The Marine Life Information Network

Substratum loss

Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details

Evidence

Alcyonium digitatum is permanently attached to rocky substratum. Removal of the substratum would also remove this species within the area under consideration and mortality is judged to be high.
Recoverability, see additional information below.

Smothering

Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details.

Evidence

Alcyonium digitatum is permanently attached to the surface of rocky substrata. Thus it would be unable to avoid the deposition of a smothering layer of material up to a depth of 5 cm. Some colonies can attain a height of up to 20 cm so would still be able to expand tentacles and columns of the polyps to filter feed, and materials may be sloughed off with a large amount of mucous (see siltation). Smaller / younger colonies that initially form encrustation's between 5 and 10 mm thick are likely to be killed by smothering as respiration is likely to be hindered and an intolerance of intermediate is recorded.
Recoverability, see additional information below.

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Alcyonium digitatum has been shown to be tolerant of high levels of suspended sediment. Hill et al. (1997) demonstrated that Alcyonium digitatum sloughed off settled particles with a large amount of mucous (see adult biology, additional information). Siltation is normally only a problem in sheltered areas, and the slope of the rock is also important as little silt will settle on vertical surfaces and overhangs (Hiscock & Hoare, 1973) where Alcyonium digitatum is found.

Decrease in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Desiccation

1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

The population of Alcyonium digitatum is predominantly subtidal so the factor is judged not relevant. However, a few specimens of Alcyonium digitatum may be found on the lower shore, attached to rocks where the otherwise dominant algae are inhibited by a lack of light, such as under overhangs and in crevices. Although their location may offer some protection form sunlight and a drying wind, these specimens are likely to be highly intolerant of desiccation as Alcyonium digitatum has a large surface area to volume ratio and turgid body form.

Increase in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Alcyonium digitatum is predominantly a subtidal species so the factor is judged not relevant. A change in emergence regime will only effect a small proportion of specimens found on the lower shore where it favours locations under overhangs and in crevices where otherwise dominant algae are inhibited by a lack of light. Thus to some extent its position on the substrata may protect this species from the desiccating factors of air and direct sunlight. Alcyonium digitatum has a large surface area to volume ratio, and a turgid body form which would make it prone to mortality caused by desiccation following a change in emergence and a longer exposure to air and direct sunlight.

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Alcyonium digitatum is a suspension feeder relying on water currents to supply food. It therefore thrives in conditions of vigorous water flow e.g. around Orkney and St Abbs (Scotland), where it may experience tidal currents of 3 and 4 knots during spring tides (Kluijver, 1993).

Decrease in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

A decreased water flow rate may impact upon Alcyonium digitatum in that feeding efficiency could decrease as less material (phytoplankton & zooplankton) would be brought into contact with the colonies. Also a lower energy environment favours siltation and although Alcyonium digitatum has been found to tolerate a high level of suspended sediment, the energetic cost of producing enough mucous to slough off deposited material may reduce the species viability and an intermediate intolerance is recorded. Recoverability, see additional information below.

Increase in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

The geographic range of Alcyonium digitatum from Iceland in the North, to Portugal in the South illustrates that the species is tolerant of a range of temperatures and it is unlikely that this species will be adversely affected by a long term temperature change in British waters.

Decrease in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

The geographic range of Alcyonium digitatum from Iceland in the North, to Portugal in the South illustrates that the species is tolerant of a range of temperatures and it is unlikely that this species will be adversely affected by a long term temperature change in British waters. Alcyonium digitatum was also reported to be apparently unaffected by the severe winter of 1962-1963 (Crisp, 1964).

Increase in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Alcyonium digitatum filter feeds on both phytoplankton and zooplankton. Increased turbidity that reduces the amount of light available for primary production by phytoplankton for a period of one month may impact upon the food resource available to Alcyonium digitatum. The effect of a change in turbidity and hence food resources is likely to be greater between February and July (when the colony is active) rather than between August and December when the colony is inactive. An intolerance of low is recorded as the species would only be suffering from a short term sub-lethal effect. However, Alcyonium digitatum may benefit indirectly from increased turbidity as decreased light penetration may cause the decline of algal species making new substrata available for larval settlement. Recoverability, see additional information below.

Decrease in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Increase in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Alcyonium digitatum is tolerant of very strong wave action and is unlikely to be adversely affected by increased wave exposure.

Decrease in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

In the absence of moderate or strong tidal streams, a decrease in wave action is likely to have an adverse effect on Alcyonium digitatum as food supplies will be reduced and siltation may occur (see siltation and water flow). Recoverability, see additional information below.

Noise

1. Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods.
2. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details

Evidence

Alcyonium digitatum does not have the ability to perceive noise.

Visual presence

Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details

Evidence

Alcyonium digitatum does not have the ability to detect the visual presence of objects.

Abrasion & physical disturbance

Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details.

Evidence

Alcyonium digitatum is prone to damage and abrasion by fishing gears e.g. rock hopper otter trawls and Newhaven scallop dredges that are designed to penetrate the sea bed (Hartnoll, 1998). In addition, the anchoring of boats for purposes of recreational diving may cause cumulative damage in heavily visited sites. Magorrian & Service (1998) reported that trawling for queen scallops resulted in removal of emergent epifauna and damage to horse mussel beds in in Strangford Lough. They suggested that the emergent epifauna such as Alcyonium digitatum were more intolerant than the horse mussels themselves and reflected early signs of damage (Service & Magorrian, 1997; Magorrian & Service, 1998; Service 1998). Veale et al., 2000 reported that the abundance, biomass and production of epifaunal assemblages, including Alcyonium digitatum, decreased with increasing fishing effort. An intolerance rank of intermediate is recorded as it is likely that the proportion of the population on vertical slopes and under overhangs will be unaffected by mechanical abrasion. The population inhabiting horizontal surfaces at greater depths are at risk from abrasion. However, the fact that Alcyonium digitatum is more abundant on high fishing effort grounds suggests that this seemingly fragile species is more resistant to abrasive disturbance than might be assumed (Bradshaw et al., 2000), presumably owing to the ability for the replacement of senescent cells and regeneration of damaged tissue in addition to the early larval colonization of available substrata. Recoverability, see additional information below.

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Alcyonium digitatum is likely to be highly intolerant of displacement. The species is permanently attached to the substratum and once displaced does not have the ability to re-establish its attachment. Recoverability, see additional information below.

Synthetic compound contamination

Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:

• evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity;
• evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity;
• evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity.

The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details.

Evidence

Smith (1968) reported dead colonies of Alcyonium digitatum at a depth of 16 m in the locality of Sennen Cove (Pedu-men-du, Cornwall) resulting from the offshore spread and toxic effect of detergents (a mixture of a surfactant and an organic solvent) e.g. BP 1002 sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill. Possible sub-lethal effects of exposure to synthetic chemicals, may result in a change in morphology, growth rate or disruption of reproductive cycle. The vulnerability of this species to concentrations of pollutants may also depend on variations in other factors e.g. temperature and salinity conditions outside the normal range. However, no additional information concerning the direct biological effects of synthetic compound contamination on Alcyonium digitatum has been found to comment further.

Heavy metal contamination

Evidence

Possible sub-lethal effects of exposure to heavy metals, may result in a change in morphology, growth rate or disruption of reproductive cycle. The vulnerability of this species to concentrations of pollutants may also depend on variations in other factors e.g. temperature and salinity conditions outside the normal range. However, no information on the direct biological effects of heavy metal contamination on Alcyonium digitatum has been found to comment further.

Hydrocarbon contamination

Evidence

The vast proportion of the population of Alcyonium digitatum is permanently subtidal and because oil pollution is mainly a surface phenomenon its impact upon circalittoral turf communities is likely to be limited (Hartnoll, 1998). In addition Alcyonium digitatum is able to retract its colonies and slough off material from its surface so may be able to tolerate a light oiling. However, Smith (1968) reported dead colonies of Alcyonium digitatum at a depth of 16m in the locality of Sennen Cove (Pedu-men-du, Cornwall) resulting from the offshore spread and toxic effect of detergents sprayed along the shoreline to disperse oil from the Torrey Cannon tanker spill (see synthetic chemicals).

Radionuclide contamination

Evidence

There is insufficient information available to comment on the biological effects of radionuclide contamination on Alcyonium digitatum.

Changes in nutrient levels

Evidence

Alcyonium digitatum is a passive suspension feeder on phytoplankton and zooplankton. Nutrient enrichment of coastal waters (eutrophication) that enhances the population of phytoplankton may be beneficial to Alcyonium digitatum in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). However, the survival of Alcyonium digitatum may be influenced indirectly. High primary productivity in the water column combined with high summer temperature and the development of thermal stratification (which prevents mixing of the water column) can lead to hypoxia of the bottom waters and Alcyonium digitatum is likely to be highly intolerant of periods of hypoxia (see oxygenation).

Increase in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Alcyonium digitatum does inhabit situations such as the entrances to sea lochs where low salinity may occasionally occur. However, its distribution and the depth at which it occurs suggest that Alcyonium digitatum is unlikely to survive significant dilution.

Decrease in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Changes in oxygenation

Benchmark.  Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details.

Evidence

Alcyonium digitatum mainly inhabits environments in which the oxygen concentration usually exceeds 5 ml l^-1 and respiration is aerobic. Assimilation of oxygen occurs simply by diffusion through the epidermis of exposed tissues and transport to tissues is facilitated by hydroplasmic flow and ciliary activity (Hickson, 1901). It is likely that Alcyonium digitatum would be highly intolerant of a period of hypoxia so an intolerance assessment of high is recorded. Recoverability, see additional information below.

Introduction of microbial pathogens/parasites

Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details.

Evidence

Alcyonium digitatum acts as the host for the endoparasitic species Enalcyonium forbesiand Enalcyonium rubicundum (Stock, 1988). Parasitisation may reduce the viability of a colony but not to the extent of killing them but no further evidence was found to substantiate this suggestion.

Introduction of non-native species

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

Insufficient
information.

Extraction of this species

Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Alcyonium digitatum is not a commercially exploited species.

Extraction of other species

Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Alcyonium digitatum is a sedentary species that might be expected to suffer from the effects of dredging. However it has been found present in great abundance on some high-effort scallop dredging grounds around the Isle of Man, Irish Sea (Bradshaw et al., 2000) (see also adult abrasion and physical disturbance). Hill et al., (1997) demonstrated that Alcyonium digitatum is tolerant of high levels of suspended sediment (that may be generated by dredging) as it sloughs off settled particles with a large amount of mucous. This mechanism may help Alcyonium digitatum survive in heavily disturbed areas and this seemingly fragile species is evidently more resistant to disturbance than might be assumed. An intolerance rank of intermediate is recorded as it is likely that the proportion of the population on vertical slopes and under overhangs will be unaffected by mechanical abrasion caused by equipment used to catch other species, whereas the population inhabiting horizontal surfaces at greater depths is at risk from abrasion. Recoverability, see additional information below.