Dead man’s fingers (Alcyonium digitatum)
|Size||Colony height: up to 200 mm (2)|
Not threatened (3).
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).
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).
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).
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).
This species is not threatened.
For more on this species see:
Budd, G.C. (2001) Alcyonium digitatum. Dead man’s fingers. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. [On-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 27/11/2003]. Available on-line at:
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- Cilia: microscopic hair-like appendages found on the surface of cells or single-celled organisms. In some species, cilia are used in locomotion or in feeding; by rhythmically contracting they can generate currents in the surrounding fluid.
- Hermaphroditic: possessing both male and female sex organs.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Plankton: aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
- Polyp: typically sedentary soft-bodied component of cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.
Budd, G.C. (2001) Alcyonium digitatum. Dead man’s fingers. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. [On-line]. Plymouth: Marine Biological Association of the United Kingdom. (November, 2003)
- Fish, J.D. and Fish, S. (1989) A student’s guide to the seashore. Unwin Hyman Ltd., London.
- Gibson, R., Hextall, B. and Rogers, A. (2001) Photographic Guide to the Sea & Shore Life of Britain and North-west Europe. Oxford University Press, Oxford.