Corky Sea Finger
Purple Corky Finger, Deadman's Finger, Moss Coral
Briareum asbestinumPhoto © Animal-World: Courtesy David Brough
Caribbean Corky Finger, Sea Stalk Briareum
The Corky Sea Finger is a robust beginner's soft coral that is 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. This finger-like gorgonian grows over other gorgonians to form its shape. 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 common names they are known for are Purple Corky Finger, Moss Coral, Caribbean Corky Finger, Sea Stalk Briareum, and Deadman's Finger.
Getting a specimen with green tentacles and a purple base makes for quite a glow under actinic lighting! The Corky Sea Finger has a mat that is purplish gray or tan with slightly raised calyces that are more of a nub than a tube. Out of those projections are long grass-like polyps that are brown, pink, or green. The polyps are always expanded unless an outside stimuli disturbs them, then they can retract fully. They are very robust and will eagerly encrust other living corals, especially other gorgonians.
The Briareum corals are often confused with the true Star Polyps. True Star Polyps are of the Pachyclavularia genus and have a bright purple to reddish color mat and very green, yellow or light green tentacles. A well known example is the Green Star Polyps Pachyclavularia (Briareum) violacea. Some experts treat these two genera as synonymous and the Pachyclavularia genera may eventually be reclassified as a member of the Briareidae family. Yet there appear to be important differences so it remains to be seen where they end up. Unlike the Pachyclavularia species, B. asbestinum has more of a purplish gray or tan mat and and it can shed a mucus 'sheet'. It can also form upright finger-like protrusions from its base while the Pachyclavularia species only seem to create folds in the mat.
These gorgonians can also resemble (though not closely related too) species from the Erythropodium genera, like the Encrusting Gorgonian E. caribaeorum. Some distinctions are that the polyps of the Briareum corals can reside in raised calyces or bumps on the surface rather than having a smooth surface like the Erythropodium. They can also form short upright extensions arising from the mat which are mostly absent from the Erythropodium species.
The Briareum genus is very easy to care for and the only requirement is moderate to strong turbulent water flow. They are happy with fluorescent lighting, and can handle an acclimation to Metal Halides as well. 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. 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.
To learn more about these fascinating Octocorals see:
What Are Gorgonians?
Types of Gorgonians, Sea Fans and Sea Whips
Distribution / Background Gorgonian Information: The Briareum genus was described by de Blainville in 1930. There are about 8 species and they are B. asbestinum, B. contortum, B. excavata, B. gorgonoideum, B. grandiflorum, B. hamrum, B. palmachristi, and B. stechei. The Briareum genus has been propagated in captivity. Some common names the Atlantic species are known for are Corky Sea Finger, Deadman's Finger, Sea Stalk Briareum, Moss Coral, and Encrusting Gorgonian. Common names Pacific species are known for are Pacific Encrusting Gorgonian and Star Polyps.
The Corky Sea Finger B. asbestinum was described by Pallas in 1766. This is the most well known species which will encrust and grow protrusions.
True Star Polyps or the Pacific Star Polyps are of the Pachyclavularia genus. They have a bright purple to reddish colored mat and very green, yellow, or light green tentacles.
Where Briareum Corals Are Found: 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. B. asbestinum is found in the Western Atlantic in the Caribbean, Bahamas, Southern Florida and Bonaire.
Briareum Coral Habitat: The Briareum genus are very common and found on all reef areas. 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 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.
Description What do Briareum Corals look like: The Briareum genus are encrusting gorgonians. They form mats that are purplish gray or tan with slightly raised calyces that are more of a nub than a tube. Out of those projections are long grass-like polyps that are brown, pink, or green. The tentacles of the Pacific species are usually green while they are brown in the Atlantic species.
The Corky Sea Finger B. asbestinum is a finger-like gorgonian. It forms mats that are purplish gray or tan with slightly raised calyces that are more of a nub than a tube. They grow over other gorgonians to form these shapes.
The polyps are always expanded unless an outside stimuli disturbs them, then they can retract fully. They generally cover over other corals, but prefer to take over gorgonians. Other gorgonian species will encrust over whatever is available. They can grow 2 to 4 inches per year (4 - 10 cm) and can grow up to 2 feet in height (.61 m).
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. This is being used to show the different terpenoids or other chemicals produced by each gorgonian species
Difficulty of Care Gorgonian Care: The Corky Sea Finger B. asbestinum is very easy to care for and the only requirement is moderate to strong turbulent water flow. Most light is acceptable, although they grow faster with higher light levels. 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. Please be careful when handling since they are one of the most noxious of the gorgonians known to scientists.
Foods / Feeding Gorgonian Feeding: In the wild, Briareum corals have developed several feeding strategies. They capture microscopic food particles from the water column and can absorb dissolved organic matter. Unlike a lot of other Gorgonians, the Corky Sea Finger B. asbestinum 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 use a mucus net to capture particulate matter. Feed live enriched artemia nauplii and other similar sized foods.
Aquarium Care Stable tank conditions are needed to keep the Briareum genus. Doing water changes of 20% a month or 10% biweekly is needed, although it is suggested that doing 5% water changes once a week will replenish many of the needed additives. Iodine, calcium, strontium, and other trace elements can be added to maintain proper levels for good growth. The Briareum genus is also one of the most noxious of the gorgonians, with B asbestium being one of the most toxic species known to scientists at this point. So using media that helps to absorb toxins is suggested.
Suggested levels for Briareum species are:
- Calcium: 400 - 450 ppm
- Alkalinity: 3.2 - 4.8 MEQ/L (8 to 11 dKh - 10 is recommended)
- Phosphates: 0, zero.
- Magnesium: 1200 - 1350 ppm. (Magnesium makes calcium available, so if your calcium is low, check your magnesium levels before adding any more calcium.)
- Strontium: 8 - 10
|Quick Reference Chart|
A typical live rock/reef environment is what is needed for your Corky Sea Finger, along with some fish for organic matter production. The B. asbestinum will rapidly spread, so 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
Provide proper lighting and water movement. They are highly adaptable to any lighting but will do well with better lighting, and a good water flow is essential. 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.
- Minimum Tank Size / Length: 50 gallon (190 L) or larger
- Marine Lighting: Moderate to high
- Temperature: 72° - 78° F (20° - 26° C)
- Salinity / Specific Gravity: 1.023 - 1.025
- Water Movement: Moderate and turbid
- Water Region: Bottom of the aquarium
Compatibility and Social Behaviors The Corky Sea Finger is very aggressive in that it will grow encrust other corals, but prefers to take over gorgonians. This genus needs to be contained, or it will over grow nearby corals. They can be put on the sand, 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.
Breeding and Reproduction The Briareum genus will form daughter polyps from the edge of their mat as well as release gametes into the water. Some species will form planulae with their young brooding on the surface of the colony.
Propagation is easy, just please use gloves when handling. Simply cut off pieces of a branch or mat and glue them (use cyanoacrylate glue), or better yet, rubber band them to a rock or plug. You can also train them to spread onto rubble that can be easily snipped apart as needed.
Potential Problems The Briareum genus is hardy and very easy to care for. However they are susceptible to detritus collecting, and algae growing in-between their stalks if the water is not at least moderate and turbulent.
- Animal-World References: Marine and Reef
- 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
- Bob Goemans, Caribbean Corky Finger, Deadman Fingers, Animal Library, Saltwatercorner.com