Corky Sea Finger

The “furry” Corky Sea Finger is a robust beginner’s soft coral. It’s very easy to care for and reproduce!

The Corky Sea Finger Briareum asbestinum, often called the Purple Corky Finger, has a beauty all its own. In the wild it is normally seen in a small, low-growing clumps, most often with one or more erect, finger-like rods rising from it. The rind of the mat and rods is purple to pale gray, or yellowish brown to tan, with slightly raised calyces that are more of a nub than a tube. Long, grass-like brownish green to light tan polyps extend from the calyces, giving it a “furry” appearance.

The Briareum genus is found in both the Atlantic and Pacific Oceans. These finger-like gorgonians grow over other gorgonians to form their shape. The Corky Sea Fingers are found in the Western Atlantic Ocean. They inhabit all areas of the reef in conditions with both pristinely pure waters as well as nutrient rich waters. They are the most collected gorgonian species since they are commonly found in shallow waters only knee deep. Some other common names they are known by are Sea Stalk Briareum, Deadman’s Finger, Caribbean Corky Finger, Moss Coral, Corky Finger Gorgonian, and Encrusting Gorgonian.

The Corky Sea Finger is durable and very easy to care for, its only requirement is a moderate to strong, and turbulent, water flow. This coral is very robust however, and will eagerly encrust other living corals, especially other gorgonians. Its polyps are always expanded unless an outside stimuli disturbs them, then they can retract fully. If you find these on the reef and gently fan your hand above the polyps they will quickly close leaving only their pretty purple rind exposed. Getting a specimen with green tentacles and a purple base makes for quite a glow under actinic lighting!

The Corky Sea Fingers are happy with fluorescent lighting and can handle acclimation to Metal Halides as well. This is a great beginners coral and a wonderful candidate for those who want to try propagation techniques. But please be careful when handling since they are one of the most noxious of the gorgonians known to scientists. It may be helpful to keep the colony on a rock that isn’t connected to any of the rock work, or they may spread and take over some corals.

To learn more about these fascinating Octocorals see:
What Are Gorgonians? Types of Gorgonians, Sea Fans and Sea Whips

Habitat: Distribution / Background

The Corky Sea Finger Briareum asbestinum was described by Pallas in 1766. Some other common names this species is known by include Purple Corky Finger, Sea Stalk Briareum, Deadman’s Finger, Caribbean Corky Finger, Moss Coral, Corky Seafinger, Corky Finger Gorgonian, Encrusting Gorgonian, and Briareum.

About the Briareum Genus:

The Briareum genus was described by de Blainville in 1834. There are about 7 species in this genus including B. asbestinum (Pallas, 1766), B. contortum (Kükenthal, 1906), B. excavata (Nutting, 1911), B. hamrum (Gohar, 1948), B. palmachristi (Duchassaing & Michelotti, 1860), Pacific Encrusting Gorgonian B. stechei (Kükenthal, 1908), and B. violaceum (Quoy & Gaimard, 1833).

The Briareum genus are found in both the Atlantic and Pacific Oceans. In the Western Atlantic they are found along the US and Canadian coasts as well as in the Caribbean. Some common names the Atlantic species are known by are Encrusting Gorgonian and Briareum. Common names Pacific species are known for are Pacific Encrusting Gorgonian and Star Polyps.

The Briareum corals are very common and found on all reef areas, and are not on the IUCN Red List for Endangered Species. These corals inhabit depths from 3 to 131 feet (1 – 40) with some species, like the Pacific Encrusting Gorgonian B. stechei, even found in just ankle deep water. The waters vary, having strong or weak water movement. The waters can also be very clean or very nutrient rich, and they can have varying amounts of lighting.

These are soft corals in the Class Anthozoa, Subclass Octocorallia, and Order Alcyonacea. They are currently classified as a gorgonian under the Suborder Scleraxonia, which have fused sclerites in their core and rind. The Briareum genus is further placed in the Briareidae family. This family originally had just this single genus, but has been recently revised to include two additional genera, Lignopsis (Perez & Zamponi, 2000) and Pseudosuberia (Kükenthal, 1919), each if which have just a single species.

The classification of gorgonians in general is done by some simple visual clues such as colony size, shape, axis structure, color, polyp placement, and pattern of branches. Getting a little more technical, they also look to see if the polyp is autozooid or siphonozooid. Then there is the more exacting use of chemotaxonomy, used to show the different terpenoids or other chemicals produced by each gorgonian species.

The Briareum corals from the Atlantic can resemble species from the Erythropodium genera, like the Encrusting Gorgonian E. caribaeorum. Although they are both encrusting gorgonians, however, they not closely related and there are some distinctions. The polyps of the Briareum corals reside in raised calyces or bumps on the surface while the Erythropodium species have a smooth surface. The Briareum species can also have short upright extensions arising from the mat which are mostly absent from the Erythropodium species.

Pacific species of Briareum corals, known as Pacific Encrusting Gorgonians and Star Polyps, are often confused with the true Star Polyps of the Pachyclavularia genus. A well known example is the Green Star Polyps Pachyclavularia (Briareum) violacea that also has a bright purple to reddish colored mat and very green, yellow or light green tentacles. Some experts treat these two genera as synonymous and eventually the Pachyclavularia genera may be reclassified as a member of the Briareidae family. However there appear to be some important differences, so it remains to be seen where they end up. Unlike the Pachyclavularia species, Briareum corals can form upright finger-like protrusions from their base while Pachyclavularia only seem to create folds in the mat.

About the Corky Sea Finger:

The Corky Sea Finger is found in the Western Atlantic in the Caribbean, Bahamas, Southern Florida and Bonaire. They are found along upper reef edges in coral reefs and on rocky bottoms from 3 to 40 feet (.5 to 12 meters). This is the most well known Briareum species. It is an encrusting coral that will overtake other gorgonians, and will also grow finger-like protrusions.

They have relatively few nematocysts, so have lost the abilities to capture particulate foods from the water column. They relying instead on a mucus coating they produce to capture food particles. They will then shed this mucus layer from their surface about every 10 days, depending on the amount of sediment and bacteria that has collected. Corky Sea Fingers obtain other nutrients from the marine algae, zooxanthellae, which they have a symbiotic relationship with.

The Corky Sea Finger is one of the most toxic of the known gorgonians, as it secretes a number of terpenes and acetogenins. The level of toxicity for this species is linked to the depth they are found, with deeper specimens emitting stronger levels of terpenoid compounds. Interestingly, the primary terpenoid compound it secretes is asbestinane, which may be isolated to just this species. Predators include the Flamingo Tongue Snails Cyphoma spp. that feed on a variety of gorgonians.

• Scientific Name: Briareum asbestinum
• IUCN Red List: NE – Not Evaluated or not listed

Description

The Corky Sea Fingers are encrusting gorgonians. In the wild colonies are normally small, low-growing clumps, most often with one or more erect, cylindrical rods arising from them. They grow over other gorgonians to form these shapes. They will cover over other corals, assuming their shape, but they prefer to take over gorgonians. Aside from that, they are not picky and will even encrust over loose rubble and rock..

Most specimens are collected from shallow waters with high water flow and strong illumination. Shallow water specimens they tend to form fat, vertical fingers, sometimes with short lateral branches. Specimens from deeper, calmer waters with less light tend to form tall, thinner protrusions without any branches. They can grow 2 to 4 inches (4-10 cm) per year and the cylindrical rods can reach up to 24″ (61 cm) in height.

The rind of the mat and rods are purple to pale gray or yellowish brown to tan. The rind is dotted with slightly raised calyces that are more of a nub than a tube. Long grass-like polyps extend out of the calyces giving them a “furry” appearance. The polyps are always expanded unless an outside stimuli disturbs them, then they can retract fully. The tentacles of the Corky Sea Finger and other Atlantic species are light tan to brown while in the Pacific species they are usually green.

• Size of organism – inches: 24.0 inches (60.96 cm) – Height of vertical protrusions.
• Lifespan: – unknown

Difficulty of Care

The Corky Sea Fingers are moderately hardy and easy to care for, making them great for beginner aquarists. These are one of the most adaptive corals in the wild. Although they are photosynthetic, they need less light than many other corals. They are about as forgiving as any coral can get and still be considered symbiotic. They also have a high tolerance for both turbidity and a wide range of water movements. However, they grow most rapidly with moderate water movement and bright light.

They need a moderate, turbulent water flow. If the water flow is too slow they can succumb to cyanobacteria and algae. However if it is too strong, and especially with a more linear movement, it will interfere with polyp extension and the coral’s ability to feed. Unlike some of the other species in this genus, they need good lighting. In fact, the stronger the light, the faster they will grow.

They may spread and take over some corals, so it is helpful to keep the colony on a rock that isn’t connected to the rest of the rock work. These corals make a wonderful candidate for those who want to try propagation techniques. But they are also one of the most noxious of the gorgonians known to scientists, so please be careful when handling. Using a filter media, like Poly Filter, can help absorb the toxins.

• Aquarium Hardiness: Moderately hardy
• Aquarist Experience Level: Beginner

Foods and Feeding

In the wild, Corky Sea Fingers have developed a couple feeding strategies. They capture microscopic food particles from the water column and can absorb dissolved organic matter. Their polyps do not feed on zooplankton, rather the Corky Sea Finger uses a mucus layer to catch particulates from the water column for part of its nutrition. They create this mucus cover over their surface and then about every 10 days, they will retract their polyps to allow the mucus to slough off. Unlike a lot of other Gorgonians, the Corky Sea Finger also has a symbiotic relationship with a marine algae known as zooxanthellae, where they also receive some of their nutrients.

In captivity, the Corky Sea Finger will use light and their zooxanthellae for a food source, and will also create a mucus net to capture particulate matter. On a weekly basis, feed live enriched artemia nauplii and other similar sized plankton like foods. Stirring the substrate to suspend edible particulates is also helpful. along with the presence of fish, which can also help provide nourishment as well.

• Diet Type: Omnivore – Nutrition is obtained from capturing phytoplankton and food particulates from the water column with a mucus net, and from the symbiotic marine algae, Zooxanthellae.
• Flake Food: No – Will not eat this.
• Tablet / Pellet: No – Will not eat this.
• Live foods (fishes, shrimps, worms): Some of Diet – Tiny live plankton.
• Liquid Foods: Some of Diet – Marine snow and other phytoplankton preparations.
• Meaty Food: Some of Diet – Enriched artemia nauplii and other similar sized plankton like foods.
• Feeding Frequency: Weekly

Aquarium Care

Stable tank conditions are needed to keep the Corky Sea Finger and other members of the Briareum genus. Water changes of 10% biweekly or 20% a month is needed, although it is suggested that doing 10% water changes once a week will replenish many of the needed additives and help keep water conditions high.

Iodine, calcium, strontium, and other trace elements can be added to maintain proper levels for good growth. The Corky Sea Finger s also one of the most noxious of the gorgonians known to scientists at this point. Using filter media that helps to absorb toxins, like poly fiber, is suggested. Phosphates should be maintained as close to zero as possible and pH between 8.2 and 8.4.

• Water Changes: Bi-weekly – To keep water stable, test weekly.
• Calcium Levels: 400.0 – 450.0 ppm – If using Seachem’s calcium, 385 should suffice.
• Alkalinity Levels: 8.0 – 11.0 dKH – 10 dKH is recommended.
• Magnesium Levels: 1,250.0 – 1,350.0 ppm – Magnesium makes calcium available, so if your calcium is low, check your magnesium levels before adding any more calcium.
• Strontium Levels: 8.0 – 10.0 ppm
• Iodine Levels: – May benefit from supplemental additions, dose per recommendation on label.

Aquarium Setup

The Corky Sea Finger can reach up to 24″ in height and may need a tank to accommodate this eventual size. A tank that is at least 50 gallons and 24″ deep is needed to provide room for growth. Other Briareum species may need a taller or not as tall tank. A mature tank (well over a year old) is also advised to increase the successful life span of Briareum corals.

Quick Reference Chart
Lighting:
Water Flow:
Temperament:

A typical live rock/reef environment, along with some fish for organic matter production, is needed for it to thrive. Provide proper lighting and water movement. They are highly adaptable to any lighting but will thrive best with bright lighting, Lighting can be provided with fluorescent like T5s, bright LEDs, or they can handle acclimation to Metal Halides as well. The water temperature needs to be kept lower than some corals, between 68° and 75°F (20° to 24° C). Provide stronger light in tanks over 30″ deep.

The Corky Sea Finger can grow rapidly, so it may be helpful to keep the colony on a rock that isn’t connected to any of the other rock work to keep them from spreading and taking over other corals. A sandy substrate is best since this coral will spread onto any hard surface, including rubble and possibly more stationary substrates like crushed coral. Placing them on a “rock island” surrounded by sand will help prevent their spreading to other hard surfaces and onto corals. Also stirring the sand bed, it releases nutrients into the water column that it can ingest.

Water movement should be moderate and turbulent, but not to the point of stirring up sediment onto their mucus coat, since this will cause them to shed more often than normal. They produce a mucus sheet which they use for feeding. Every 10 days or so, they may slough off this mucus sheet to keep bacteria and sediment from collecting. If they are in more turbid water they will do this less often. However, too strong of a water movement, especially if it is linear rather than turbulent, will prevent proper mucus feeding ability. Low water movement will cause cyanobacteria and algae to overtake your Corky Sea Finger and will not allow proper polyp expansion.

• Minimum Tank Size: 50 gal (189 L) – A 50 gallon tank or larger that’s at least 24″ tall.
• Suitable for Nano Tank: No
• Live Rock Requirement: Typical Amount – Separate the colony from other rock work to help prevent them from spreading onto other corals.
• Substrate Type: Sand – Will not spread onto sand and uses nutrients from it when its stirred up.
• Lighting Needs: Moderate – normal lighting – Will grow faster in strong lighting.
• Temperature: 68.0 to 75.0° F (20.0 to 23.9&deg C) – Seems to need lower temperatures to stay healthy.
• Specific gravity: 1.023-1.025 SG
• Water Movement: Moderate – Moderate and turbulent.
• Water Region: Bottom – On a “rock island” in the sand.

Social Behaviors

The Corky Sea Finger is very aggressive in that it will grow rapidly and encrust other corals. This genus needs to be contained, it prefers to take over gorgonians but will spread onto any hard surface. They can be put on the sand or a “rock island” away from the main rock work, and they will stay put. Putting it among the rock work will encourage growth onto the rocks and slowly over other corals.

Most fish will avoid chewing on this coral, however, Butterflyfish are known to feed on gorgonian polyps or tissue, so keep an eye on them. Some angelfish will also pick at the polyps, but can be housed with them if the angelfish is well fed. Other fish in the tank benefit the Corky Sea Finger in that they provide nutrients for the coral with their waste. Avoid the Flamingo Tongue Snails Cyphoma. which are readily available for purchase, since they will eat your gorgonian, and also avoid snails from the Murex genus.

• Venomous: No – Still, it does have noxious toxins on the surface.
• Temperament: Aggressive
• Compatible with:
  • Same species – conspecifics: Yes
  • Anemones: Safe
  • Mushroom Anemones – Corallimorphs: Monitor – May grow over and kill these if given the opportunity.
  • Leather Corals: Monitor – May overgrow these if given the opportunity.
  • Zoanthids – Button Polyps, Sea Mats: Monitor – May grow over and kill these if given the opportunity.
  • Sponges, Tunicates: Threat – Will overgrow these if given the opportunity.
  • Starfish: Safe
  • Feather Dusters, Bristle Worms, Flatworms: Safe
  • Clams, Scallops, Oysters: Monitor – May grow over the shell area and irritate the species.
  • Crabs: Threat
  • Snails: Monitor – While most snails are safe, Murex genus snails and Flamingo Tongue snails will eat gorgonians.
  • Sea Apples, Cucumbers: Monitor – Gorgonian may die if these animals expel their toxins.
  • Urchins, Sand Dollars: Safe
  • Nudibranch, Sea Slugs: Monitor – Should be safe, no way of knowing if any and all species are safe.
  • Copepods, Amphipods, Mini Brittle Stars: Safe
  • Stony Corals: Threat – is aggressive – Will grow over and kill these if given the opportunity.
  • Soft Corals: May be aggressive – May grow over and kill these if given the opportunity.

Sex: Sexual differences

There are no discernible sexual differences.

Breeding / Reproduction

The Briareum genus has been propagated in captivity. The Corky Sea Finger reproduces by pseudo-runner/stolon growth, as well as releasing gametes into the water. Once the runner-like branches attach to the substrate and form a new colony, they will separate from the parent colony. They are unique from other gorgonians in that they will brood their larvae right on the surface of the colony. They also reproduce through fragmentation of the vertical finger-like protrusions that grow from the mat.

Propagation in captivity is easy, but because they have noxious toxins on the surface, be sure to use gloves when handling. Simply cut off pieces of a branch or mat. Glue them to a rock or plug using cyanoacrylate glue, or attach them with a rubber band. You can also train them to spread onto rubble, which can then be easily snipped apart as needed Some aquarists will take sheets and attach them to objects in the tank that need some “disguising,” like intake lines or overflow boxes.

• Ease of Breeding: Easy

Ailments / Diseases

The Corky Sea Finger, as well as the entire Briareum genus, is hardy and very easy to care for. However they are susceptible to collecting detritus and to algae and cyanobacteria accumulating on its branches.They can get red band and black band infections that are caused by cyanobacteria. Keeping a moderate and turbulent water flow will help prevent this. If your gorgonian does get this, you can at times cut off the bad part and hope the rest will recover. Freshwater dips can also kill cyanobacteria, and are an effective treatment.

• Black Band Disease (BBD)
  This ailment is characterized by a leading band of black gooey material (mostly algae), which leaves a denuded skeleton behind. The bare skeleton then becomes covered with many species of algae. You can use a needle to lift the black band from the coral skeleton. With a small diameter airline tubing, siphon the black front away, catching any loosened debris as well. If it is not possible to remove all of the black band, you may be able to treat the area directly by applying a small amount of Erythromycin or Chloramphenicol.
• Red Band Disease (RBD)
  As the name “red band” indicates, this ailment is characterized by a brick red or dark brown band. The band is a soft microbial mat which will easily dislodge from the surface of the coral.

The Briareum species may also be a food source for Flamingo Tongue Snails Cyphoma spp. and snails from the the Murex genus.

Availability

The Corky Sea Finger is easy to find at pet shops and online, and they are moderately inexpensive for 5†to 14†tall specimen.

References

• Animal-World References: Marine and Reef
• Briareum asbestinum (Pallas, 1766) corky seafinger, SeaLifeBase
• Briareum asbestinum (Pallas, 1766), WORMS World Registry of Marine Species
• Eric Borneman, Aquarium Corals : Selection, Husbandry, and Natural History , TFH Publications, 2001
• Anthony Calfo, Book of Coral Propagation, Volume 1 Edition 2: Reef Gardening for Aquarists, Reading Trees; 2nd edition, 2007
• Harry Erhardt and Horst Moosleitner, Marine Atlas Volume 2, Invertebrates (Baensch Marine Atlas), Mergus Verlag GmbH, Revised edition, 2005
• Ronald L. Shimek, Guide to Marine Invertebrates: 500+ Essential-to-Know Aquarium Species, Microcosm, 2005
• Julian Spring and J. Charles Delbeek, The Reef Aquarium: A Comprehensive Guide to the Identification and Care of Tropical Marine Invertebrates (Volume 1), Ricordea Publishing, 1994
• Bob Goemans, Caribbean Corky Finger, Deadman Fingers, Animal Library, Saltwatercorner.com

Featured Image Credit: ABS Natural History, Shutterstock