Biology
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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).
Conservation
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Not relevant.
Description
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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).
Habitat
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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).
Range
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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).
Status
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англиски
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Not threatened (3).
Threats
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This species is not threatened.
Associations
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Animal / predator
adult of Simnia patula is predator of flesh of Alcyonium digitatum
Other: sole host/prey
Brief Summary
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англиски
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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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Alcyonium digitatum
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Alcyonium digitatum or dead man's fingers is a species of soft coral in the family Alcyoniidae. It is found around the coasts of the northern Atlantic Ocean and other temperate waters such as the South Pacific.
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, most recently being discovered in the unchartered waters of Jammerbugt bay off the north-west coast of Denmark by a 2020 seafloor mapping project led by explorer Klaus Thymann.[4] The species also occurs in parts of Canada, northeastern coast of the United States, the Gulf of Maine and the Bay of Fundy and the northern waters of New Zealand.[5] 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.[6] 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.[6]
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
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Alcyonium digitatum: Brief Summary
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Alcyonium digitatum or dead man's fingers is a species of soft coral in the family Alcyoniidae. It is found around the coasts of the northern Atlantic Ocean and other temperate waters such as the South Pacific.
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Diet
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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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Habitat
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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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