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Home › Sea Life › Coral Ecosystems › Alcyonium Digitatum

Facts about Dead Man's Fingers

[Phylum: Cnidaria] [Class: Octocorallia] [Order: Alcyonacea] [Species: Alcyonium Digitatum]

There is a colonial species of soft coral with branching, fingerlike encrustations (lobes) that look like the fingers of an upturned human hand.

This section contains facts and information about the dead man's fingers coral species, and why this epifaunal sea creature with a gruesome sounding name thrives around the United Kingdom coastlines.

Dead Man's Fingers Distribution and Habitat

Besides being found in superabundance around all UK and Irish coasts, the northern Atlantic distribution of Alcyonium digitatum also includes:

• Denmark
• Iceland
• Norway
• Portugal

In addition, this particular species of soft coral is also found in certain temperate waters, especially the South Pacific.

By and large, dead man's fingers attach themselves to large underwater stones, gullies, and other types of rocky structures. But, it is not uncommon to find them living on the rigid external shells of some crab species or marine gastropods.

They prefer areas that have strong fast-flowing water movement, especially the sublittoral zones down to about 50 metres. Hence, a lack of strong sunlight results in a reduction of rapid algae growth.

Pro Tip: It's quite easy for the untrained eye to confuse dead man's finger coral with the less common species of blood-red coloured Alcyonium glomeratum (red sea fingers), Alcyonium hibernicum (pink sea fingers), or Codium fragile (green sea fingers).

Alcyonium Digitatum Characteristics

Because this colonial coral often lives on the surface of other organisms (Epibiotic), they display a range of external colourations.

But, for the most part, the fleshy stout encrustations of dead man's finger polyps are white, cream, yellow, orange, or reddish brown.

The colonies may appear to be 'furry' in appearance. However, several layers of hardened body parts (sclerites) actually form a leathery crust.

Here's the thing:

A large colony shares a gelatinous skeleton that branches into multiple fingerlike tentacles - or leathery lobes.

Yet, as these digitate invertebrate animals grow upwards from the base, they can reach a height of twenty (20) centimetres.

Pro Tip: Like many examples of small invertebrate marine animals, the dead man's fingers soft coral feeds on a combination of microscopic marine algae (phytoplankton) and tiny aquatic microorganisms that drift in the water column (zooplankton). In other words, they are typical suspension feeders that use extended tentacles (e.g. cilia) to devour their prey.

Dead Man's Fingers Reproduction

Most of the colony growth occurs in the first six months of the year. Even though the gender of almost all colonies will be either all male or all female, less than 1% will be hermaphroditic (able to produce both male and female gametes).

After a long period of inactivity during the summer months, gametogenesis and spawning usually takes place in the dark winter months (December and January in United Kingdom dive sites).

But wait - there's more:

A release of gametes into the water column is the signal for external fertilisation to occur. Then, neutrally buoyant embryos (lecithotrophic planulae) float for up to a week while they develop as free swimming larvae.

Many continue floating in the zooplankton for several days and disperse over a wide area. But, the ones that settle on a suitable substrate, such as bedrock, will start to develop new polyps.

Threats and Predators

Compared with some soft coral species, the lifespan of Alcyonium digitatum is quite significant and it can be more than twenty (20) years in some cases.

In fact, some colonies of dead man's fingers reached a height of fifteen (15) centimetres after ten years of growth.

Pro Tip: The IUCN Red List of Threatened Species, and Wildlife Trusts in the United Kingdom, currently list most species of dead man's fingers as being of "Least Concern" (LC).

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