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

Swiftia pallida would be removed by removal of the substratum, therefore intolerance has been assessed as high. Recovery would depend on the proximity of viable adults in the locality, as larval distribution is limited. If an entire population were removed, then recovery is unlikely. Hence recoverability is assessed as very low, resulting in a very high sensitivity assessment.

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

Swiftia pallida usually grows to heights of less than 10cm, so smothering is likely to kill small colonies, and probably cause mortality of the polyps which are buried in larger colonies. Hence intolerance is assessed as intermediate. Recovery is dependant on the presence of viable adults near by, so if the entire population consists of small colonies that will be killed, recovery is very unlikely. If, however, the population contains colonies which grow above the benchmark level of 5 cm, then recovery is likely, but will probably take several years. Therefore recovery is assessed as low, resulting in a high sensitivity ranking.

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

Swiftia pallida is thought to be tollerant of some siltation (Mitchell et al., 1983), and is found on rocks covered with a fine layer of silt. Further, while siltation may inhibit feeding, colonies of the sea fan Eunicella verrucosa produce mucus to clear themselves of silt (Hiscock pers comm.). Therefore Swiftia pallida has been assessed as tolerant to this factor, and is not sensitive.

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

It is possible that Swiftia pallida may feed on small particulate matter in suspended sediment, so a large reduction in this factor may result in reduced food availability for the sea fan. However at the benchmark level of a one month change, the effects are deemed unlikely to be fatal, so the species has been assessed as tolerant. Recovery is likely to be immediate on return to normal conditions, therefore not sensitive has been recorded.

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

Sea fans are found only in the circalittoral where desiccation will not occur.

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

Sea fans are found only in the circalittoral and so changes in emergence are not relevant.

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

Sea fans are found only in the circalittoral and so changes in emergence are not relevant.

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

Sea fans are found in strong tidal streams but most likely retract their polyps when current velocity gets too high for the polyps to retain food (Hiscock pers. comm.), leading to a reduction in viability. Tidal streams exert a steady pull on the colonies and are therefore likely to detach only very weakly attached colonies. Hence intolerance has been assessed as intermediate. Due to limited recruitment and slow growth rate, recoverability is assessed as moderate, therefore sensitivity is moderate.

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

Swiftia pallida is a filter feeder, so relies on high water flow rates to bring food and to remove silt. Colonies deprived of food may be adversely affected and, without significant water flow to remove silt, silt may kill tissue leaving areas bare of coenenchyme to be colonized by encrusting organisms. Due to limited recruitment and slow growth rate, recoverability is assessed as moderate, therefore sensitivity is moderate.

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

Mitchell et al., (1983) suggested that the Scottish and Irish populations of Swiftia pallida are at the southern limit of the species range (although this is contested by Hiscock et al., 2001), all sources agree that an increase in temperature is likely to lead to reduction or loss of this sea fan (Hiscock et al., 2001; Jones et al., 2002). At the benchmark level of an increase of 2°C for one year, reproductive success may be impaired, leading to a loss of new recruits, but existing colonies are likely to persist. This would suggest an intolerance of intermediate, however the species had been assessed as highly intolerant, because as colonies die off populations are likely to gradually decrease in density over time after a critically high temperature threshold is reached. Hiscock et al. (2001) predicted the loss of all populations occurring in the Inner Hebrides and mainland western Scotland with a 2°C increase in summer surface temperatures over a 20 year period.
Temperature may also affect the incidence of disease (see Introduction of microbial pathogens/parasites).
Recovery is dependant on larval recruitment, which is thought to be local (Hiscock et al., 2001), but as reproduction may be dependant on lower temperatures, warmer waters are likely to reduce reproductive viability, so new recruits are not likely. Hence recoverability has been assessed as low, resulting in a high sensitivity value. Populations are unlikely to shift to a more northern distribution because they are self sustaining, so geographical barriers are likely to prevent more northern colonization, as "illustrated by the absence of Swiftia pallida from the Shetland Islands (Hiscock et al., 2001).

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

As the species may be at the southern limit of its distribution in the UK, Swiftia pallida is likely to be tolerant of, or possibly even benefit from a decrease in temperature. Therefore the sea fan has been assessed as tolerant and not sensitive. However, range extensions are unlikely due to limited larval distribution and geographical barriers (Hiscock et al., 2001).

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

Swiftia pallida is normally found in turbid waters at depths of 20 m or more, therefore a reduction in light penetration from increased turbidity is unlikely to affect this species. As such, Swiftia pallida has been assessed as tolerant, and not sensitive to this factor.

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

Swiftia pallida probably feeds primarily on plankton rather than suspended organic matter, therefore decreases in turbidity may reduce the amount of food available for the sea fan. However, due to insufficient information on the effects of this on the species, no assessment has been made.

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

Swiftia pallida is normally found below 18 m where strong surge does not occur, therefore this factor is no relevant. The pink sea fan Eunicella verrucosa has been observed to be detached by severe storms, however this species grows at shallower depths than Swiftia pallida.

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

Swiftia pallida is normally found below 18 m where strong surge does not occur, therefore this factor is no relevant.

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

Anthozoans have no known ability to detect 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

Anthozoans have no known ability for visual perception.

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

Entanglement in fishing nets and angling line can cause abrasion that may damage the coenenchyme and expose the gorgonin skeleton, which can facilitate the settlement of fouling epibionts, as is the case in the Pink seafan Eunicella verrucosa (Anonynous, 2006). Colonisation by fouling epibiota will increase drag, and may include species that bore into the skeleton and weaken the colony (impacts observed on the structurally similar sea fan Paramuricea clavata described by Bavestrello et al., 1997). Therefore intolerance is assessed as intermediate.
Eno et al. (1996) suggested that Eunicella verrucosa was "remarkably resilient" to impact from lobster pots. They found that some seafan colonies returned to an upright position immediately after impact, while others were permanently bent, which would reduce feeing efficiency. However Tinsley (2006) observed flattened seafans which had continued growing, with new growth being aligned perpendicular to the current, so clearly even colonies of Eunicella verrucosa which are damaged can continue to survive.
Healthy Eunicella verrucosa are able to recover from minor damage and scratches to the coenenchyme (Tinsley, 2006), and the coenenchyme covering the axial skeleton will re-grow over scrapes on one side of the skeleton in about one week (Keith Hiscock, pers. comm.). However, where whole individuals are killed recovery is likely to be low due to slow growth and poor recruitment, therefore overall recoverability is assessed as moderate. Hence a moderate sensitivity assessment has been made.

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

Swiftia pallida colonies grow attached to hard substrata, often perpendicular to the current. Displacement is likely to impair feeding and cause abrasion and mortality, as colonies are unable to re-attach to the substrata following displacement. Therefore intolerance to this factor is assessed as high, and recovery very low, resulting in a very high sensitivity value.

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

Insufficient
information.

Heavy metal contamination

Evidence

Insufficient
information.

Hydrocarbon contamination

Evidence

Insufficient
information.

Radionuclide contamination

Evidence

Insufficient
information.

Changes in nutrient levels

Evidence

No information could be found on the effect of a change in nutrient levels on Swiftia pallida. Sea fans feed on planktonic organisms and, although abundance of those organisms might change as nutrient concentrations vary, the long term effects on food sources are not likely to be significant (Keith Hiscock per comm.). Any colonies growing at shallow depths may be smothered by ephemeral algae, as is the case with Eunicella verrucosa, however the majority of Swiftia pallida are found below the photic zone at 18 m depth, so are assessed as tolerant to this factor.

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

Swiftia pallida occurs in full salinity conditions, where hypersaline conditions are unlikely, therefore this factor is not relevant.

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

No evidence was found on the tolerance of Swiftia pallida to a change in salinity. However the species occurs in fully saline conditions, so is assessed as highly intolerant to a decrease in salinity. Recovery would be very low due to poor larval recruitment and slow growth, therefore Swiftia pallida has been assessed as highly sensitive to a decrease in salinity.

Changes in oxygenation

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

Evidence

No information was found on the effects of hypoxia on Swiftia pallida. However, the species lives in fully oxygenated conditions with high water flow levels, so it is expected that the seafan would be highly intolerant of decreased oxygen levels. Recovery will depend on recruitment, but is unlikely if surviving colonies are distant due to poor larval dispersal. Therefore recoverability has been assessed as very low, resulting in a very high sensitivity value.

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

No information was found on disease in Swiftia pallida, however another seafan Eunicella verrucosa, suffers from a disease which causes necrosis of the Coenchyme tissue, allowing fouling organisms to settle on the exposed gorgonin skeleton. Diseased colonies have high concentrations of bacteria, particularly Vibrio tasmaniensis, which appears to induce disease at higher temperatures, as colonies became infected at 20°C but remained healthy at 15°C (Hall-Spencer et al.).

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

No non-native species are known to be associated with or adversely affect Swiftia pallida.

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

Swiftia pallida is not known to be harvested.

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

Seafans are vulnerable to damage by mobile fishing gear, particularly in areas where they grow on low lying reefs adjacent to scallop beds (Tinsley, 2006). Trawling is likely to remove or severely damage Swiftia pallida.
Eno et al. (1996) suggested that Eunicella verrucosa was "remarkably resilient" to impact from lobster pots. They found that some seafan colonies returned to an upright position immediately after impact, while others were permanently bent, which would reduce feeing efficiency. However Tinsley (2006) observed flattened seafans which had continued growing, with new growth being aligned perpendicular to the current, so clearly even colonies of Eunicella verrucosa which are damaged in this manner can continue to survive.
Despite the likelihood that Swiftia pallida is resilient to static fishing, it has been assessed as highly intolerant due to the effect of dredges and trawls. Recovery of dislodged seafans is unlikely, and these colonies will probably die. Settlement of new colonies is dependant on recruitment, and larval supply, which is low, therefore recoverability is assessed as very low, resulting in a very high sensitivity value.