Venus Sea Fan, Gorgonia flabellum

Venus Sea Fan, Gorgonia flabellum. Underwater photograph taken in the coastal waters off Bonaire, Caribbean Netherlands, December, 2019. Photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:  The Venus Sea Fan, Gorgonia flabellum (Linnaeus, 1758), is an octocoral in the Gorgoniidae Family of Gorgonians. The Gorgoinia genus is one of thirteen genera in this family, and there are nine species in this genus. They are also know as the Bahamian Sea Fan and the West Indian Sea Fan.

Morphology: The Venus Sea Fan is a colonial soft coral with polyps that have eight-fold radial symmetry. Their eight tentacles are pinnate (having a feather-like appearance). The polyps have a flower-like appearance, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. As octocorals, they have tiny spine-like hard parts in their bodies called sclerites (or spicules) that give them some degree of support. This coral grows in the form of a fan, composed of a lattice of branches in a single plane. The coral grows from a small base, forming several main branches with side branches and a network of small branchlets. The branches have a central core, which is made of a horn-like substance called gorgonin. Gorgonin is a protein which is exclusive to the gorgonians and which contains significant amounts of iodine and bromine. The sclerites are located in the solid core. The polyps are embedded in a gelatinous material (called the coenenchyme) which surrounds the core. The fan is usually oriented perpendicular to the prevailing current, to assist with food gathering. Venus Sea Fans are pale lavender, tan, white or yellowish in color. They reach 1.5 m (4.9 feet) in height.

Diet:  Venus Sea Fans are zooxanthellate. They have a symbiotic relationship with single-cell dinoflagellates, known as zooxanthellae. Zooxanthellae live within certain coral polyps, sea anemones, jellyfish, and nudibranchs. The zooxanthellae produce energy, during daylight, by means of photosynthesis. This energy is passed along to their hosts, sometimes providing up to 90% of the host’s total energy needs. In return, the host provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zooxanthellae. Venus Sea Fans supplement the energy provided by zooxanthellae by using their tentacles to capture amphipods and other plankton from the surrounding water. The tentacles then pass the food to the mouth. Because these polyps cannot change location, they are found in areas where moving water, caused by wave action or current, brings them more food.

Predators: There is limited documentation of predators of Venus Sea Fans. Angelfish, butterflyfish, nudibranchs, and the Flamingo Tongue Shell, Cyphoma gibbosum, are known to feed, to varying degrees, on this species.

Reproduction: Venus Sea Fan colonies are gonochoric (male or female). Reproduction is primarily asexual, through fragmentation. When a piece of branch is broken away from the colony, and lands in a suitable habitat, it can start growing a new colony. Reproduction can also be sexual. Sexual reproduction is accomplished through broadcast spawning, with external fertilization. The gametes are shed into the coelenteron and spawned through the mouth. The zygote develops into a planktonic planula larva. Metamorphosis begins with early morphogenesis of tentacles, septa and pharynx before larval settlement on the aboral end.

Ecosystem Interactions: The Venus Sea Fan’s have symbiotic relationship with zooxanthellae; they also host several parasites. Cyanobacteria, especially filamentous Oscillatoriales, can cause tissue necrosis and disrupt the sea fan’s structure. Aspergillus Fungus can also cause serious tissue damage in this species. Ectoparasitic copepods from the genus Sphaerippe cause galls to form on the fan branches.

Human Interactions: Historically, Venus Sea Fans have been significantly harmed by human activities such as dredging, anchoring of vessels, water pollution, and aquarium and curio collecting. Venus Sea Fans are now protected throughout most of their range and most of these threats have lessened. All corals, including Sea Fans may be damaged by  sediment or by being handled or stepped on by snorkelers, divers, or other beach goers. From a conservation perspective the Venus Sea Fan has not been formally evaluated. It is fairly common and widely distributed and should be considered to be of Least Concern.

Synonyms: Busella occatoria, Gorgonia flabellum f. occatoria, Rhipidigorgia flabellum, Rhipidigorgia occatoria, Rhipidogorgia elegans, and Rhipidogorgia flabellum.