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Overview

Brief Summary

The dead man's finger is a soft coral, just as hard as cartilage. The branches are totally covered with small polyps. The polyps themselves have eight tentacles, but they are only visible with a very good magnifying glass. The polyps are readily frightened. If you were to brush against a dead man's finger, the polyps retract quickly into the coral skeleton. They only dare to come back out after several hours. If you don't see the polyps, the coral structure looks like a leathery finger.
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Biology

Colonies of dead man's fingers actively feed at various times of the day, with the polyps extended (1). They feed on plankton (2) which is brought into the polyps by the generation of a water current caused by the beating of tiny hair-like cilia. This also brings oxygen into the polyp (1). Colonies become inactive from July to December, when they seem to shrink back and develop a brownish or reddish colouration caused by the development of a coating of algae and hydroids. This time of inactivity coincides with the final stages of gonad development (1). Most colonies are either male or female, although a few hermaphroditic colonies arise (2), in which the polyps develop ova and testes. Colonies reach sexual maturity in the second year, but in some, maturity is delayed for a further year or two (1). Spawning occurs in December and January when the gametes (sex cells) are released into the water. Fertilisation takes place externally, and the embryos float in the water for one week before developing into active free-swimming larvae known as 'planulae larvae'. These settle, usually after around one or two days, on a suitable substratum and turn into polyps. In some cases, if a suitable site is not found, planulae larvae may survive for a prolonged period in the plankton, enabling them to disperse and eventually find a suitable site on which to settle (2). Colonies of dead man's fingers are known to live for over 20 years (1).
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Description

Dead man's fingers is a colonial soft coral that forms thick, fleshy and irregular masses, which are often finger-like in appearance (1). The colour varies and may be pink, orange, white, grey, or yellow. When submerged, the individual polyps that make up the colony are visible. Each polyp bears eight small tentacles, which gives the colonies a feathery appearance and has earned them the name of 'dead man's fingers' as they appear to be decomposing (2).
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Comprehensive Description

Description

 Mature colonies form thick, fleshy masses of irregular shape, typically of stout, finger-like lobes that usually exceed 20 mm in diameter. Young, developing colonies form encrustations about 5 -10mm thick. The height and breadth of colonies are up to 200 mm. Colonies are white or orange in colour, but may appear reddish or brownish during periods of inactivity when the polyps are withdrawn into the colony, owing to the development of a film of epibiota.May be confused with Alcyonium glomeratum, which prefers sites sheltered from wave action or tidal streams. It is blood red or rust coloured (occasionally pale orange or yellowish), has relatively slender branches, and a softer, more flaccid texture but a rough surface. In Alcyonium glomeratum the colonies are also more contractile, and cross sections through the fingers show numerous cavities.
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Description

Colonies of this common soft coral are variable in shape, forming large irregular masses up to 250mm high, usually with a few blunt 'fingers' which are usually more than 30mm in diameter. The colour varies from white to dull orange with yellowish or brownish colonies occurring occasionally; the polyps are translucent white. On the west coast of Ireland almost all colonies are orange in colour. The other two species of dead mens fingers in this area are Alcyonium glomeratum and Alcyonium hibernicum but these are much rarer and are unlikely to be confused with this species.
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Source: Encyclopedia of Marine Life of Britain and Ireland

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Distribution

Cape Hatteras to Bay of Fundy
  • North-West Atlantic Ocean species (NWARMS)
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Common on all coasts of Britain and Ireland and throughout the northeast Atlantic, south to Portugal.
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Range

This soft coral has a wide distribution around the coastline of the British Isles. Elsewhere it is found in Iceland and along the Atlantic coast of Europe from Norway as far south as the Bay of Biscay, but it does not extend into the Mediterranean (3).
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Ecology

Habitat

sandy, muddy, or rocky habitats; also may attached themselves to hard parts or products of other organisms (shells)
  • North-West Atlantic Ocean species (NWARMS)
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Depth range based on 722 specimens in 1 taxon.
Water temperature and chemistry ranges based on 161 samples.

Environmental ranges
  Depth range (m): 0 - 146
  Temperature range (°C): 6.433 - 12.863
  Nitrate (umol/L): 2.055 - 10.454
  Salinity (PPS): 33.138 - 35.352
  Oxygen (ml/l): 4.910 - 6.665
  Phosphate (umol/l): 0.333 - 0.837
  Silicate (umol/l): 2.052 - 5.948

Graphical representation

Depth range (m): 0 - 146

Temperature range (°C): 6.433 - 12.863

Nitrate (umol/L): 2.055 - 10.454

Salinity (PPS): 33.138 - 35.352

Oxygen (ml/l): 4.910 - 6.665

Phosphate (umol/l): 0.333 - 0.837

Silicate (umol/l): 2.052 - 5.948
 
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 Attached to rocks, shells and stones where the otherwise dominant algae are inhibited by a lack of light and occasionally on living crabs and gastropods. Generally found in situations where strong water movement prevails. Occasionally on the lower shore but more common sublittorally, down to about 50 m.
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Grows attached to bedrock, boulders, stones or shells, usually in places with strong water movement. From the lower shore to about 100m.
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Attaches to rocks, stones and other hard surfaces including living crabs (1). It may occasionally be found on the lowest levels of the shore at spring tide, but it is usually found below the intertidal zone down to depths of 50 m, and thrives in areas where the water movement is strong (2).
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Associations

Animal / predator
adult of Simnia patula is predator of flesh of Alcyonium digitatum
Other: sole host/prey

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Life History and Behavior

Behavior

Diet

Generally, anthozoans are primarly carnivorous which prey on sea urchins, gastropods, bivalves, or crustaceans that crawl or swim into their grasp.
  • North-West Atlantic Ocean species (NWARMS)
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Alcyonium digitatum

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File
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Statistics of barcoding coverage: Alcyonium digitatum

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
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Conservation

Conservation Status

Status

Not threatened (3).
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Threats

This species is not threatened.
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Management

Conservation

Not relevant.
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Wikipedia

Alcyonium digitatum

Alcyonium digitatum or dead man's fingers is a species of soft coral in the Alcyoniidae family. It is found around the coasts of the northern Atlantic Ocean.

Contents

Description

Dead man's fingers is a colonial coral forming clumps of yellow, white or cream-coloured fleshy masses of finger-like lobes. The surface layer include many sclerites which form a crust.[2] The individual polyps are white and translucent, and project from the leathery surface when feeding, giving the colony a furry appearance.[3]

Distribution and habitat

Dead man's fingers is found along the Atlantic coasts of north west Europe from Portugal to Norway. The species also occurs in parts of Canada and the north eastern coast of the United States, the Gulf of Maine and the Bay of Fundy.[4] The polyps live in colonies attached to bedrock, boulders, stones and occasionally the shells of crabs and gastropods. They are most plentiful in areas with strong water movement and where there is insufficient sunlight for algae to predominate. They are usually found in the sublittoral zone down to about fifty metres.[1] This coral is common around the coasts of Britain and Ireland where Alcyonium glomeratum and Alcyonium hibernicum are also found but these are much rarer and misidentification is unlikely.[3]

Biology

The colonies of dead man's fingers are nearly always either male or female, although a small number of hermaphrodite colonies are found. Colony growth occurs mainly in the first half of the year with the polyps becoming inactive in late summer, and the base tissue turning reddish or brownish due to the growth of algae and hydroids on the surface. At this time the gonads are developing and spawning occurs in December and January. Populations have been found to synchronize their gametogenesis and spawning activities.[5] Fertilisation takes place externally and the embryos float for a few days before developing into free swimming larvae. Most of these soon settle on a suitable substrate and new polyps develop but a few may remain in the zooplankton for some time and disperse over a wide area. Colonies have been known to live for twenty years.[5]

The polyps feed at various times of the day with their tentacles extended. They are suspension feeders gathering plankton from the water with the help of cilia, and absorbing oxygen at the same time.[1]

References

  1. ^ a b c Encyclopedia of Life
  2. ^ MarLIN
  3. ^ a b Encyclopedia of Marine Life of Britain and Ireland
  4. ^ World Register of Marine Species
  5. ^ a b [Hartnoll, R.G. (1975). The annual cycle of Alcyonium digitatum. Estuarine, Coastal and Shelf Science 3: 71-78.
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