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

Removal of the substratum will result in removal of adults and germlings of Halidrys siliquosa. Therefore, an intolerance of high has been recorded. Recoverability has been assessed as high (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

Adult plants are large and held upright by their air bladders when immersed. Therefore, smothering by 5 cm of sediment is likely to only cover the base of the plant and have little effect. Intertidal rock pool populations may be more intolerant, depending on the depth of the pool. However, young (up to 1 year old) plants do not bear air bladders, and, together with germlings, are likely to be smothered by the sediment, preventing photosynthesis, and potentially kill young plants. Germlings can survive for up to 120 days in the dark (Moss & Sheader, 1973), so may not be affected by smothering for a month (see benchmark), although any resultant anoxic conditions would probably be detrimental. The presence of a layer sediment has been shown to cause stress and considerable mortality in algal propagules, and sediment scour in flowing water may also remove and kill zygotes or germlings (Vadas et al., 1992). Smothering by epiphytes (see general biology) may reduce photosynthesis and increase drag on the thallus increasing its susceptibility to storm damage. Epiphyte communities have been shown to reduce light reaching the plant and decrease the rates of oxygen exchange with the surrounding water. This is especially true in eutrophic conditions, the result being a reduction in photosynthesis and metabolic stress in macrophytes (Sand-Jensen et al., 1985, Phillipart, 1995b) which will presumably affect macroalgae similarly. Nevertheless, Halidrys siliquosa is able to shed its outer cell walls in order to reduce surface epiphytes (Moss, 1982). Overall, younger or smaller plants, together with germlings may be killed and recruitment reduced. Therefore, an intolerance of intermediate and a high recoverability has been recorded (see additional information).

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

Increased suspended sediment concentrations will increase turbidity (see below). Suspended sediment settling on algal fronds is likely to reduce photosynthesis, and additional scour by sediment in water flow may adversely affect germling and reduce settlement. Halidrys siliquosa occurs in sheltered and very sheltered conditions, in which siltation rates may be high. Therefore, Halidrys siliquosa may tolerate suspended sediment and is unlikely to be significantly affected by an increase in suspended sediment concentrations for one month (see benchmark). Hence an intolerance of low has been recorded. Increased suspended sediment may reduce recruitment if it coincided with reproductive season. Recovery is likely to be rapid (see additional information below).

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

A decrease in suspended sediment is unlikely to have any direct affects on Halidrys siliquosa, except to decrease turbidity (see below).

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

Halidrys siliquosa occurs subtidally, in the sublittoral fringe and is restricted to rockpools in the intertidal. Therefore, it is intolerant of desiccation. It is protected from exposure to desiccation in rockpools and subtidally, however, sublittoral fringe populations may be exposed to the air. Therefore, an increase in desiccation at the benchmark level is likely to adversely effect a proportion of the population and an intolerance of intermediate has been recorded. Recoverability has been assessed as high (see additional information below).

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

A one hour increase in emergence is likely to expose the upper portion of the population, especially in the sublittoral fringe, to desiccation, increased wave action and an increased range of temperature change. Halidrys siliquosa is restricted to rock pools in the intertidal, therefore increased emergence is likely to result in loss of the exposed plants, a loss of a proportion of the population. Hence, intolerance has been assessed as intermediate with recoverability of high (see additional information below).

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

Decreased emergence and hence, increased immersion may allow Halidrys siliquosa to colonize further up the shore. Therefore, the population may benefit overall.

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

Water flow is important to supply nutrients and oxygen, and water flow has been shown to increase photosynthesis in Halidrys siliquosa (Schwenke, 1971). Halidrys siliquosa was reported from the 'rapids approaches' in association with Himanthallia elongata and Saccharina latissima (studied as Laminaria saccharina), and may occur in association with Laminaria digitata in strongly flowing tidal streams (Lewis, 1964). Halidrys siliquosa decreases in abundance with increasing water flow, so that in tidal rapids with current speeds of 2-3m/sec (ca 6 knots), it is replaced by Laminaria digitata, Laminaria hyperborea and Saccorhiza polyschides communities (Lewis, 1964; Schwenke, 1971). An increase in water flow from, for example, weak to strong (see benchmark) it likely to significantly reduce the population within a year, resulting in its replacement by species tolerant of strong water flow. Therefore, an intolerance of high has been recorded with a recoverability of high (see additional information below).

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

Halidrys siliquosa occurs in moderately strong to weak tidal streams, as well as in rock pools, and is probably tolerant on stagnant water in the short term. Therefore a further decrease in water flow is unlikely to have an adverse effect. Reduced water flow may reduce oxygen and nutrient exchange, therefore an intolerance of low has been recorded. Recoverability will probably be immediate.

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

Lüning (1984, 1990) reported an upper survival temperature of 25 °C after one week exposure in Halidrys siliquosa. It did not survive at the higher temperatures studied. Zygote germination and growth are temperature dependant. Moss & Sheader (1973) reported 50-97% germination at 3 and 10 °C, falling considerably to 8 -52% at 20 °C and to zero at 22 °C. Growth increased with temperature up to 20 °C but germlings developed abnormally at 20 °C (Moss & Sheader, 1973).
Halidrys siliquosa is distributed from northern Norway to northern Portugal and also occurs in rock pools, which may experience a relatively large temperature range. Therefore, it is unlikely to be affected by long term temperature changes within the British Isles. Short term acute change may have adverse effects if the change increased the temperature over 20-25°C, especially if the change coincided with the release of gametes or the germination of zygotes. However, Halidrys siliquosa releases gametes and zygotes in the winter months (December to March). Overall, Halidrys siliquosa is probably tolerant to changes of temperature 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

Little information concerning the effects of low temperatures on Halidrys siliquosa was found. Lüning (1984, 1990) reported that it survived at 0 °C for one week, and Moss & Sheader (1973) reported that the lower limit of germination was not reached at 3 °C but that no gametes were released from fertile receptacles at -4 °C. Halidrys siliquosa is protected from ice scour or severe frosts by its subtidal or rock pool habit. Overall, Halidrys siliquosa is recorded from northern Norway and is probably tolerant to decreases of temperature likely to occur in British waters.

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

Increased turbidity decreases light penetration and hence decreases photosynthesis, plant growth and reproduction. Moss & Sheader (1973) demonstrated that the growth of germlings was dependent on light intensity but that germlings could survive total darkness for 120 days (see general biology). Halidrys siliquosa occurs in sheltered waters that may already be of medium to high turbidity (see benchmark), therefore an additional increase in turbidity may adversely effect the population. A short term increase may not have significant effects. An increase from medium to high turbidity for a year is likely to result in loss of the deepest extent of the population. Therefore, an intolerance of intermediate has been reported. Extreme turbidity for a year is likely to result in loss of macroalgae. Recoverability has been assessed as high (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

Decreased turbidity and hence increased light penetration is likely to benefit all macroalgae present, and may allow the Halidrys siliquosa population to extend to greater depths. Moss & Sheader (1973) noted that Halidrys siliquosa germlings approached photosynthetic saturation at light intensities about 5 fold those of early sporophytes of Laminaria hyperborea, possibly an adaptation to exposure to high light intensities in rock pools. Therefore, the population is likely to benefit from decreased turbidity

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

Halidrys siliquosa is most abundant on sheltered shores but is found on wave exposed shores where it occurs, primarily in deep mid-shore pools (Lewis, 1964). Halidrys siliquosa develops as a short, stunted turf in wave exposed pools (Moss & Lacey, 1963; Lewis, 1964) suggesting that it can tolerate strong water movement (Lewis, 1964). However, with increasing wave exposure Halidrys siliquosa / Saccharina latissima (studied as Laminaria saccharina) communities are replaced by Laminaria digitata or Laminaria hyperborea communities (Lewis, 1964). Therefore, intolerance of high has been recorded with a recoverability of high (see additional information).

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

Halidrys siliquosa is associated with wave sheltered rocky substrata (Lewis, 1964). A decrease in wave exposure is likely to allow Halidrys siliquosa to colonize space and to increase in extent. Therefore, the population may benefit from a decrease in wave exposure.

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

Macroalgae are not known to perceive noise of vibration.

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

Although macroalgae respond to light, they have no 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

Physical disturbance by a scallop dredge (see benchmark) may damage or remove some individuals. Therefore, an intolerance of intermediate has been recorded. Damaged individuals with intact holdfasts, i.e. not removed, will probably survive.

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

Halidrys siliquosa is permanently attached to the substratum and once removed would not be able to reattach. Therefore, displaced individuals would be lost and an intolerance of high has been recorded. Recoverability has been assessed as high (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

No information on the intolerance of Halidrys siliquosa to synthetic chemicals was found, however, information on other Fucales was available.
Fucoids are generally quite robust in terms of chemical pollution (Holt et al., 1995, 1997), e.g. Fucus sp. seems to thrive in TBT-polluted waters (Bryan & Gibbs, 1991). However, Rosemarin et al. (1994) stated that brown algae (Phaeophyta) were extraordinarily highly sensitive to chlorate, such as from pulp mill or brine electrolysis effluents (Holt et al., 1997). In the Baltic, Fucus vesiculosus disappeared in the vicinity of pulp mill discharge points and was adversely affected even at immediate and remote distances (Kautsky, 1992). Different life stages of Fucus serratus differ in their intolerance to synthetic chemicals. Scalan & Wilkinson (1987) found that spermatozoa and newly fertilized eggs of Fucus serratus were the most intolerant of biocides, while adult plants were only just significantly affected at 5ml/l of the biocides Dodigen v181-1, Dodigen v 2861-1 and ML-910. Herbicides (e.g. Diuron and Linuron) in agricultural or urban runoff are likely to be highly toxic to algae (Cole et al., 1999).
Therefore, given the reported intolerance of brown algae to chlorates, and their potential intolerance to biocides and herbicides, an intolerance of intermediate has been recorded albeit at very low confidence. Recoverability has been recorded as high (see additional information below).

Heavy metal contamination

Evidence

Holt et al., (1995, 1997) reported that fucoids and other algae were capable of retaining and concentrating heavy metals, so much so that Fucus spp. are used as indicators of heavy metal pollution. Alginates found in fucoids (and in Halidrys siliquosa) strip heavy metals and some radionuclides from seawater and store them in inert forms. Hence, adult plants are considered to be relatively tolerant of heavy metal contamination. however, younger stages may be more intolerant. for example iron ore dust interfered with the interaction between eggs and sperm in Fucus serratus (Boney, 1980; cited in Bryan, 1984). Bryan (1984) also reported that heavy metals retarded growth in brown algae, and suggested that heavy metal toxicities to seaweeds was in the order of Hg>Cu>Ag>Zn>Zn>Cd>Pb.
Overall, it appears that members of the fucales, and by inference Halidrys siliquosa are relatively tolerant of heavy metal pollution and an intolerance of low has been recorded.

Hydrocarbon contamination

Evidence

Halidrys siliquosa is protected from the direct effects of oil spills due to its subtidal habit, although sublittoral fringe and rock pool populations will be more vulnerable. However, plants may be exposed to water soluble components of the oil or oil adsorbed on to particulates.
No information concerning the effects of oil on Halidrys siliquosa was found. Holt et al. (1997) suggested that fucoids had limited intolerance to oil but noted that studies on long-term exposure were limited. For example, adult Fucus serratus plants are tolerant of exposure to spills of crude oil although very young germlings are intolerant of relatively low concentrations of 'water soluble' extractions of crude oils. Exposure of eggs to these extracts (at 1.5 micrograms/ml for 96 hours) interferes with adhesion during settling and at 0.1micrograms/ml) prevented further development (Johnston, 1977). Fucus vesiculosus showed limited intolerance to oil. After the Amoco Cadiz oil spill Fucus vesiculosus suffered very little (Floc'h & Diouris, 1980). Indeed, Fucus vesiculosus, may increase significantly in abundance on a shore where grazing gastropods have been killed by oil. However, very heavy fouling could reduce light available for photosynthesis and in Norway a heavy oil spill reduced fucoid cover.
Therefore, it appears that fucoids, and by inference Halidrys siliquosa, have a limited intolerance to hydrocarbons and an intolerance of low has been recorded.

Radionuclide contamination

Evidence

Ryan et al (2003) report on radioactivity levels in various fucoids around Ireland although no specific information was found on either Halidrys siliquosa or effects on fucoids in general.

Changes in nutrient levels

Evidence

Wernberg et al. (2001) reported that the N:P (nitrogen to phosphorus) ratio in Limfjorden Halidrys siliquosa was low in summer and high in spring, which suggested that growth was nutrient limited by P in spring and N in summer. Kindig & Littler (1980) exposed Halidrys dioica and other algae to 10% untreated sewage effluent in the field, which resulted in increased gross productivity. However, Halidrys dioica was found to be absent in the vicinity of a sewage outfall, and Kindig & Littler (1980) concluded that another component of the effluent, other than nutrient, was responsible. Overall, therefore, it would appear that moderate nutrient enrichment at the benchmark level may stimulate growth of Halidrys spp. However, excessive enrichment may lead to eutrophication, decreased oxygen levels (see below) and the potential smothering of Halidrys sp. by microfloral epiphytes (see smothering).

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

No information on salinity tolerance was found. However, Halidrys siliquosa occurs in rock pools, which may experience considerable fluctuations in salinity due to evaporation on hot days. Therefore, Halidrys siliquosa is probably tolerant of fluctuations in salinity, both increases and decreases, and an intolerance of low has been recorded.

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 information on salinity tolerance was found. However, Halidrys siliquosa occurs in rock pools, which may experience considerable decline in salinity due to freshwater influence during rain. Therefore, Halidrys siliquosa is probably tolerant of fluctuations in salinity, both increases and decreases, and an intolerance of low has been recorded.

Changes in oxygenation

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

Evidence

Little information on the effects of oxygen depletion on macroalgae was found. Kinne (1972) reports that reduced oxygen concentrations inhibit both photosynthesis and respiration. The effects of decreased oxygen concentration equivalent to the benchmark would be greatest during dark when the macroalgae are dependant on respiration.

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

Halidrys siliquosa supports a number of epiphytic species, which use it as a substratum but are not parasitic on the plant. No information on diseases was found.

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

Halidrys siliquosa has been reported to be displaced as the dominant species in rock pools by the non-native Sargassum muticum on the south coast of England (Eno et al., 1997). Staehr et al. (2000) reported that an increase in the abundance of Sargassum muticum in Limfjorden, Denmark had resulted in a significant decline of the cover of large brown algae, especially Saccharina latissima (studied as Laminaria saccharina), Halidrys siliquosa, Codium fragile and Fucus vesiculosus.
Therefore, Sargassum muticum appears to able to completely replace or significantly reduce the extent of Halidrys siliquosa, and other algae, and an intolerance of high has been recorded. Recoverability has been assessed as high (see additional information below).

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

No evidence of the extraction or harvesting of Halidrys siliquosa was found.

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

Svendsen (1972; summary only) reported that Halidrys siliquosa became one of the dominant macroalgae, 3 years after kelp harvesting in Norway. This suggests that removal of other algae species that compete with Halidrys siliquosa for space and light would be beneficial.