Overview

Comprehensive Description

General Description

A gelatinous, non-calcified bryozoan that is yellow or pale brown in colour. Colonies are stalked and stand erect from the substrate. The colony grows in finger-like lobed branches, and frequently exceeds 30 cm in height. When undisturbed, small white lophophores emerge from the surface. A. diaphanum is widely distributed and abundant in the coastal waters of the British Isles and the southern North Sea. Colonies are often dragged up in fishing nets, especially in the "weedy" areas of Dogger Bank, where this bryozoan is particularly abundant.

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Description

 Alcyonidium diaphanum forms an erect colony that can grow up to 50 cm long but more usually 15 cm. It has a small encrusting base, which attaches to hard substratum. The colour of Alcyonidium diaphanum can be light honey, brown, pale yellowish, grey, reddish, dark mahogany or even colourless. The size, colour and colony form varies widely around the British Isles.Other common names include "curly weed", "amber weed" and ju-ju weed" (Pathmanaban et al., 2005).  

Alcyonidium diaphanum is responsible for the allergic contact dermatitis, termed 'Dogger Bank Itch', experienced mostly by fishermen and dock workers (Pathmanaban et al., 2005). Although previously not reported from any other fishing grounds around the British Isles (Hayward, 1985), and despite its name, Dogger Bank Itch has also been reported from trawler-men in le Havre, shell fishermen from Cornwall and fixed net fishermen in the eastern English Channel (Pathmanaban et al., 2005).

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Description

This is a fleshy bryozoan, which is sometimes mistaken for a tunicate or sponge. It consists of thin finger-like growths, variously branched or webbed together. When undisturbed small white zooids with a crown of tentacles emerge from all surfaces. Some other species of Alcyonidium are similar and others are encrusting.
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Distribution

Distributed around the whole of the British Isles. Particularly abundant in the North Sea. Common along the English and French coasts of the English Channel and throughout the Irish Sea. Dense populations have been reported from the greater Thames Estuary, the coasts of the Netherlands and Belgium.

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Widespread all round the British Isles.
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Physical Description

Morphology

A. diaphanum colonies exhibit morphological plasticity. Six colony  morphotypes are recognised:

   

1. The knobbly column morphotype which has short tapered cylindrical lobes, up to 20 mm long, that are closely spaced and radially distributed along the entire length of the colony

2. The cylindrical morphotype is cylindrical along its entire length

   

3. The flat laminar morphotype is approximately cylindrical at the attachment point, but broadens into a flat section before tapering towards the distal tip.

   

4. The bushy morphotype

   

5. The sausage morphotype

   

6. The bootlace morphotype

   

The six morphotypes show geographic variation in their distribution, with the bushy and sausage forms thought to be limited to particular geographic areas.

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Diagnostic Description

Colony erect; cylindrical, laminar or irregularly branched, firm textured, up to 30 cm tall. Body wall of autozooids bounded by a thickened epicuticle, folded and papillate, with adjacent folds fusing to enclose exterior spaces, incorporating them within the colony structure. Autozooids with papillate orifices opening on all surfaces of the colony, the polypides orientated perpendicular to colony surface. Colony growth proceeds through intercalary frontal budding. Lophophore with 14 to 16 tentacles. Embryos lecithotrophic, brooded in multiples within the maternal autozooid. No intertentacular organ. (Porter et al, 2001).

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Look Alikes

May be confused with Alcyonidium hirsutum  A. hirsutum tends to be less gelatinous and will not directly attach to rock.

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Ecology

Habitat

Depth range based on 550 specimens in 1 taxon.
Water temperature and chemistry ranges based on 114 samples.

Environmental ranges
  Depth range (m): 0 - 420
  Temperature range (°C): -1.315 - 12.270
  Nitrate (umol/L): 1.402 - 12.502
  Salinity (PPS): 31.635 - 35.352
  Oxygen (ml/l): 6.017 - 7.743
  Phosphate (umol/l): 0.273 - 0.961
  Silicate (umol/l): 0.987 - 9.703

Graphical representation

Depth range (m): 0 - 420

Temperature range (°C): -1.315 - 12.270

Nitrate (umol/L): 1.402 - 12.502

Salinity (PPS): 31.635 - 35.352

Oxygen (ml/l): 6.017 - 7.743

Phosphate (umol/l): 0.273 - 0.961

Silicate (umol/l): 0.987 - 9.703
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Extends from extreme low water spring tides to about 100 m. Occurs only rarely in the intertidal on British coasts. Tolerant of estuarine conditions.

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 Alcyonidium diaphanum is found attached to rocks, shells or stones from the lower intertidal zone to shelly sands and coarse grounds offshore.
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Very common in the sublittoral zone in a wide range of habitats, attached to rocks or shells.
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Relevance to Humans and Ecosystems

Risks

Risk Statement

A. diaphanum  commonly causes an unpleasant allergic dermatitis. This condition is referred to as "Dogger Bank Itch" and produces large painful, weeping blisters. Sensitization, through frequent contact, results in increasingly painful recurrent attacks. Carle et al (1982) have isolated the allergen responsible and characterised the condition as a type 4 allergic reaction. Fishermen are prone to the dermatitis if they are not wearing the correct gloves.

 

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Wikipedia

Alcyonidium diaphanum

Alcyonidium diaphanum is a species of bryozoan found in the North Atlantic. It is known as "Sea-chervil", when it is found washed on the shore.

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