gorgonian. Although this structure makes the sea fan look like a plant, it is an animal.

Some gorgonians are inhabited by zooxanthellate, dinoflagellates that conduct photosynthesis. The gorgonian benefits symbiotically from the nutrients produced during that process. 

Sea fans host other marine life.

Sea fans may support their own community of creatures. Tiny pygmy seahorses perch on their branches, using their long, prehensile tails to hold on. One type of seahorse that lives on these corals is the common pygmy or Bargibant's seahorse. This seahorse has two color morphs—one a pinkish color and one yellow. The seahorses have knobby bodies that blend in perfectly with their coral home. Can you see the pygmy seahorse in this image?

Bivalves, sponges, algae, brittle stars, and basket stars also live on sea fans.

Sea fans are colorful.

Gorgonians can get pretty large, up to 3 feet tall by 3 feet wide. They can be a variety of colors, including pink, purple, yellow, and sometimes white. You can see a colorful collection of sea fans in this image. 

Although the sea fans have branches, most of these organisms are flat, rather than bushy.

Sea Fan Reproduction

Some gorgonians reproduce sexually. Male and female colonies of sea fans broadcast sperm and eggs into the water column. The fertilized egg turns into a planula larva. This larva swims at first and then metamorphoses and settles to the bottom and becomes a polyp.

From the first polyp, additional polyps bud to form a colony. 

These corals may also reproduce asexually, such as when they bud from one polyp, or produce a new colony from a fragment of coral. 

Sea fans may be used as souvenirs.

Sea fans may be collected and dried and sold as souvenirs. They are also harvested or grown for display in aquariums.

One of the best ways to enjoy sea fans is in the wild. Sea fans create a colorful, calming presence while you're scuba diving or snorkeling near a coral reef. 

Sources:

• Coulombe, D.A. The Seaside Naturalist. Simon & Schuster, 1984.
• Gorgonians (Gorgonacea) on the Shores of Singapore, http://www.wildsingapore.com/wildfacts/cnidaria/others/gorgonacea/gorgonacea.htm.
• Meinkoth, N.A. National Audubon Society Field Guide to North American Seashore Creatures. Alfred A. Knopf, 1981.
• Sprung, J. “Aquarium Invertebrates: Caribbean Gorgonians: Beauty in Motion.” Advanced Aquarist, 17 Sept. 2010, https://www.advancedaquarist.com/2004/3/inverts.