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.

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