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Interesting Facts about Sea Fans

[Sea Fan Phylum: Cnidaria] [Class: Octocorallia] [Order: Malacalcyonacea] [Family: Gorgoniidae]

The genus Gorgonia contains around five hundred (500) different types of sea fans (known as gorgonians). Most of the soft coral sea fan classification is represented by a variety of fanlike formations.

This section contains information about sea fan corals, including where they are found, what they eat, and how the colonies of tiny polyps grow into huge fanned out structures.

Gorgonian Sea Fan Coral Habitat and Range

Like most filter-feeding soft corals, the gorgonians also need a marine environment with current-rich, warm water.

Worldwide, the predominant regions to find sea fans are tropical and subtropical reefs, but especially:

Despite being less common, some sea fan species also inhabit the deeper terrains of the transition zones in some temperate waters (many thousands of metres deep).

Nonetheless, they are strictly 'marine invertebrates' that would not survive in brackish or freshwater environments.

Instead, they thrive best when they can attach themselves to robust substrates, such as coral reefs, rocks, or even the skeletons of dead corals.

Here's the thing:

The optimum depth range for most types of sea fans is quite shallow, for strong sunlight penetration. As a result, the typical sea fan habitat will be between ten (10) and forty (40) metres (30 to 130 feet) below the surface.

Furthermore, the colonies of tiny filter-feeding polyps grow a lot faster in areas with strong water currents, due to a rich supply of plankton and other microscopic food particles.

Characteristics of Sea Fan Coral

So, what exactly is a sea fan? Using simplified sea life terminologies, the basic definition of a sea fan is a delicate lace-like soft coral that belongs within the group of gorgonian sea fans (e.g., order Alcyonacea).

Unlike many of the hard coral species that create rigid reef structures, such as staghorn coral, the basic shape and formation of sea fans is usually a fan-shaped whippy structure that shakes and sways (without breaking) if ocean currents are strong.

Moving on...

Flexible scleroprotein (known as gorgonin) creates the main structural strength of the skeleton. In most species, it provides strong support for the outer branches of the colony - along with any additional branching nets or tissues.

Gorgonia flabellum: Sea Fans Facts and Species InformationSea fans grow in a variety of sizes and colours, especially those with subtle tones of red, purple, orange, and yellow.

The average size of a sea fan ranges between thirty (30) and 150 centimetres across.

Even so, the black sea fan coral (Iciligorgia schrammi) ranks among the biggest of all living sea fans, measuring up to two (2) metres tall (79 inches).

The Ecological Importance of Sea Fans

One of the little-known sea fan facts is that their branches provide essential shelter for a variety of marine organisms.

Not only do these elegant structures host brittle stars, pygmy seahorses, and shrimps, but they also help to filter sea water and contribute to the healthy biodiversity in coral reef ecosystems.

Interesting Fact: It's easy to think that common sea fans and sea whip corals are the same. Actually, both are types of gorgonians - and closely related - but they differ in several important ways.

What Do Sea Fans Eat?

As the tiny polyps grow, which may be as little as a few centimetres per year, they spread outwards and usually face the prevailing oceanic currents.

This adaptation creates a large surface area for them to ensnare their prey and sift plankton particles from the water column.

Types of Sea Fans

Bipinnate Sea Plume (Antillogorgia bipinnata)

Pseudopterogorgia bipinnata was the former gorgonia classification for bipinnate sea plumes (Antillogorgia bipinnata). They are soft corals that are commonly found throughout most of the Caribbean and western Atlantic Ocean.

With optimum conditions, such as healthy shallow reefs that get moderate to strong water movement, they will grow tall and flexible plume-like branches.

The bipinnate pattern of the branches (often called "twice-pinnate") grows from a central stem with paired side branches that extend in opposite directions.

Colour and Characteristics

Colouration of the bipinnate sea plume varies according to the amount of light it gets. But, they generally display hues of deep purple, violet, red, or tan, with small and fuzzy polyps.

They are efficient filter feeders that prefer high-flow areas. Hence, they're usually found anchored to hard structures (rocks or corals) ) between three (3) and thirty (30) metres deep.

The ecological role of Antillogorgia bipinnata should not be understated. The feathery, plumose shape and height provide good shelter and habitats for various species of marine invertebrates and small fish.

Sea Fan Facts: They are easy to spot on reef crests because they sway in the surge. But, even though they don't usually snap in strong water currents, making contact with gorgonians causes abrasions which are slow to recover.


Black Sea Fan (Iciligorgia schrammi)

Its common name is a little misleading because Iciligorgia schrammi looks more like one of the fragile red sea fan species. In fact, the inspiration for its common name comes from the dark coloured axis (interior skeleton).

Nonetheless, it is a gorgonian coral that inhabits the tropical western Atlantic, especially the Bahamas, the Caribbean Sea, Gulf of Mexico, and Florida.

Black sea fans grow on solid substrates, such as reef structures, overhangs, vertical walls, or ledges. They are generally tolerant of moderate water currents and they thrive best at depths between three and three hundred metres.

Description and Size

In general, the colonies are orange and reddish-brown, and the whip-like branches are long and flexible - albeit rather ragged and planar in appearance (like a large wavy hand fan).

As they develop, they form large, bushy sea fans that can eventually grow to more than one (1) metre in height.

The branches are smooth, most often with irregular formations, but they are prone to twisting or drooping. Even though the reef polyps get some stiffness from the sclerites, they are small enough to retract during the day.

Most gorgonian corals are suspension feeders, and black sea fan polyps also capture plankton, along with other kinds of organic particles that drift in the mid-water column.


Common Sea Fan (Gorgonia ventalina)


Graduated Sea Fan (Muriceides lepida)


Longspine Sea Fan (Muricea pinnata)


Multicoloured Sea Fan (Melithaea rubra)


Pink Sea Fan (Eunicella verrucosa)


Slim Sea Fan (Pseudopterogorgia americana)


Spiny Sea Fan (Muricea muricata)


Venus Sea Fan (Gorgonia flabellum)


Violescent Sea-whip (Paramuricea clavata)

How Do Sea Fans Reproduce?

Sea fan reproduction can occur in two distinctly different ways - sexually and asexual budding. Either way, both of these reproductive methods are vital for the long term survival of sea fan populations.

Sexual Reproduction

The primary method used by sea fans to create new colonies is "broadcast spawning". Most of the sea fan phylum has separate colonies of males and females (they are dioecious animals).

After releasing thousands of eggs and sperm into open water, usually aligned with temperature changes or moon phases, random fertilisation occurs.

Then...

Fertilised eggs develop into larval planulae before they eventually sink to the ocean floor and attach themselves to a suitable rigid surface (e.g. coral) and grow as a new colony. This is how sea fans can spread across large areas.

Asexual Reproduction

The process known as "asexual budding" is a way for damaged colonies to recover from fragmentation (e.g. pieces broken off by destructive storms).

Individual polyps, or fragments of the sea fan coral, reattach themselves to a substrate and begin to grow, thereby expanding the size of the colony.

Sea Fan Predators and Threats

Even though sea fan coral tends to be fairly resilient, a number of natural and human-induced activities threaten the long term survival of healthy reef ecosystems.

For example, some of the natural predators of sea fans cause large amounts of destruction, especially:

Whereas, some of the most damaging human-caused threats include coral diseases (e.g. Aspergillosis), climate change (including ocean acidification), underwater garbage pollution, and overfishing.

Pro Tip: The IUCN Red List of Threatened Species assessed the pink sea fan (Eunicella verrucosa) in 1996 and cites their conservation status as "Vulnerable" (VU).

Related Information and Help Guides

Note: The short video [3:21 minutes] presented by 'Deep Marine Scenes' contains more sea fan facts with footage showing how these colourful soft corals sway with ocean currents.

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